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# Electromagnetic Spectrum - Practice Questions & MCQ

Edited By admin | Updated on Sep 18, 2023 18:34 AM | #JEE Main

## Quick Facts

• Electromagnetic spectrum is considered one the most difficult concept.

• 47 Questions around this concept.

## Solve by difficulty

For sky wave propagation, the radio waves must have a frequency range in between :

Match List I (Wavelength range of electromagnetic spectrum) with List II (Method of production of these waves) and select the correct option from the options given below the lists.

Match List I with List II

Choose the correct answer from the options given below:

The waves emitted when a metal target is bombarded with high-energy electrons are :

## Concepts Covered - 1

Electromagnetic spectrum

Electromagnetic spectrum-

When we see our surrounding, we see only visible range of electromagnetic waves. So, the only familiar electromagnetic waves were the visible light waves. But, we now know that, electromagnetic waves include visible light waves, X-rays, gamma rays, radio waves, microwaves, ultraviolet and infrared waves. The classification of EM waves according to frequency is the electromagnetic spectrum is shown in the figure given below.

Now we will discuss all these EM waves one by one with the help of following table -

 Type Wavelength range Production Detection Radio >0.1 m Rapid acceleration and decelerations of electrons in aerials Receiver's aerials Microwave 1 mm Klystron valve or magnetron valve Point contact diodes Infra-red 1 mm Vibration of atoms and molecules Thermopiles Bolometer, Infrared photographic film Light to 400 nm Electrons in atoms emit light when they move from one energy level to a lower energy level The eye Photocells Photographic film Ultraviolet 400 nm to 1 nm Inner shell electrons in atoms moving from one energy level to a lower level Photocells Photographic film X-rays 1nm to 10^{-3} nm X-ray tubes or inner shell electrons Photographic film Geiger tubes Ionisation chamber Gamma rays <103 nm} Radioactive decay of the nucleus -do-

Earth's atmosphere -

Earth’s atmosphere has the following six layers.

(i) Troposphere:

The troposphere is the innermost layer of Earth’s atmosphere.i.e it is Closest to the surface of Earth.

It is the thermal classification of the atmosphere.“Tropos” means change. This layer gets its name from the weather that is constantly changing. The troposphere is between 8 and 14 kilometers. This layer has the air we breathe and the clouds in the sky.

(ii) Stratosphere:

The stratosphere is located above the troposphere and below the mesosphere.

It extends between 17-50 Km above the earth's surface. The ozone layer is located in the stratosphere.

Ozone layer - It absorbs most of the ultraviolet rays emitted by the sun.

(iii) Mesosphere:

The mesosphere is located above the stratosphere and below the thermosphere.

It is characterized by temperatures that quickly decreases with increasing height. It extends between 50-80 Km.

(iv) Thermosphere:

The thermosphere is located above the mesosphere and below the exosphere.

Based on the vertical temperature profile in the atmosphere, the thermosphere is the highest layer, located above the mesosphere.

In the thermosphere, temperature increases with altitude.

It extends from about 90 km to between 500 and 1,000 km above our planet.

(v) Ionosphere: It starts at about 75 Km and goes up to 650 Km. It contains ions and free electrons. Aurora occurs in the Ionosphere.

(vi)  Exosphere - The outermost layer of the earth's atmosphere. (640 Km - 1280 Km)

Point to remember -

1. Polarisation in EM wave - For an EM wave, the direction of polarisation is taken to be the direction of the electric field.

2. Wavelength of EM Wave -

$\lambda =\frac{\lambda_{o}}{\mu}$

$\lambda _{o}$ = Wavelength in vacuum

$\mu$ = Refractive index of medium (Detail analysis will be studied in Optics)

## Study it with Videos

Electromagnetic spectrum

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