Tag: physics

The formula for velocity, when given wavelength and the frequency of the wave, is written as: $v=f\lambda $.
In this formula, $f$ represents frequency, $v$ represents the velocity of the wave, and $\lambda $ represents the wavelength of the wave.  
Here, the frequency of the wave is $500 MHz = 500000000 Hz$  and the wavelength is $60 cm = 0.6 m$
Hence, the velocity of the wave is $3\times { 10 }^{ 8 }m/s$.

In the order of increasing wavelength, the waves are Gamma rays ($< 1 nm$), X-rays ($1-10 nm$), infrared rays ($700-{ 10 }^{ 5 }nm$), micro waves (${ 10 }^{ 5 }-{ 10 }^{ 8 }nm$), radio waves (${ >10 }^{ 8 }nm$).
Hence, the radiations of wavelength just longer than ${ 8\times 10 }^{ -7 }m$ is Infrared.

Fraunhofer spectral lines are also called line absorption spectra. They are a set of spectral lines. The lines were originally observed as dark features (absorption lines) in the optical spectrum of the Sun.

Generally, three types of radiation come from the sun to Earth, they are, ultraviolet radiation, visible light, and,  infrared radiation. Out of these three radiations, ultraviolet radiation is prevented by the ozone layer and visible light and high-frequency infrared radiation reach to earth, because they can pass through the atmosphere of the Earth.

The frequency of $\gamma-$ rays is more than that of X-rays.

Cosmic rays are coming from outer space, having high energy charged particles, like $\alpha$-particle, proton etc. 

Infrared radiations are used as a part of thermal therapy. Thermal therapy is widely used for increasing the extensibility of the collagen, to decrease the joint stiffness, to relieve the muscle spasms, to increase the flow of the blood.

$\beta$ -rays are streams of electron and cosmic rays are waves coming from space. So they are not electromagnetic waves.

All of the options are uses of UV Radiations. 

EM waves travel with the same speed in vacuum (or air) which is same as the speed of light ie. $\displaystyle 3\times { 10 }^{ 8 }m/s$