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?

Answer:

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?

Answer

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?

Answer

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?

Answer

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

Answer

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: