Physics Class 12 NCERT Solutions: Chapter 8 Electromagnetic Waves Part 2 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Relation between Velocity Frequency and Wavelength

Q: 4. A plane electromagnetic wave travels in vacuum along z-direction. What can you say about the directions of its electric and magnetic field vectors? If the frequency of the wave is 30 MHz, what is its wavelength?


The electromagnetic wave travels in a vacuum along the z-direction. The electric field (E) and the magnetic field (H) are in the plane. They are mutually perpendicular. Frequency of the wave,

Speed of light in a vacuum, Wavelength of a wave is given as:

Q: 5. A radio can tune in to any station in the band. What is the corresponding wavelength band?


A radio can tune to minimum frequency,

Maximum frequency,

Speed of light,

Corresponding wavelength for can be calculated as:

Corresponding wavelength for can be calculated as:

Thus, the wavelength band of the radio is to .

Q: 6. A charged particle oscillates about its mean equilibrium position with a frequency of . What is the frequency of the electromagnetic waves produced by the oscillator?


The frequency of an electromagnetic wave produced by the oscillator is the same as that of a charged particle oscillating about its mean position i.e.. .

Q: 7. The amplitude of the magnetic field part of a harmonic electromagnetic wave in vacuum is . What is the amplitude of the electric field part of the wave?


Amplitude of magnetic field of an electromagnetic wave in a vacuum,

Speed of light in a vacuum,

Amplitude of electric field of the electromagnetic wave is given by the relation,

Therefore, the electric field part of the wave is .

Q: 8. Suppose that the electric field amplitude of an electromagnetic wave is and that its frequency is . (A) Determine, , and . (B) Find expressions for E and


Electric field amplitude,

Frequency of source,

Speed of light,

(A) Magnitude of magnetic field strength is given as:

Angular frequency of source is given as:

Propagation constant is given as:

Wavelength of wave is given as:

(B) Suppose the wave is propagating in the positive x direction. Then, the electric field vector will be in the positive y direction and the magnetic field vector will be in the positive direction. This is because all three vectors are mutually perpendicular.

Equation of electric field vector is given as:

And, magnetic field vector is given as: