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Notes, Exercises, Videos, Tests and Things to Remember on Electromagnetic Waves

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## Note on Electromagnetic Waves

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#### Electromagnetic waves

Electromagnetic waves are the waves which carry energy by the variations of electric and magnetic fields. Infrared radiation, visible light, and ultraviolet radiation are examples of Electromagnetic waves.

##### Visible light

Visible light is defined as the form electromagnetic radiation or wavelength that are visible to human eye. Visible lights are produced by flames and discharge tubes. Wavelength of visible light ranges from 4$$\times$$ 10-7m to 8 $$\times$$ 10-7m. Long wavelength visible light is red light with 8 $$\times$$ and short wavelength visible light is violet with 4 $$\times$$ 10-7m. The frequency range of visible light is between 400 to 790 THz. Visible light is used in communication.

It is a form of electromagnet radiation which is invisible to human eye. The wavelength of infrared radiation ranges from 10-5m to 5 $$\times$$ 10-3m. We cannot see infrared radiation but we can feel due to its heat. The frequency range of infrared radiation is between 430THz to 300GHz. Infrared is used in night vision where the is not enough light. It is also used in tracking, heating, and communication. Sun also produced infrared radiation. We cannot see them as they are invisible but we feel hot or warm due the infrared radiation of the sun when we stay in sunlight.

Radio waves is a type of electromagnetic radiation. It is widely used in communication, in television, cell phones, radios, etc. It is used in the transmission of data in coded form. In the form of radar, it is used also for sending out signals and picking up their reflections from objects in their path. It has the longest wavelength among all the electromagnetic spectrum. The wavelength of radio waves ranges from 10-4m to 5 $$\times$$104m. It is produced by electrical oscillations and is detected by radio receivers or similar tuned circuits. The frequency of radio waves ranges from 300GHz to 3Hz.

Ultraviolet radiation is a form of electromagnetic radiation with wavelength ranging from 5 $$\times$$ 10-9m to 5 $$\times$$ 10-7m. It has a shorter wavelength than visible light but longer than X- rays. It is present in the sun. It stimulates vitamin D production in our body but is harmful to eye and skin. In ozone layer, it produces ozone gas. UV radiation is widely used in industrial processes and in medical and dental practices for a variety of purposes, such as killing bacteria, creating fluorescent effects, curing inks and resins, phototherapy and suntanning.
##### X- rays andγ- rays
X- rays andγ- rays are electromagnetic radiation like radio waves, infrared radiation, ultraviolet radiation, etc. The wavelength of X-rays andγ- rays ranges below 5 $$\times$$ 10-8m. They are high energy electromagnetic radiation or are of high frequency.γ - rays are produced in radioactive decay and nuclear reaction. X- rays are produced by electrons. X- rays are used in hospitals for medical purpose. Gamma rays are used in medical field to cure cancer.
##### Difference between ultraviolet rays and x-rays
 Ultraviolet rays X-ray Its average wavelength and frequency are 10-8 and 1015 Hz respectively. Its average wavelength and frequency are 10-10 and 1018 Hz respectively. It is obtained from sun, tube light etc. It is obtained by x-ray machine.
##### Difference between ultraviolet rays and infrared rays.

 Ultraviolet rays Infrared rays The frequency is high. The frequency is low. They have more energy. They have less energy. They are harmful. They are not harmful.

• Electromagnetic waves are the waves which carry energy by the variations of electric and magnetic fields.
• Visible light is defined as the form electromagnetic radiation or wavelength that are visible to human eye.
• . The wavelength of infrared radiation ranges from 10-5m to 5 $$\times$$ 10-3m.
• Ultraviolet radiation is a form of electromagnetic radiation with wavelength ranging from 5 $$\times$$ 10-9m to 5 $$\times$$ 10-7m.
•  The wavelength of X-rays andγ- rays ranges below 5 $$\times$$ 10-8m.
• X- rays are produced by electrons. X- rays are used in hospitals for medical purpose. Gamma rays are used in medical field to cure cancer.
.

### Very Short Questions

The process of splitting up of white light into seven visible colors is known as dispersion of light.
The dispersion of light can be seen through prism, in rainbow, soap bubbles, etc.

The speed of all colors in vacuum is same. When the white light enters a denser medium the speed as well as wavelength of each color decreases and they separate with each other. On leaving the medium, its speed increases than its original value. The red light has the maximum speed whereas the violet light has the minimum speed within the denser medium.
So, red light deviate the least and violet light deviates the most and other colors lie between red and violet. It is the cause of dispersion.

The prism has triangular shape. When a beam of light enters the face AB of prism, it gets refracted towards BC and strikes the face AC. When the rays enter to air from glass, they further separate with each other. Hence, a prism disperses a white light.

The two opposite surfaces of glass slab are parallel with each other. The surface AB refracts a beam of light and produces a spectrum of seven colors. When these colors strikes the surface CD, then all the color get mixed up and white light emerged out to the air again. This is why light is not dispersed on passing through a glass slab.

1. The dispersion of light is shown in the figure.
2. The color of ray A is red and color of ray B is violet.
3. It is because its velocity and wavelength are least.
4. Just above A, infrared rays are found and just below the ray B, Ultra violet rays are found.

1. Infrared rays: The rays with longer wavelength than red rays are called infrared rays. These are invisible rays and lies just above the red color on the spectrum. The special characteristic is it is invisible.
2. Ultraviolet rays: The rays with shorter wavelength than that of the violet rays are called UV rays. They are also invisible and lie just below the violet color in the spectrum

Two advantages of the ultraviolet rays are as follows:

1. It destroys the bacteria of air.
2. It converts ergosterol hormone of our skin into vitamin D which is necessary to our body.
Two disadvantages of the ultraviolet rays are as follows:
1. It burns our skin and makes it black.
2. Excess of UV rays destroys the retina of our eyes which causes blindness.

1. The level of the mercury on the thermometer rises when it is placed above ray 1 because there lies infrared rays and it has more heat energy.
2. A beam of light enters to a prism and gets refracted. The spectrum so formed by the prism passes through an inverted prism and all colors get mixed up. At last, white light is emerged out from the prism. So, in this case, dispersion does not occur.

 Mechanical wave Electromagnetic wave Mechanical waves are the disturbance that require a material medium to propogate. Eg: sound waves Electromagnetic waves are the waves in which the variation of electric and magnetic field takes place during their propagation.Eg: light waves They cannot transmit without medium They can transmit without medium.

The electromagnetic waves are classified according to their wavelength or frequency. The range of wavelength or frequency of electromagnetic waves is called electromagnetic spectrum.

The main properties of electromagnet are as follows:

1. They are transverse wave.
2. They are unaffected by electric and magnetic fields.
3. They follow the laws of reflection and refraction.

 X-rays Infrared rays They have shorter wavelength They have longer wavelength. They have high penetrating power. They have low penetrating power. They are harmful to our body. They are not harmful.

The light waves with wide range of wavelengths (10-5m to 5 x 104m) and lie on the spectrum just beyond the infrared region is called radio waves.
The radio waves are not harmful to our body because they have longer wavelength and very low frequency and have less penetrating power.

The uses of x-rays and y-rays are as follows:

1. To observe internal organs of the body
2. To kill dangerous cancer cells and tumors in the body

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• ### How does a pencil put in a beaker full of water appear?

Short and bent
Very wet
opaque due to refraction
shiny
• ### What happens to a coin inside a beaker of water?

It appears closer to surface than it really is
It's position is horizontally shifted due to refraction
Reflection makes it appear shorter than usual
It appears more shiner than outside due to refraction

VIYGBOR
VIBGYOR
VIGYBOR
VIBYGOR

Indico
Indigo
Indica
Indigu
• ### The light spectrum is arranged from Violet to Red so to represent

Light of high speed to light of low speed
Very bright light to very dim light
Very dim light to very bright light
Light of low speed to light of high speed

Green
Violet
Blue
Red

Blue
Orange
Green
Violet
• ### The main cause of dispersion of light through glass prism is

Difference in optical density of various light in the glass
Difference in luminosity of various light in the glass
Difference in speed of various light in the glass
Difference in intensity of various light in the glass
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Prisms are used in binoculars

Sky is blue