Tag: electromagnetic spectrum

Questions Related to electromagnetic spectrum

The rms value of the electric filed of a plane electromagnetic wave is 720 V/m.The average energy density of electric field and the average energy density are 

physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

  1. $4.58*{ 10 }^{ -6 }{ Jm }^{ -3 };2.15*{ 10 }^{ -7 }{ Jm }^{ -3 }$

  2. $4.3{ 10 }^{ -7 }{ Jm }^{ -3 };8.6{ 10 }^{ -7 }{ Jm }^{ -3 }$

  3. $2.15{ 10 }^{ -7 }{ Jm }^{ -3 };4.3{ 10 }^{ -7 }{ Jm }^{ -3 }$

  4. $8.6{ 10 }^{ -7 }{ Jm }^{ -3 };4.3{ 10 }^{ -7 }{ Jm }^{ -3 }$

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Correct Option: A

The solar spectrum is -

physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

  1. Continuous

  2. Line spectrum

  3. Spectrum of black lines

  4. Spectrum of black bands

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Correct Option: A

The following can be arranged in decreasing order of wave number
A. AM radio
B. TV and FM radio
C. Microwave
D. Short radio wave

physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

  1. A > B > D > C

  2. C > D > B > A

  3. A > B > C > D

  4. D > C > B > A

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Correct Option: B

A welder wears special glasses to protect his eyes mostly from the harmful effect of 

physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

  1. Very intense visible light

  2. infrared radiation

  3. ultraviolet rays

  4. microwaves.

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Correct Option: C
Explanation:

During the welding process, the ultra-violet rays are produced which are not visible but have an intense effect on the eyes. Therefore, the welder makes use of the special glass to protect his eyes.

Option (C) is correct.

The wavelengths for the light of red and blue colours are roughly $7.8\times 10^{-7}m$ and $4.8\times 10^{-7}m$ respectively. Which colour has the greater speed in vacuum?

physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

  1. Red

  2. Violet

  3. Yellow

  4. All colors have same speed

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Correct Option: D
Explanation:

All electromagnetic waves travels at the same speed in vacuum i.e $3\times10^8$ m/s. Due to the absence of matter, there is no change in speed corresponding to wavelength. There is no absorption and re-emission of light in the absence of matter.

An electromagnetic wave has a frequency of $500MHz$ and a wavelength of $60cm$. Name the medium through which it is traveling.

physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

  1. air

  2. water

  3. salt

  4. cardboard

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Correct Option: A
Explanation:

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 $60 cm = 0.6 m$
Therefore, the velocity of the wave is $3\times { 10 }^{ 8 }m/s$.
This determined velocity is the velocity of the light in air. Hence, the medium through which the wave is travelling is air.

Two waves $A$ and $B$ have wavelength $0.01A^o$ and $9000A^o$ respectively. Compare the speeds of these waves when they travel in vacuum.

physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

  1. $1:9$

  2. $9:1$

  3. $1:1$

  4. None of the above

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Correct Option: C
Explanation:

The electromagnetic spectrum consists of the full range of known electromagnetic waves, including gamma rays, X-rays, ultraviolet light, visible light, infrared light, microwaves, and radio waves. All of these are produced by various forms of oscillating charges or currents. Electromagnetic waves are transverse waves which travel at the speed of light and involve oscillating electric and magnetic fields at right angles to each other.
Hence, the speeds of these waves when they travel in vacuum is same as the speed of visible light, that is, $3\times { 10 }^{ 8 }m/s$. Therefore, the ratio of their speeds is $1:1$.

High energetic radiations among the following:

physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

  1. $\lambda=0.01 A $

  2. $\lambda=0.10 A $

  3. $\lambda=1.00 A $

  4. $\lambda=40.0 A $

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Correct Option: A
Explanation:

We know that, $E = hv = \dfrac{hc}{\lambda}$
Hence highest energetic rediation is whose wavelength is atleast i.e $ \lambda = 0.01 A^{\circ}$

All components of the electromagnetic spectrum in vacuum have the same

physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

  1. energy

  2. velocity

  3. wavelength

  4. frequency

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Correct Option: B
Explanation:

$Answer:-$ B 

speed of electromagnetic wave in vacuum  is given by:-
c(speed of light)=frequency$\times$ wavelength =$\dfrac{1}{\mu _0 \epsilon _0}$=constant
as we go from gamma rays to radio waves  frequency decreases and wavelength increases thereby maintaining the product constant.

 Energy is given by:- $E=h\nu$ since $\nu$ is different so energy is also different.
Also wavelength and frequency varies.

Earth's atmosphere is transparent for

physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

  1. only the visible light

  2. only the X-rays

  3. only the $\gamma$- rays

  4. visible light and microwaves

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Correct Option: D
Explanation:

Earth's atmosphere is divided into different layers, out of which the ozone layer absorbs the X-rays and $\gamma$-rays whereas visible light and microwaves are the waves which are not absorbed by any layer of atmosphere.