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.
Electromagnetic spectra are arranged in order of their wavelength or frequency. This arrangement forms what is known 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
The Electromagnetic waves have the following common properties.
They travel through vacuum(space) with a speed of 3.0 x 108ms-1 . This speed is usually referred to as the speed of light in vacuum and is usually denoted by c.
Do not require material medium for transmission
They are transverse in nature
Electromagnetic waves undergoes interference, reflection,refraction and polarisation effect
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 the energy of a wave, you need to know its frequency. Then multiply the frequency by Planck’s constant.
Here we have only the wavelength, 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.
Wave is a form of energy. Wave energy is useful as well as dangerous to human beings. Communication technology uses concept of waves as its fundamentals. Earth quakes are as a result of seismic waves resulting from shifting of locks within the earth.
Phenomenon’s like formation of rainbows formation, mirages and thin films in oil shows presence of waves. Variations in quality of sound from musical instruments is based on the properties of waves.
Wave properties can be investigated by use of a ripple tank. Waves exhibits various properties that can be conveniently illustrated using a ripple tank.
The ripple tank
Ripple tank helps us study properties of water waves. Studying water waves can help us explain the characteristics of other types of waves such as light and sound waves.
Ripple tank consists of:
a transparent tray containing water
a point source of light above the tray
white paper screen and
an electric motor.
The white screen is underneath the tray while the electric motor is on the surface of the water in the tray. The figure below shows the basic structure of the ripple tank.
The water waves are the ripples traveling across the surface of the shallow water in the tray . This ripples are produced by the vibrations of the electric motor.
When you deep a finger in water, a pulse of wave is usually produced. This circular wave radiates outwards from the source of disturbance. This pulse in water is called a ripple. water ripples are progressive as they continuously propagate away from the source.
How ripple tank is used
A generator enables generation of continuous ripples. The electric motor is mounted on a wooden bar on a ripple tank. When the motor is started, the bar is made to vibrate by an electric metal disc on the axle of the motor.
To generate continuous straight waves, the length of the bar is adjusted so that it just touches the water surface. To generate continuous circular waves , a small ball called a dipper fitted to the bar is adjusted so that it just touches the water surface.see the figure below:
The figure below shows circular and line waves:
When the light from the lamp passes through the waves , the images of the waves are projected on the paper underneath.
Since the bottom of the tray is transparent, the light casts an image of the passing waves on the screen. When light from the lamp is passing through the water, the curve of the water surface acts like a series of lenses. These lenses are both converging and diverging that focus light to create a series of bright and dull lines. The wave crests produce bright lines while troughs produce dark lines. see the figure below.
To cut down unwanted reflections, the sides of the tray is aligned with spongy material.
For easier observations of the progressive waves, a stroboscope is used.
Stroboscope
A stroboscope is a disc with equally spaced slits which can be rotated by hand or a motor. If the speed of rotation is such that the wavefront advances one wavelength each time a slit passes through the eye, the wave fonts appears to be stationary. The waves are then said to be frozen.
Another type of stroboscope is made up of a lamp which flashes light on and off at a controllable measurable rate. At a frozen motion, the successive appearance of the slits at a particular point matches exactly with the period of the wave. this gives persistence of vision as the eye receives glimpses of the waves at the same level of displacement each time. The figure below illustrates observation of water waves through a stroboscope.
The wave pattern is represented by wavefronts lines that connects all the points that are in phase as the wave progresses. It follows that the distance between successive wave-fronts is equal to one wavelength.
Vocabulary of waves
oscillation
Also known as vibration. oscillation is when a wave makes one complete cycle of to and fro motion about the mean position.
the figure below illustrates a wave making one oscillation:
Amplitude
It is the maximum displacement of a particle from its rest position.
wavelength
This is the distance between two successive particles which are in phase and are moving to the same direction.
Frequency f
This is the number pf oscillations made by the wave in one second.
The term “properties of cathode rays” refers to the various physical characteristics and behaviors observed when cathode rays are studied under different conditions.
properties of cathode rays includes:
They travel in a straight line
They cause fluoresce or glow to certain materials
they are charged
They possesses kinetic energy
pass through thin materials, demonstrating their ability to penetrate objects to varying degrees depending on the material’s density and the energy of the rays.
ionize gases
The charge-to-mass ratio of cathode rays (electrons) is relatively high. A property used to identify the electron and distinguish it from other particles.
Deflection by Magnetic Fields
Showing that cathode rays travels in a straight line
When an opaque object is placed between the screen and the cathode in the path of the cathode rays, a sharp shadow is cast on the screen.
Cathode rays causes certain substances to glow or fluoresce
Fluoresce materials are materials that glows when electromagnetic energies falls on them. such materials includes zinc sulphide, Fluorescein, Rhodamine, Coumarin, Acridine Orange and Quantum Dots.
when cathode rays falls on screen coated with the fluoresce materials, the fluoresce material glows.
showing that cathode rays are charged
Cathode rays are deflected by both magnetic and electric fields.
Inside the magnetic field, the cathode rays are deflected towards the positive plate showing that they are negatively charged. Remember that opposite charges attract while while same charges repel from the basic law of charges. see the figure below:
When cathode rays passes through magnetic field, they are deflected in the direction determined by Fleming’s left-hand rule. The deflection in magnetic field shows that they are negatively charged as shown in figure below.
Cathode rays have kinetic energy
The deflection of cathode rays in a magnetic field shows they are moving, and therefore possess kinetic energy. By measuring how much the cathode rays bend in the magnetic field, you can calculate their velocity. Using the velocity, you can compute the kinetic energy of the cathode rays.
When cathode rays are suddenly stopped by a metal target, they can produce x-rays. This confirms that they are actually a stream of fast moving electrons.
Exam Questions on properties of cathode rays
Figure 14 shows a cathode ray tube. A metal plate is placed between the anode and the screen.
(I) State with reason what would be observed on the screen when the cathode rays are produced. (2 marks)
(ii) State the effects on the cathode rays produced when the anode is increased. ( 2 marks)
An alternating current generator is also known as an alternator. A generator is a device or machine that converts mechanical energy energy into electrical energy by rotating conductors through magnetic fields.
Figure below illustrates a simple generator made of curved permanent rectangular magnetic poles, slip rings, conductor made into a loop and carbon brushes.
The poles of magnets are curved so that the magnetic field is radial. Current enters and leaves the coil through the brushes which are pressing against the slip rings.
Carbon brushes are preferred because they are good conductor, slippery to allow the wire slide along with ease and acts as a lubricant.
The a.c Generator
The ac generator will produce electric current in the coil when the coil rotates through magnetic field using the principle of electromagnetic induction.
When the coil rotates clockwise as indicated on the diagram at the rotation axis, edge AB rotates upwards while CD rotates downwards causing the two edges cuts the magnetic field at right angles while at the horizontal position. The induced e.m.f is maximum when the coil is perpendicular the the magnetic field.
Using the Fleming’s right-hand rule, the flow of current is in direction A-B-C-D when the direction of rotation is clockwise. The induced current flows through the external circuit via the slip rings and through carbon brushes.
As the coil rotates from horizontal to vertical position, the angle at which the sides of the coil cuts the magnetic field reduces from 90o to 0o causing the induced e.m.f reduces from maximum value (Eo) to zero e.m.f. when the coil becomes positioned vertically
An overview of the cross-section of the coil in a magnetic field is shown below.
At the instant when the coil is rotating past the vertical position, the sides AB and CD is moving parallel to the field and that position the coil do not cut the magnet field and therefore the induced e.m.f is zero at that position.
Past the vertical position, side AB and CD exchanges position .Side AB starts moving downward and CD upward. The angle at which the sides of the coil cuts the magnetic field increases from 0o to 90o when the coil comes back to horizontal position.
When the angle is increasing from zero to 90o , the induced e.m.f increases from zero to maximum value Eo. When AB and CD exchanges positions in the coil rotation, the direction of current flow reverses to D-C-B-A making brush y positive and brush x negative.
As the coil rotates further to complete one revolution, the angle at which its sides cuts the magnetic field reduces from 90o to 0o and the e.m.f induced in the coil reduces from maximum value Eo to zero.
Variation of current in an a.c generator
The variation of the e.m.f increases from zero to maximum at one quarter cycle before reducing from maximum to zero at the next quarter circle and then starts increasing to maximum value in the negative direction in the third cycle. At the fourth cycle, it increases from maximum negative value to zero. Thus, in one complete oscillation of the coil, the variation of induced e.m.f against the angle of rotation forms a sinusoidal curve. The curve formed by this variation can be represented by the equation:
E = Eo sin θ
where E is an instantaneous e.m.f at any particular angle of rotation where Eo is the maximum e.m.f and θ the angle between plane of the coil and the vertical axis.
The formation of the sine curve is as illustrated
By ohms law, I = E/R where R is the resistance of the circuit and I is an instantaneous current at random position of ration of the coil.
Therefore I = (Eo/R) sin θ
A typical graph of e.m.f against the angle θ is as illustrated
After one complete circle, the rotation pattern repeats itself and many circles are made per unit time. The number of cycles made per second is referred as the frequency of the generator and is also the frequency of the a.c current.
Most of generators used to make commercial power productions makes 50-60 revolutions per second. In USA, the frequency is 60Hz while in Europe and Asia, it is usually 50 Hz.
Magnetic field is a region around the magnet where the magnetic force is experienced.
Magnetic field is represented by lines called magnetic field lines which also show direction of the magnetic field.
Direction of magnetic force is the direction to which a north pole of a magnet would move when set to freely move.
Properties of magnetic field lines
Magnetic field lines must not cross each other but always flows parallel to each other. They repel each other and forms closed paths.
At the middle of a bar magnet, which is the midpoint of the separation of the two poles of a magnet, there exists no magnet field as there is no magnetic field lines passing there. Such a point is usually referred to as the neutral line.
A neutral point in a magnetic field is the point where the magnetism due to like poles cancels each other.
The poles of a magnetic have the highest concentration of the magnetic field lines hence the strongest magnetic force.
The stronger the magnet, the closer the field lines.
If the magnetic field lines are parallel and equally spaced , then the magnetic field is said to be uniform.
The direction of magnetic field lines is such a way that they run from north towards the south outside of the magnet and from south to north inside the magnet as shown.
They are equations that shows the relationship between ratio of turns in secondary to primary coil and the ration of their voltages and consequently the current.
The first equation states that:
similarly, for an ideal transformer where no energy loss is experienced, the power in primary coil = power in secondary coil
Electrical power P is given by ; P = Current I x Voltage V
Let Ip =current in primary coil and Is = current in secondary coil
Then we have :
primary current x primary voltage = secondary current x secondary voltage
To verify Hooke’s Law, you can conduct a simple experiment using a spring and weights and follow the steps below.
Apparatus
A spring (helical coil spring)
A support stand or clamp
A ruler or measuring tape
Weights (e.g., metal washers or masses)
A balance or scale (optional, for measuring weights)
Procedure:
set the apparatus as shown
One end of the spring is securely fixed to a support stand or clamp, ensuring that the spring hangs vertically without touching any surfaces.
The length of the spring is determined by reading the pointer position on the ruler fixed besides the spring as in the figure below. This will serve as the reference length 𝐿0=_______________
We Start by attaching a small weight of like 50g (0.5N) to the free end of the spring as shown.
We record the weight of the added mass 𝑚 in kg. The weight should be small enough to avoid damaging the spring but large enough to cause noticeable stretching.
With the weight attached, we measure and record the new length of the spring and then subtract the initial length 𝐿0 from the stretched length L to find the extension e
Record the extension found from e=L-𝐿0
We increase the load and record the corresponding extension in each case so as there is a table showing extensions given by different forces on the spring. The table is similar to the one shown below.
A graph of force F against the extension per each force resulting to a straight line through the origin as shown below:
Notes:
Ensure that the spring is not stretched beyond its elastic limit, as this can cause permanent deformation and invalidate the results.
Repeat the experiment multiple times to ensure accuracy and reliability of the measurements.
Use a balance or scale to measure weights accurately, and be cautious when handling heavy objects to prevent accidents.
Observations
Provided the stretching weight is not too much, the spring always return to it’s original length when weight is unloaded.A plot of stretching force against extension is a straight line through the origin showing that the ratio of force against extension is a constant.
Explanations
Extension of a spring is directly proportional to the stretching force F. The stretching force can be exceeded beyond a certain value that causes permanent stretching that does allow return of original length on unloading.
The graph of extension against stretching force is as shown.
OP represents the permanent stretching or permanent extension of the spring.
Point E is known as the elastic limit of the spring. Beyond the elastic limit , further extension causes permanent extension.
Hooke’s law
This is a law that was developed by Robert Hooke after he investigated principles behind stretching of materials under forces and concluded his findings in Hooke’s law that states that:
For a helical spring or other elastic material, the extension is directly proportional to the stretching force provided the elastic limit is not exceeded.
The Hooke’s law cab be represented with mathematical notations as:
Force F ∝ extension e;
From the relationship above, an equation is developed such that:
F = ke where k is a constant of proportionality which depends on the material making the spring. The constant k is usually referred to as the spring constant.
k is obtained from the plotting of F against e as the gradient of the graph as shown below
That is;
gradient = k = change in force/ change in extension
The spring constant is expressed in Nm-1 as it’s SI units.
Remember that some work is done whenever a force moves some distance s. that is; work = Fs.
Therefore, work is done by force when spring extends by distance e. The total work done by the masses stretching the spring is the average the work done by individual mass and can be obtained as area under the graph of force F against extension e.
The area under the graph is definitely the area of a triangle which will be obtained as work done = (1/2)Fe where F is the force applied and e is the extension produced by the force.
but F = ke and so we can substitute F for ke so that we have :
Questions for practice
A mass of 100g is suspended from the lower end of a spring . If the spring extends by 100 mm and the elastic limit of the spring is not exceeded, what is the spring constant.
Answer: 10 Nm-1
2. A metal cube suspended freely from the end of a spring causes it to stretch by 5.0 cm. A 500 g mass suspended from the same spring stretches it by 2.0 cm. If the elastic limit is not exceeded:
(a) Find the weight of the metal cube (answer: 12.5 N)
(b) By what length with the spring stretch if a mass of 1.5 kg is attached to it’s end? (answer: 6.0 cm)
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.
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