Important Questions for Class 12 Chapter 8 - Electromagnetic Waves

Important questions based on NCERT syllabus for Chapter 8 - Electromagnetic Waves:

Question-1: 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?

E and B will be mutually perpendicular and perpendicular to direction of propagation in x-y plane.
Wavelength = c / f
= (3 x 108)/(30 x 10^6)
= 10 m.

Question-2: The amplitude of the magnetic field part of a harmonic electromagnetic wave in vacuum is B0 = 510 nT. What is the amplitude of the electric field part of the wave?

Given,Bo = 510 nT
Using the relation
⇒Eo / Bo = c
⇒Eo = c.Bo
⇒Eo = (3 × 108).(510 × 10^-9 )
⇒Eo = 153 N / C

Question-3: For X-rays of wavelength 10−10m, red light of wavelength6800 Å and radiowaves of wavelength 500 m, what physical quantity could be the same?

The speed of light (3×108 m/s) in a vacuum is the same for all wavelengths. It is independentof the wavelength in the vacuum.