Physics

Electromagnetic Waves and Spectrum

659 Questions

Electromagnetic waves and spectrum questions test a candidate's understanding of radiation frequencies, wavelengths, and the properties of different rays like infrared, ultraviolet, and visible light. Concepts also cover practical applications in astronomy and the fundamental speed of light calculations. This physics topic appears regularly in general science sections of major competitive examinations.

UV rays propertiesElectromagnetic radiation frequencyWavelength identificationSpeed of light calculationsBlack body radiation

Electromagnetic Waves and Spectrum Questions

Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

Radiations used to get relief from bodyaches are:

  1. I.R. radiations

  2. U.V. radiations

  3. visible radiations

  4. none of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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.

Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

Electromagnetic waves of wavelength ranging from $100\mathring{A}$ to $\mathring{A}$ comes under 

  1. X-rays

  2. UV regions

  3. Visible region

  4. Infrared region
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
X-rays: $10 nm-10 pm\  i.e.\ 10^{-8}m-10^{-11}m$
Given frequency range: $100 \mathring A-  1 \mathring A\ i.e.\ 10^{-8}m-10^{-10}m$
Hence, given wavelength range falls under X-rays
Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

According to the electromagnetic spectrum, radio waves have the ___frequency and the  _______ wavelength.

  1. lowest; largest

  2. lowest; smallest

  3. highest; smallest

  4. highest; largest

  5. medium; medium
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Radio waves are the least energetic waves among other waves. They have the lowest frequency and thus the largest wavelength. Due to this large wavelength character, the radio waves are used in data transmission purposes, since they are hard to interact with particles in the atmosphere.

Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

According to the electromagnetic spectrum, As the frequencies of the pure spectral colours increase, the wavelengths of the colours:

  1. decrease

  2. increase

  3. remain the same

  4. decrease by a factor of 2

  5. increase by a factor of 2
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Speed of all the electromagnetic waves is constant and is equal to speed of light  i.e  $c$

Using        $\lambda \times \nu = c = constant$
$\implies$ If frequencies of the pure spectral colours increase then their wavelength will decrease.

Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

If a particular electromagnetic wave has the highest frequencies among the other electromagnetic waves then it should have the smallest

  1. wavelengths

  2. speeds

  3. amplitudes

  4. energies

  5. periods
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Electromagnetic waves travel with constant speed equal to that of light  i.e  $v =c= constant$

For EM waves       $\lambda \times \nu = c =$ constant
Thus waves with highest frequency will have smallest wavelength.

Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

Find out the wavelength of violet light which has a frequency of $7.5 \times 10^{14}Hz$ ?

  1. $2.25\times 10^{23}m$
  2. $2.5\times 10^{5}m$
  3. $4\times 10^{-7}m$
  4. $7.5\times 10^{-7}m$
  5. $2.25\times 10^{7}m$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Given :    $\nu = 7.5 \times 10^{14}$  Hz

Speed of violet light (EM wave)     $v = 3 \times 10^8$ m/s
Thus wavelength of violet light         $\lambda = \dfrac{v}{\nu}  = \dfrac{3 \times 10^8}{7.5 \times 10^{14}}  =4 \times 10^{-7}$ m

Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

In an electromagnetic spectrum, identify which of the following lists are ordered from longest wavelength to shortest wavelength?

  1. X ray, ultraviolet, visible light

  2. visible light, ultraviolet , X-ray

  3. ultraviolet, X-ray, visible light

  4. ultraviolet, visible light, X-ray

  5. X-ray, visible light, ultraviolet
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Decreasing order of wavelength :

 Visible light > ultraviolet > X-ray
Thus option B is correct.