Electromagnetic Spectrum - Practice Questions & MCQ

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 -              

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)