Electromagnetic Spectrum MCQ Quiz - Objective Question with Answer for Electromagnetic Spectrum - Download Free PDF

Concept:

The relationship between the magnitude of the electric field vector and magnetic field vector of the electromagnetic wave is given by

E₀ = c.B₀

Where c is the Speed of light in vacuum

Calculation:

Given, Electric field amplitude, \({E_0} = 6.3{\rm{\hat j\;V}}/{\rm{m}}\)

The magnitude of magnetic field vector is

\({B_0} = \frac{{{E_0}}}{c}\)

\({B_0} = \frac{{6.3}}{{3 \times {{10}^8}}}\)      [∵ c = 3 × 10⁸ m/s]

B = 2.1 × 10^-8 T

As  is along y-directions and wave is travelling along x-direction. So, \(\vec B{\rm{\;}}\)will be along Z direction.

\(\therefore \vec B{\rm{\;}} = 2.1 \times {10^{ - 8}}\hat k\;T\)

The correct answer is Option 3: A - I, B - II, C - IV, D - III.

Explanation:

X-rays: Frequency range is 10¹⁶ to 10²¹ Hz.

Microwaves: Frequency range is 10⁹ to 10¹¹ Hz.

Radiowaves: Frequency range is 5 × 10⁵ to 10⁹ Hz.

Gamma rays (γ-rays): Frequency range is 10¹⁸ to 10²² Hz.

Concept:

• Electromagnetic spectrum: It is the arrangement of electromagnetic radiations according to their frequency or wavelength.
  • ​The electromagnetic spectrum has a range of frequencies, wavelengths, and photon energies.
  • Typically, electromagnetic waves travel at the speed of light in a vacuum. 
  • The electromagnetic spectrum is as follows: 

​

Explanation:

Concept:

The electromagnetic spectrum consists of all types of electromagnetic radiation arranged according to their wavelength or frequency. As wavelength decreases, frequency and energy increase. The general order from longest wavelength to shortest is:

• Radio waves
• Microwaves
• Infrared (IR)
• Visible light
• Ultraviolet (UV)
• X-rays
• Gamma rays

Explanation:

Among the given options, the electromagnetic waves in decreasing order of wavelength are:

• Radio waves
• Microwaves
• Infrared waves
• Visible light
• X-rays

This order reflects a decrease in wavelength and a corresponding increase in frequency.

The correct option is (3): Radio waves > Microwaves > Infrared > Visible > X-rays

The correct answer is Radio wave.

Key Points

CONCEPT:

Electromagnetic waves or EM waves:

• The waves that are formed as a result of vibrations between an electric field and a magnetic field and are perpendicular to each other and to the direction of the wave is called an electromagnetic wave.
  • The accelerating charged particle produces an electromagnetic (EM) wave.
  • A charged particle oscillating about an equilibrium position is an accelerating charged particle.
  • Electromagnetic waves do not require any matter to propagate from one place to another as it consists of photons. They can move in a vacuum.
  • The electromagnetic spectrum is the arrangement of electromagnetic waves in the increasing order of wavelength.

EXPLANATION:

​

• As we can see in the em waves spectrum, the radio wave has the maximum wavelength.
• Hence option 3 is correct.

Additional Information

Properties of electromagnetic waves:

1. Not have any charge or we can say that they are neutral.
2. Propagate as a transverse wave.
3. They move with the velocity the same as that of light i.e 3 × 108 m/s.
4. It contains energy and they also contain momentum.
5. They can travel in a vacuum also.

Concept:

Electric Field

• The electric force per unit positive charge at a given point is called an electric field. 
• A charge kept static, or in constant motion or accelerated produces an electric field around it which changes with time. 

Magnetic Field

• A magnetic field is the measure of magnetic force at a particular point. 
• A magnetic field is produced by a current-carrying wire which contains charges in motion. 
• So, basically, a charge in constant motion produces a magnetic field around it. 
• When the charge is accelerated the magnetic field varies with time. 

Electromagnetic Wave

• Electromagnetic waves are composed of oscillating magnetic and electric fields.
• The electric field and magnetic field of an electromagnetic wave are perpendicular to each other.
• These waves do not require a medium to travel. EM waves travel at a constant velocity of 3 x 108 m/s in a vacuum.

​

Alpha Beta and Gamma rays

Radioactive decay: 

• When n/p ratio (n is a number of neutrons, p is the number of protons) of an atomic nucleus is high enough to make it unstable, resulting in radioactive decays.
• Radioactive decay mainly emits α- particles, β- particles, and gamma rays.

β-decay:

• It is a type of radioactive decay in which a proton is transformed into a neutron or vice versa inside the nucleus of the radioactive sample. 
• Beta-decay occurs when, in a nucleus with too many protons or too many neutrons, one of the protons or neutrons is transformed into the other. 
• This is a particle and not a wave

Gamma Rays:

• Gamma decay is the emission of energy in the form of electromagnetic waves from the nucleus of the atom.
• Gamma Rays do not have rest mass just as any electromagnetic waves. 

Alpha Particles:

•  ( 2α 4 ) Alpha particles are particles with the number of protons (atomic number) 2 and the number of neutron and proton (mass number)  4. It is similar to Helium Atom.
• It is obtained from the radioactive decay process of a heavy nucleus. 
• It is particle and not a wave. 

Ultrasonic waves

• The ultrasonic waves are mechanical waves and do not lie in the category of electromagnetic waves.
• These are waves like sound waves having a frequency of more than 20,000 Hz. 
• These are not audible to normal human ears. 

Explanation:

The following things can be concluded.

• α and β rays are particles and not wave. 
• γ is an electromagnetic wave. 
• Ultrasonic waves are mechanical waves.

So, the only electromagnetic wave is γ. 

The correct answer is X-rays.

Concept:

• Electromagnetic spectrum: The complete range of light that exists in nature is called an electromagnetic spectrum.
• Light is an electromagnetic wave and the distance between two successive crests or two successive troughs of the light wave is called a wavelength of the light wave.
• The wavelength of light is denoted by λ.
• As shown in the spectrum, the wavelength increases when we go from left to right.

From the spectrum, we can see that the X rays has the maximum frequency and least wavelength as compared to UV, Microwave and Infrared rays. 

Electromagnetic (EM) spectrum: 

The electromagnetic (EM) spectrum is the range of all types of EM radiation arranged according to frequency or wavelength.

• In order of  decreasing wavelength or increasing frequency these are:
• radio waves radiation, microwave radiation, infrared, visible light, ultraviolet, X-rays, and gamma rays.
•  

Analysis

The correct order of electromagnetic spectrum with decreasing frequency is:

X–rays > Ultraviolet rays > Infrared rays > Microwaves > Radiowaves

Concept:

Dispersion of light:

• Dispersion of light is the phenomenon of splitting a beam of white light into its constituent colours on passing through a prism.
• The band of seven colours so obtained is called the (visible) spectrum.
• The basic reason behind the dispersion of white light into seven different colours is because all the seven rays of light of different colours travel at different speeds through the glass prism. 

•  
• The degree of refraction also can be said as the bending of each light ray depends upon their individual speed while passing through the prism. 
• All the different colours of light rays travel at different speeds in glass and so the angle of bending or angle of refraction of each light ray are different. 

Explanation:

• The refractive index varies with wavelength linearly because different wavelengths interfere to different extents with the atoms of the medium.

\(Bending\;\alpha \;\frac{1}{{Wavelength}}\)

• It is important to use monochromatic light to prevent dispersion of light into different colours.
• The chosen wavelength should not be absorbed by the medium.

So, dispersion of light takes place because of differences in refractive index for different wavelengths.

CONCEPT:

Electromagnetic waves or EM waves:

• The waves that are formed as a result of vibrations between an electric field and a magnetic field and they are perpendicular to each other and to the direction of the wave is called an electromagnetic wave.
• The accelerating charged particle produces an electromagnetic (EM) wave.
• A charged particle oscillating about an equilibrium position is an accelerating charged particle.
• Electromagnetic waves do not require any matter to propagate from one place to another as it consists of photons. They can move in a vacuum.

EXPLANATION:

The wavelength of different electromagnetic waves:

• From the above table, it is clear that the wavelength of microwaves is maximum among the gamma rays, x-rays, and ultraviolet rays. Hence, option 3 is correct.

CONCEPT:

• Light or visible light commonly refers to electromagnetic radiation that can be detected by the human eye.
  • The entire electromagnetic spectrum is extremely broad, ranging from low energy radio waves with wavelengths that are measured in meters to high energy gamma rays with wavelengths that are less than 1 × 10^-11 meters. 
• Visible light is usually defined as having wavelengths in the range of 400-700 nanometers (nm), or 4 × 10^-7 to 7 ×  10^-7m between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths).
• This wavelength means a frequency range of roughly 430-750 terahertz(THz).

EXPLANATION:

• As we can see in the diagram that Red light has the longest wavelength.
• Hence option 2 is the answer.

Concept:

The waves which are produced by the motion of electrically charged particles are called as electromagnetic radiation. These waves have both electric as well as magnetic fields and is transverse in nature.

Electromagnetic spectrum: It is the arrangement of electromagnetic radiations according to their frequency or wavelength. The electromagnetic spectrum has a range of frequencies, wavelengths, and photon energies.
Typically, electromagnetic waves travel at the speed of light in a vacuum.
The electromagnetic spectrum is as follows:

Explanation:

The wavelength of the waves given in the question are:

AM radio waves - 10² m

Microwaves - 10^-2 m

Infrared radiations - 10^-4 m

X-rays - 10^-10 m

Hence, Option (1) is the correct answer.

CONCEPT:

• Electromagnetic spectrum: It is a collection of a range of different waves in sequential order from radio to gamma electromagnetic waves.

Frequency (ν) = speed of light (c)/wavelength (λ)

• Microwaves: They come in the range of 1 mm to 0.1 meters and of the frequency range between 300 MHz to 300 GHz.
  • Microwaves are generally used in Radars, Transmission towers, Microwave Ovens, etc.

EXPLANATION:

• The wavelength range of the microwave is 1 mm to 0.1 m.
• Hence option 1 is correct.

Additional Information

CONCEPT:

• Electromagnetic spectrum: The complete range of light that exists in nature is called an electromagnetic spectrum.
• The waves that are created as a result of vibrations between an electric field and a magnetic field is called Electromagnetic waves.
• The waves of the electromagnetic field, propagating through space and carrying electromagnetic radiant energy is called electromagnetic radiation.
• It consists of radio waves, microwaves, infrared, light, ultraviolet, X-rays, and gamma rays.

EXPLANATION:

• From the above, it is clear that alpha ray, also called alpha particles alpha ray, contains two protons and two neutrons bound together into a particle just like a helium-4 nucleus, and it not an electromagnetic rays.