Consider a body moving along a straight line accelerating uniformly from velocity u to final velocity v within time t.
If we represent the distance covered between the initial and final velocity to be s; then there are three equations that can represent such a movement:
1. v=u + at
2. s=ut + (1/2)at2
3. v2 = u2+2as
Deriving First equation
Multiplying by t on both sides:
at = v-u
Making v the subject by adding u on both sides:
at + u = v-u + u
Hence
v=u + at ————-(ii)
Deriving second equation of linear motion
From linear motions;
we can as well obtain velocities at different points in the motion and then divide by the number of points to get the average velocity.
Similarly given the initial velocity u and final velocity v, we can obtain average velocity as :
But
distance s= average velocity x time t , that is;
From the first equation;
v=u + at
Hence
and opening the bracket we get;
and therefore second equation is usually stated as:
Deriving third equation of linear motion
From the equation; v=u + at
but also, average velocity is total displacement s divided by total time t. that is;
cross multiplying the equation above we obtains:
2s=(v+u)t
and substituting t for v-u/a, we have;
2s=(v+u)(v-u)/2
and expanding the brackets we have
and so we have;
but -uv + uv = 0 and so we get
2as=v2-u2
and then rearranging the equation to get:
v2=u2+2as ———(iii)
Sample problems involving linear motion
A car accelerates from rest at a rate of 3 ms-1. How long will it take for the car to reach a speed of 30m/s?
A train decelerates at a rate of 2m/s2 until it comes to a complete stop. If the initial speed of the train is 25m/s, how far will it travel before stopping?
An object is thrown vertically upward with an initial velocity of 20 m/s. How long will it take for the object to reach its maximum height?
A ball is dropped from a height of 50 m. What is its velocity after 3s?
A cyclist travels at a constant speed of 10m/s for 20 s. How far does the cyclist travel during this time?
A stone is thrown horizontally from the top of a cliff with a velocity of 15m/s. How far does the stone travel horizontally before hitting the ground if it takes 3s to reach the ground?
An airplane accelerates down a runway at a rate of 2m/s2 until it reaches a takeoff speed of 60m/s. If the runway is 1500 m long, how long does it take for the airplane to take off?
A rocket is launched vertically upward with an initial velocity of 50m/s. How high does the rocket go before it starts to fall back down?
Electromagnetic waves have a vast range of practical everyday applications such us telecommunication, Wi-Fi, cooking, vision, medical imaging, treatment of diseases etc. Each type of wave has it’s unique application that largely depends on it’s energy.
Gamma Radiations
Used in medicine to sterilize medical equipment. They are also focused towards cancerous cells and other malignant growth in the body.
In industries, gamma rays are used to detect flaws in metals courtesy of their high penetrating power. They can detect cracks according to variation in thickness and can also detect density change, weld defect, and non-uniformity of material. Also used to check oil pipelines to detect weak points.
In hospitality industries they can helps to preserve food for a longer period.
can be used to generate nuclear reactions.
They are used to study the structure of the nucleus of the atom.
X-rays
Applied in medicine for radiology done to identify nature of internal body structures like bones. They are therefore used to locate bone fractures or foreign objects like small metals that could have accidentally entered into animal or human body.
Other uses of x-rays includes:
Cancer therapy since the energy in the radiations are capable of killing malignant tissues.
used in Fluoroscopy where fluorescent screen is used to obtain real-time images of movement within the body or to view diagnostic processes, such as following the path of an injected or swallowed contrast agent.
irradiate pests and micro-organisms killing them.
used to study crystal lattice and detection of flaws in metals
Ultraviolet waves
Applications of Ultraviolet rays across various sectors of life includes
(i) Disinfection
UV radiation is used to kill bacteria, viruses, and other microorganisms where It is usually applied in water treatment plants, air purification systems and medical equipment sterilization. UV radiation is used to disinfect water by damaging the DNA of micro-organisms such as bacteria and viruses interfering with their ability to replicate. In a UV water disinfection system, water is passed through a chamber containing UV lamps. The UV light penetrates the cells of the micro-organisms, disrupting their genetic material and preventing them from reproducing therefore effectively killing harmful pathogens and making the water safe for consumption.
an overview of Ultraviolet water disinfection system
(ii)UV Curing in Printing
This is a process used in printing and coating applications to instantly dry and harden inks, adhesives and coatings using ultraviolet light. In UV curing systems, UV lamps emit high-intensity UV light onto the printed surface or coating material. where UV light initiates a photochemical reaction that polymerizes or cross-links the molecules in the ink or coating transforming it from a liquid to a solid state almost instantly which allows fast production speeds, reduced solvent emissions, and enhanced durability of printed materials.
UV curing system
(iii) Phototherapy for Skin Disorders
Used in phototherapy treatments for various skin disorders such as psoriasis and eczema. During phototherapy sessions, patients are exposed to controlled doses of UV radiation, typically UVBor narrowband UVB light, either from specialized UV lamps or natural sunlight.
The UV light penetrates the skin and slows down the overgrowth of skin cells, reduces inflammation, and promotes healing. Phototherapy can be administered in medical facilities or at home using specialized phototherapy devices under medical supervision.
A phototherapy device
(iv) UV Forensic Analysis
UV light is used in forensic investigations to detect and analyze various types of evidence such as bodily fluids, fibers and counterfeit documents. UV light can reveal hidden bloodstains on surfaces by causing them to fluoresce under UV illumination. It can detect security features and fluorescent markings on currency and official documents that are not visible under normal light.
Forensic investigators use specialized UV light sources, such as UV lamps or forensic light sources to illuminate the evidence and capture images for analysis and documentation hence used to detect forgeries.
Forensic-Light-Source-Kit at work
(v) UV-Aging Test for Materials
UV radiation is used in accelerated aging tests to simulate the effects of long-term exposure to sunlight on materials and products. In a UV-aging test, samples of the material or product are exposed to controlled levels of UV radiation in a specialized chamber equipped with UV lamps that emit UV-A and UV-B light. The exposure to UV radiation causes chemical and physical changes in the material, such as discoloration, degradation, and loss of mechanical properties, which can be analyzed to assess the material’s durability and performance under outdoor conditions.
Other uses includes:
Fluorescence Microscopy where UV light is used to excite fluorescent molecules within biological samples enabling the visualization of structures that wouldn’t be visible under normal light.
Vitamin D Production where UVB radiation triggers the synthesis of vitamin D in the skin, essential for bone health and other physiological process.
used as an Insect Traps where certain insects are attracted to UV light hence UV insect traps use this principle to lure insects towards the light source, where they are either trapped or killed.
Used in spectroscopy and mineral analysis.
In food industry, they are used to detect freshness of eggs
Visible light
Photography
Photography is about capturing images. In a digital camera, visible light enters through the lens and falls onto a photosensitive sensor (CCD or CMOS), where it is converted into electrical signals representing the colors and intensity of the scene.
CMOS Sensor Vs CCD Sensor
In traditional film photography, visible light exposes a light-sensitive film, producing a latent image that is later developed into a visible photograph.
Optical Communication
Visible light is utilized in optical communication systems for transmitting data over short distances. In fiber-optic communication, visible light usually from lasers or light-emitting diodes is transmitted through optical fibers made of glass or plastic. The light signals carry data encoded as variations in intensity or modulation. At the receiving end, photodetectors convert the light signals back into electrical signals for processing.
Spectroscopy
This is a technique used to analyze the composition and properties of materials based on their interaction with light. In a spectrophotometer, beam of visible light passes through a sample, and the intensity of the transmitted or reflected light is measured as a function of wavelength. By analyzing the absorption, emission or scattering of light by the sample, scientists can identify substances, quantify their concentrations, and study their molecular structure.
an optical-spectrometer
Vision and Imaging Technologies
Visible light is essential for animal and human vision and various imaging technologies. In the human eye, visible light enters through the cornea and lens, where it is focused onto the retina. Photoreceptor cells in the retina, called rods and cones, convert light into electrical signals, which are transmitted to the brain for image processing.
In imaging technologies such as digital cameras, visible light is used to capture images and record visual information.
Calorimetry and Color Analysis
Visible light is used in calorimetry and color analysis to quantify and characterize the color properties of objects. Colorimeters and spectrophotometers measure the spectral reflectance or transmittance of materials across different wavelengths of visible light. By analyzing the color spectra, scientists and engineers can determine parameters such as color coordinates, chromaticity, color temperature, and color rendering index (CRI), which are important for various applications, including color matching, quality control, and product design.
Electric Power Generation
Solar Photovoltaic (PV) Systems systems utilize visible light to generate electric power through the photovoltaic effect. Solar panels, composed of semiconductor materials like silicon, absorb sunlight and convert it directly into electricity. When photons from sunlight strike the surface of the solar cells, they transfer their energy to electrons within the semiconductor material, causing them to become excited and create an electric current. This current is then collected and converted into usable electrical power. Solar PV systems are widely used to generate clean and renewable energy, reducing reliance on fossil fuels and mitigating greenhouse gas emissions.
Plant Growth
Visible light is essential for photosynthesis, the process by which green plants, algae, and some bacteria convert light energy into chemical energy to fuel their growth and metabolism. During photosynthesis, chlorophyll pigments in plant cells absorb photons of light, primarily in the blue and red wavelengths, and use this energy to convert carbon dioxide and water into glucose and oxygen. The glucose serves as a source of energy for the plant, while the oxygen is released into the atmosphere as a byproduct. Adequate exposure to visible light is crucial for healthy plant growth, as it provides the energy necessary for photosynthesis to occur.
Artificial Lighting in Agriculture
In indoor farming, greenhouses, and controlled environment agriculture (CEA), visible light is supplied to plants using artificial lighting sources such as light-emitting diodes (LEDs). LED grow lights are designed to emit specific wavelengths of light that promote photosynthesis and optimize plant growth. By adjusting the intensity, spectrum and duration of light exposure, growers can tailor the lighting conditions to meet the needs of different plant species and growth stages. LED grow lights have revolutionized indoor farming by enabling year-round cultivation of crops in environments where natural sunlight may be limited or insufficient.
Green house farming
Infrared Radiations
Thermal Imaging
Infrared cameras detect the heat emitted by objects and convert it into an image visible to the human eye. This technology finds extensive use in various fields such as military and defense where thermal imaging is used for night vision, surveillance, and target detection.
It is also used in Building Inspections where Infrared cameras can identify heat leaks, moisture intrusion and electrical faults in buildings, facilitating energy efficiency and safety.
In medicine it is used in Medical Imaging where Infrared thermography is used in medicine for diagnosing conditions like inflammation, vascular disorders and breast cancer.
Remote Sensing
Infrared sensors are deployed in satellites and aircraft for remote sensing applications. By analyzing the infrared radiation emitted or reflected by Earth’s surface, scientists can gather information about vegetation, land use, ocean temperatures, and atmospheric conditions. This data is crucial for environmental monitoring, weather forecasting, and climate studies.
Communication and sensing
In communication industry devices like remote Controls uses Infrared radiations to controls televisions screen, home entertainment systems like woofer and other consumer electronics, allowing users to wirelessly operate devices within line-of-sight range.
Infrared proximity sensors detect the presence or absence of objects, enabling applications such as automatic faucets, motion-activated lighting, and smartphone proximity detection.
Infrared sensors can detect hand movements and gestures, enabling touchless interfaces in devices like smartphones, gaming consoles, and interactive displays.
Industrial Processes
Infrared radiation plays a significant role in industrial processes such as heating, drying, and curing.
Infrared heaters are used in applications like plastics processing, paint drying, food processing, and printing. They offer precise and efficient heating, reduce processing times, and can be tailored to specific materials and processes.
Infrared spectroscopy techniques are used for material analysis, chemical identification and quality control in industries such as pharmaceuticals, food and beverage, and materials science.
Security Systems
Infrared sensors are integrated into security systems for intrusion detection, motion sensing and perimeter monitoring. These sensors can detect human body heat and movement even in darkness making them suitable for surveillance purposes in both indoor and outdoor environments.
Environmental Monitoring
Infrared spectroscopy is employed in environmental monitoring to analyze gases in the atmosphere. By measuring the absorption or emission of infrared radiation by different molecules, scientists can identify and quantify pollutants, greenhouse gases and atmospheric constituents, aiding in air quality assessment and climate research.
Medical Applications
Infrared radiation is utilized in various medical treatments and diagnostics like:
Therapeutic Heating where Infrared lamps and heating pads are used for pain relief, muscle relaxation and promoting healing in conditions like arthritis and sports injuries.
Blood Glucose Monitoring where Some glucose meters utilize infrared technology to measure blood glucose levels without the need for pricking the skin.
Surgery where Infrared lasers are used in surgical procedures for cutting, coagulation, and tissue ablation with precision and minimal damage to surrounding tissues.
Industrial Heating and Processing:
Infrared heaters are employed in industrial processes such as plastics molding, food processing, paint curing, and drying applications, providing efficient and precise heating with minimal energy waste.
Infrared spectroscopy techniques are used for material analysis, chemical identification, and quality control in industries such as pharmaceuticals, food and beverage, and materials science.
used to warm green houses in agriculture.
Radio waves
Radio waves serve as the foundation for wireless communication systems, enabling the transmission of data, voice, and video signals over long distances. This includes:
Radio Broadcasting where amplitude modulation(AM) and FM frequency modulation(FM) radio stations use radio waves to broadcast news, music, and entertainment to listeners.
Television Broadcasting where terrestrial and satellite television broadcasters relies on radio waves to deliver audio and video signals to TV sets.
Cellular Networks where mobile phones and smartphones utilize radio waves to communicate with cellular towers, allowing users to make calls, send texts, and access the internet wirelessly.
Wi-Fi where Wireless internet connectivity in homes, businesses, and public spaces uses radio waves for local area networking (LAN) and internet access.
Radar Systems
Radar (Radio Detection and Ranging) systems use radio waves to detect the presence, location, and movement of objects. Radar finds applications in various domains, including:
Air Traffic Control where radar systems monitor and manage air traffic by tracking the positions and velocities of aircraft in real-time.
Weather Forecasting where weather radars detect precipitation, storms, and atmospheric conditions, aiding in weather forecasting, severe weather warnings, and climate research.
Military and Defense where radar is utilized for surveillance, target tracking, navigation, and missile guidance in military applications.
Navigation and Positioning
Global Navigation Satellite Systems (GNSS), such as Global Positioning System(GPS), Galileo and GLONASS, rely on radio waves transmitted by satellites to provide accurate location, velocity, and timing information for navigation purposes. GPS receivers use signals from multiple satellites to determine their position on Earth’s surface.
Medical Imaging
In the field of medicine, radio waves are utilized in Magnetic Resonance Imaging (MRI) machines to produce detailed images of internal body structures. MRI works by using radio waves to manipulate the magnetic alignment of hydrogen atoms in the body, generating cross-sectional images that aid in the diagnosis of various medical conditions.
Radio Astronomy
Radio telescopes detect and study radio waves emitted by celestial objects in the universe, providing insights into the structure, composition, and dynamics of galaxies, stars, planets and other astronomical phenomena. Radio astronomy contributes to our understanding of the cosmos and the origins of the universe.
Microwaves
Cooking
One of the most common household uses of microwaves is in microwave ovens for cooking and heating food. Microwaves penetrate food and cause water molecules to vibrate, generating heat throughout the food quickly and efficiently. This results in rapid cooking or reheating of meals, making microwave ovens a convenient kitchen appliance.
Communication
Microwaves are extensively used in telecommunications for transmitting voice, data, and video signals over long distances. This includes:
Satellite Communication where microwaves are utilized in satellite communication systems to transmit signals between ground stations and satellites orbiting the Earth. This enables global communication including television broadcasts, internet connectivity, and telephone calls.
Microwave Links where point-to-point microwave links are employed for high-speed data transmission between fixed locations, such as between buildings, cell towers, or across long distances in rural areas where laying fiber-optic cables may be impractical.
Radar Systems
Radar (Radio Detection and Ranging) systems use microwaves to detect the presence, location, and movement of objects. Microwaves are particularly well-suited for radar applications due to their ability to travel long distances and penetrate through various weather conditions. Radar finds applications in:
Air Traffic Control where radar systems monitor and manage air traffic by tracking the positions and velocities of aircraft in real-time.
Weather Forecasting where weather radars use microwaves to detect precipitation, storms, and atmospheric conditions, aiding in weather forecasting, severe weather warnings, and meteorological research.
Military and Defense where radar is utilized for surveillance, target tracking, navigation and missile guidance in military applications.
Medical Diagnostics and Therapy
Microwaves are employed in various medical applications such as:
Microwave imaging techniques, such as microwave breast imaging, where we use low-power microwaves to create detailed images of internal body structures for diagnostic purposes.
In cancer treatment, microwave ablation is used to destroy cancerous tumors by heating them with focused microwaves, causing cellular damage and necrosis.
Industrial Processes
Microwaves find applications in industrial heating and processing, such as:
Drying and Curing where microwaves are used for drying and curing materials in industries such as textiles, ceramics, and food processing, where rapid and uniform heating is required.
Material Processing where microwaves are employed in material processing tasks such as welding, sintering, and joining in manufacturing processes.
A transformer is a transfers electrical energy from one circuit to another by mutual induction. It consists of primary and secondary coil where an alternating current is fed into the secondary coil so that some current can be produced in the secondary coil due to magnetic field associated with flowing current.
A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit by having a varying current in any it’s coils which produces a varying magnetic flux in the transformer’s core inducing induces varying electromotive force (EMF) across any other coils wound around the same core.
Coils of a transformer are wound on a common soft iron core as shown.
Transformers are used to change AC voltage levels, increasing or decreasing it. They can also be used to provide galvanic isolation between circuits as well as to couple stages of signal-processing circuits.
The voltage in primary and secondary coils depends on the number of turns of wire on the coil.
Consider the set up below where initially the number of turns in secondary is equal to the number of turns in primary coil.
If the number of turns in the secondary coil is increased, the voltage in the secondary circuit is observed to increase and also the brightness of the bulb increases.
When an alternating current flows in the primary coil, it produces an alternating magnetic flux which links with turns of the secondary coil which then induces electromotive force (e.m.f) in the secondary coil.
The magnitude of the induced e.m.f increases with the number of turns of the secondary coil because an e.m.f is induced in each turn.
depending on the number of turns in secondary coil against the primary coil, we can have step-up or step down transformers
step-up transformers
This is a kind of transformer that multiplies voltage fed in primary coil so as to produce much more voltage in secondary coil. It has more turns on the secondary coil than those in primary coil such that the turn ration is greater than one.
since the turn ratio is greater than one, the primary voltage is multiplied by a factor that is greater than one.
The figure below illustrates a step up transformer
illustrating step-up transformer
The step up transformer is usually represented by the following symbol in diagrams.
symbol for step up transformer
step down transformer
It is a transformer that reduces power generating in primary coil. It has more turns in primary coil (Np) than in the secondary coil (Ns) such that the turn ratio is less than one. i.e.
The step down transformer multiplies the voltage in secondary by a factor less than one hence reducing it. It is useful when power supply company need to scale down the voltage transmitted so that it can be used by domestic consumers. The transformer near your homestead is most likely a step down transformer.
In the figure below, a step down transformer is illustrated showing less number of turns in secondary compared to primary coil
The figure below shows transformer symbols we use in books.
The degree to which a lens deviate light is called the optical power.
Optical power measures how sharp the lens bends light that passes through it . Optical power P is given by P=1/f where f is the focal length of the lens. From the equation, one can see that the shorter the focal length, the higher the optical power. The unit for optical power is m-1 .
m-1 is known as dioptre (D)
Len’s Combination
If an object is placed infront of a combination of two or more lenses, it’s image in the first lens becomes the object for the second lens which in turn produces another image. If there is a third lens, the second image becomes it’s object.
One application of the Len’s combination is the compound microscope which combines two converging lenses of short focal length. In the microscope, the lens near the object is known as the objective lens and one near the eye is referred to as the eyepiece. Eyepiece has longer focal length compared to objective lens.
Compound microscope structure
The object to be viewed is placed between Fo and 2Fo of the objective lens so that a real inverted and magnified image is formed. This image is infront of the eyepiece and will act as an object to it. The eyepiece is adjusted so that this image falls between it’s principal focus Fo and itself so that a virtual but magnified image is obtained. The eyepiece therefore acts as a magnifying glass and produces a final image that is greatly magnified as in the figure above
Compound Microscope magnification
Magnification of objective lens mo = u/v where v is the distance of the first image from the objective lens and u the object distance. Taking fo as the focal length of the object lens, then from the lens formula:
1/v + 1/u = 1/fo
multiplying through by v;
1 + v/u = v/fo
substituting mo = u/v; we have
1 + mo = v/fo and so mo = v/fo -1
similarly, magnification me produced by the eyepiece will be given as:
me = D/fe -1
where D is the distance of first image from the lens.
Total magnification produced by this lens arrangement is the product of mo and me
That is, Total magnification = ( D/fe -1)(v/fo -1 )
Oxford English dictionary describes force as strength or energy as an attribute of physical action or movement.
A force acts acts in a particular direction and have the following effects:
Effects of force
(i) change the state of motion of a body.
A body that is not moving can be set in motion when a force is applied on it and a moving body will stop when force is applied against it the opposite direction to it’s motion.
a moving body can increase its speed if a force is a applied on it in the direction of it’s motion and it’s motion can be reduced when an opposing force is acting against it’s motion. For example friction force reduces motion of an object dragged on a flat surface.
(ii) Distorts or changes shape of an object.
For example a force applied on a glass causes it to crack. When force is applied on an elastic material, it expands. A plastic bottle will change shape when force is applied on it. Similarly, a car that meet with an accident will have a bad shape.
distorted car after an accident
(iii) causes object to turn or changes direction.
when a force is applied on one end of the object when it is fixed from another point, the body tends to change direction. The change of direction from a fixed point is usually referred to as the turning effect of force. The figure below illustrates a spanner that turns about a fixed point in order to tighten or loose a nut.
spanner at work
Describing force
Force is also described as the source of energy which changes body’s state of motion, direction or shape. Large forces causes large effects on bodies and small forces has less significant effects on bodies.
Force always acts towards specific direction and so it is a vector quantity as it has both magnitude and direction
Force in diagrams is represented by a line with an arrow showing the direction in which it acts.
Electromagnetic waves are usually detected by devices or gadgets. The human eye can only detect only a small portion of this spectrum called visible light. A radio detects a different portion of the spectrum, and an x-ray machine uses yet another portion.
Gamma Rays
Detected by photographic plates and radiation detectors like Geiger Muller Tubes.
we need a gamma spectrometer to know the energy ranges of the γ photons emitted by a radioactive source. A gamma spectrometer generally consists of a scintillation detector or a semiconductor detector to convert the γ rays into visible light or electronic signals respectively. With a multi-channel analyser, a gamma spectrum depicting the number distribution of γ photons at different energy ranges can be obtained. The γ spectrum is like the “fingerprints” of nuclides which facilitate the identification of different nuclides in a radioactive source.
By counting the rate of charge pulses or voltage pulses or measuring the scintillation of the light emitted, the number and energy of gamma ray photon striking an ionisation detector or scintillation counter can be found.
Gamma spectrometer circuit
X-rays Detection
In X-ray detectors the energy transported by the radiation is converted into forms that can be recognized visually or electronically. Generally the photons are absorbed by the detector material and energy transfer takes place by ionization.
X-rays are usually detected by using a fluorescent screen or photographic film.
In hospitals, X-rays used to observe broken bones are detected by their actions on specially designed photographic emulsions. This high energy radiation may also be detected by its ability to ionise gas atoms producing a pulse of electric current in a gas placed between two electrodes.
Geiger Muller counter using the ionisation of gas atoms detects the presence of both X-rays and gamma rays.
X-ray detector
Detection of Ultraviolet Radiation
It is usually detected by photographic films, photocells, fluorescent materials like quinine and sulphate and a paper slightly smeared with vaseline.
Quinine, a substance found in tonic water is sensitive to UV light and can absorb UV light that we can’t see and then re-emit visible blue light that we can see in a process known as fluorescence
A fluorescent material is one that absorbs the energy of UltraViolet light and then re-emits it as visible light.
The inner surface of a fluorescent tube is coated with a fluorescent material .The tube is filled with a gas that emits UV light when made to conduct by a high voltage.
fluorescent lamps
Visible light
Common detectors of visible light are the eye, photographic film, charge-coupled devices (CCDs) and the photocell.
Photographic films detects light by the chemical changes it produces in light-sensitive chemicals such as silver halides. Light is also detected by the photoelectric effect in which its energy causes electrons to be emitted from metal surfaces.
By use of photoelectric effect, electrons are collected in a photomultiplier tube and the current they produce amplified to produce an electric signal.
Semiconductors are used to produce photovoltaic cells which generate a current when light falls on them and photoresistors in which incident light causes a change in electrical resistance.
visible light detectors
Detecting Infrared Radiation
It is usually detected by the heating effect produced on the skin, a thermopile, bolometer and thermometer with a blackened bulb.
A bolometer contains a blackened metal strip whose temperature rises when infrared radiations falls on it and this temperature is detected by measuring the change in electrical resistance of the strip.
When infrared radiation falls on semiconductor surface, it may produce an electromotive force(e.m.f) which decreases the electrical resistance of the material.
Photographic films sensitive to infrared radiations can be used to take infrared pictures that reveals hotspots in the landscape.
Infrared detector circuit
Microwaves detections
Microwaves are detected by crystal detectors or solid state diodes. The energy of these wave bands is absorbed by conduction electrons in metals causing electrons to vibrate in the same frequencies as the waves.
Microwave Detector Probe
Radio waves Detectors
Radio waves are detected by aerials or antennae. The energy of radio wave bands is absorbed by the conduction electrons in metals causing the electrons to vibrate at the same frequencies as the waves. The resulting alternating current can be amplified electronically to produce an electrical signals with the same pattern as the radio waves. For maximum sensitivity, the size of the antennae should be of the same order as the wavelength of the radio waves.
An accelerating charged particle produces an electromagnetic (EM) wave. Electromagnetic waves are electric and magnetic fields traveling through empty space with the speed of light c. A charged particle oscillating about an equilibrium position is an accelerating charged particle and if its frequency of oscillation is f, then it produces an electromagnetic wave with frequency f.
Electromagnetic waves transport energy through space which can be delivered to charged particles a large distance away from the source.
Accelerating charges produce changing electric and magnetic fields. Changing electric fields produce magnetic fields and changing magnetic fields produce electric fields. This interplay between induced electric and magnetic fields leads to propagating electromagnetic waves through free space.
Gamma (γ) rays
Gamma rays have the smallest wavelengths and the most energy of any wave in the electromagnetic spectrum.
They results from energy changes occurring in the nuclei of the radioactive atoms.
The term gamma ray was coined by British physicist Ernest Rutherford in 1903 following early studies of the emissions of radioactive nuclei.
They are produced by the hottest and most energetic objects in the universe, such as neutron stars and pulsars, supernova explosions, and regions around black holes.
On Earth they are generated by nuclear explosions, lightning, and radioactive decay.
X-rays
They are produced when a high energy electrons bombard a metal target in an X-ray tube. They are also said to originate from fast moving electrons when they are suddenly stopped by a metal target.
Ultraviolet(UV) Radiation
They are produced by the sun, sparks and mercury vapour lamps due to large energy changes in the electrons of an atom. UV radiation is produced either by heating a body to an incandescent temperature, as is the case with solar UV, or by passing an electric current through a gas, usually vaporized mercury. Electrons in the mercury atoms gain energy from the current then emit it again as UV.
Mercury vapour lamps
Visible light
A visible light stimulus is electromagnetic radiation that can be perceived visually by an organism(Royal Society of chemistry).
Visible light is composed of seven different colours with violet having the least wavelength and red having the highest. It is naturally produced by sun, hot objects, lamps,candles, electric bulbs, laser beams e.t.c.
Visible light is created the same way all other ElectroMagnetic waves are produced from emission of radiation while an electron jumps from an higher energy state to a lower one. In this process all shorts of EM waves are created but we can see only the visible light spectrum.
Illustrating visible light
Infrared Radiation(IR)
It is produced as a result of small energy changes of an electron in an atom or molecular vibrations which happens in the sun, fire or any hot objects.
Any material with temperature above absolute zero emits InfraRed and so IR radiations are produced in all matter by means molecular vibration. Molecular movement causes infrared emission of different wavelengths and frequencies but each wave is proportional to the temperature of the body where higher the temperatures produces radiations of higher frequency and hence with shorter wavelengths.
Microwaves
They are produced by special vacuum tubes called magnetrons in microwave ovens or with a maser that operates on the ballistic motion of electrons controlled by magnetic or electric fields
Microwaves are produced by special vacuum tubes like the klystron, magnetron and Gunn diode where the frequency of microwaves is selected to match the resonant frequency of motor wall so that the energy is transferred efficiently to the kinetic energy of the molecules.
Microwave production
Radio Waves
Radio waves are produced artificially by time-varying electric currents, consisting of electrons flowing back and forth in a specially-shaped metal conductor called an antenna. An electronic device called a radio transmitter applies oscillating electric current to the antenna, and the antenna radiates the power as radio waves.
Radio waves are received by another antenna attached to a radio receiver. When radio waves strike the receiving antenna they push the electrons in the metal back and forth creating tiny oscillating currents which are detected by the receiver. see the illustrations below
I value freedom. Colonized nations fought for freedom and citizens in democratic nations pride themselves in some kind of freedom.
But you can have freedom but still not free. You can have freedom to do one thing but lack it in something else.
When we say we are free, are we free indeed.?
Types of freedom includes
Financial freedom
This is when we have enough money so that nothing that requires money that we can be restricted from. It is freedom to have whatever we desire because we can be can afford it. You may not be in prison walls but you are life is soo restricted because of being broke or poor. You cannot move even though you have freedom to move whenever you many want because you lack resources to do that. Financial freedom keeps people from attaining their desires just like people locked behind bars crave for freedom. I remember in my days of small beginnings how I desired to join some schools and get education but all I could have are desires, I could just watch the institutions walls from a distance but could not go there because I was poor. I was a prisoner of desires I could never attain just the way prisoners look at people with freedom of movement but cannot go anywhere because they are locked.
Other types of freedom includes:
Speech freedom
This is a privilege enjoyed by citizens of democratic societies or nations where they can express their thoughts and opinions without being judged harshly
Physical freedom
This is where we are not restricted in movement and we can travel or go where we need to go . But I think physical freedom is connected to financial freedom because without money you can only be able to go to only limited places.
Spiritual freedom
It is when you have peace in your soul and you are not haunted by things like guilt, anxiety or tormented by things beyond your control
Mental freedom
Ability to think clearly and have clarity of thoughts. It is where you have power to imagine and have the means to test your thoughts.
Political freedom
Ability to express your political views without intimidation , coercion or persuasion.
Academic freedom
Protection from undue influence or pressure from academic institutions, governments, or external organizations that may seek to limit or control academic inquiry and expression.
However If you have financial freedom, you can be able to purchase physical freedom as well ,,,so I think …….🤔
The electromagnetic (EM) spectrum is the range of all types of Electromagnetic radiation. Radiation is energy that travels and spreads out as it goes – the visible light that comes from a lamp in your house and the radio waves that come from a radio station are two types of electromagnetic radiation.
Electromagnetic waves are transverse waves which results from oscillating electric and magnetic fields at right angles to each other.
When all the electromagnetic spectrum are arranged in order of their wavelength or frequency, they form what is refered to as the electromagnetic spectrum.
A complete spectrum is shown below:
The figure below shows electromagnetic waves arranged in order of decreasing wavelengths
Properties of Electromagnetic waves
Electromagnetic waves have the following common properties.
They travel through vacuum(space) with a speed of 3.0 x 10-8ms-1 . This speed is usually refered to as the speed of light in vacuum and is usually denoted by c.
They do not require material medium for transmission
They are transverse in nature
They undergo interference, reflection,refraction and polarisation effect
They posses energy in different amounts according to the relation E=hf where h is the Plank’s constant given as 6.63 x 10-34 Js and f is the frequency
They carry no charge
They are not affected by electric or magnetic fields
Example: calculating energy of a wave
A certain electromagnetic radiation was found to be having a wavelength of 6.5 x 10-8 m. Calculate the energy it emits.
solution
to calculate energy of a wave, you need to know about it’s frequency and then multiply the frequency with the planck’s constant.
we have only the wavelength only but we can get the frequency from the relation: v = fλ
since it is an electromagnetic wave, it’s speed is 3.0 x 10-8 ms-1. and hence f=v/λ. that is:
=4.6154 x 1015 HZ
The energy of a wave was defined as E = hf where h (plank’s constant)= 6.63×10−34 Js
hence E = 6.63 x 10-34 Js x 4.6154 x 1015 HZ≈ 3.06 x 10-20J
Mutual induction is a phenomenon in physics where a changing magnetic field in one coil of wire induces a voltage across another nearby coil. When the magnetic field passing through one coil changes, it induces a voltage in the other coil, according to Faraday’s law of electromagnetic induction.
This principle is fundamental to the operation of transformers, where two or more coils of wire are used to transfer electrical energy from one circuit to another by means of a changing magnetic field.
Mutual induction is a key concept in the functioning of many electrical devices and is utilized in various applications, including power transmission, signal coupling, and wireless power transfer.
Demonstrating mutual Induction
To investigate mutual induction, set two coils close to each other as shown
Using the variable resistor, put the current to minimum and observe the behavior on the galvanometer from the following actions:
closing the switch K
opening the switch K
Increasing the current using variable resistor when the switch is closed
decrease the current using variable resistor when the switch is closed
replace the D.C power supply with A.C power supply.
Observations
when the switch K is closed, the pointer deflects in one direction and then comes back to zero. When K is opened, the pointer deflects to the opposite direction and then falls back to zero.
Increasing current in the primary coil causes deflection while decreasing it causes deflection to the opposite direction.
If direct current (d.c) is replaced with an alternating current source, the pointer of the galvanometer vibrates continously about the zero point.
Explanations
When the switch is closed, the current in the primary coil increases from zero to maximum value within a very short time and so the magnetic flux in the primary coil linking with the secondary coil increases from zero to maximum at the same interval of time inducing an e.m.f in the secondary coil.
The induced emf in the secondary coil causes flow of current hence deflection on the galvanometer.
The induced e.m.f lasts only for a period where current is transiting from zero to maximum and so the pointer on the galvanometer returns to zero after a very short time. This is because after the current in primary coil builds up to it’s maximum value, there is no further change in magnetic flux in the primary coil and so induced e.m.f in the secondary coil stops.
When the switch is opened, the current in the primary coil takes a very short time to fall from maximum to zero hence the magnetic flux in the primary coil linking with the secondary coil also falls from maximum value to zero inducing an e.m.f in the secondary.
The current in the circuit takes much shorter time to fall off from maximum to zero than it takes to build up from zero to maximum and therefore induced e.m.f is much higher when current is being switched off than when it is switched on.
When the current is increased continously, the magnetic flux in the primary coil which links with the secondary coil also increases at the same rate causing an e.m.f to be induced in the secondary.
When current in the primary is decreased continously, an e.m.f is induced in the secondary due to the decreasing magnetic flux of the primary coil linking with the secondary coil
The direction of current in the secondary coil is to the opposite direction to that of primary coil so that the polarities in the secondary and primary coil are such that they oppose each other. The direction of current on each coil can be determined by Lenz’s law.
When the switch is closed and current is building up, the direction of current in primary and secondary coil is as illustrated below:
when the current is decaying after switch is opened, the direction of the induced e.m.f in the secondary coil is as shown.
most often the e.m.f induced in the secondary coil is less than what was produced in the primary coil. This is mostly because of what is called flux leakage where all the magnetic flux from primary coil does not link with the secondary coil.
The induced e.m.f in the secondary coil can be increased by ensuring more flux from primary coil are linking with the secondary coil.Some of the techniques used includes:
i. Winding primary and secondary coil on a soft magnetic flux
In this method, the primary and secondary coil are linked together on one soft iron which helps to concentrate magnetic flux in both coils. Typical arrangement is as shown.
In the above arrangement, both primary and secondary coil are wound on the same iron core.
ii. Both secondary and primary coil on same soft iron ring
Magnetic flux tends to form circular loop and so a circular ring makes them work better . The arrangements is as illustrated.
The ring enables all the magnetic flux of the primary to form concentric loops within it thus reaching the secondary coil more efficiently.
iii. Having more turns in the secondary coil
we saw earlier that the total induced e.m.f in the coil is the summation of all the e.m.fs induced by individual turns in the coil. When there are more turns in a coil, it then means there will be more e.m.f in that coil. Consider the setup illustrated below.
The e.m.f is induced in each turn of the secondary coil since the magnetic flux of the primary coil links with each .
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