# Electromagnetic Waves NCERT Class 12 Physics Entrance Exams Questions & Answers

Physics XII (2nd. Year Science) UNIT-V ELECTROMAGNETIC WAVES electromagnetic waves produced by electromagnetic waves class 12 electromagnetic spectrum electromagnetic waves meaning types of electromagnetic waves electromagnetic waves properties electromagnetic waves mcq pdf electromagnetic waves conceptual questions electromagnetic waves previous year questions neet em waves previous year questions jee electromagnetic waves questions and answers pdf electromagnetic waves multiple choice questions and answers pdf

ELECTROMAGNETIC WAVES

1. Electromagnetic waves are produced by accelerated charge. (Discovered by J.C. Maxwell)
2. Electromagnetic waves are transverse in nature.
3. If E⁰ and B⁰ be the amplitudes of electric intensity
and magnetic induction respectively, then E⁰/B⁰=
C = Velocity of electromagnetic waves constant.
4. Velocity of electromagnetic waves is given by
C= 1/√μ°€°(In space)

4.(A) Velocity of electromagnetic wave in any medium
is given by
V= 1/√μ€

1. Velocity of electromagnetic waves does not depend on the frequency or wavelength or amplitude of the waves.
2. Electromagnetic waves do not require a material medium for their propagation.
3. For material medium the velocity of electromagnetic waves depend on the value of permeability and permittivity for that medium.
4. Electromagnetic waves are unaffected by electric and magnetic fields.
5. The energy in electromagnetic waves is divided equally between electric and magnetic vectors.
6. Average electric energy density Ué=1/2e⁰E⁰² and average magnetic energy density – Um=1/2 E⁰E⁰²
7. The optical effect of electromagnetic waves is only on account of electric vector. Hence electric vector is sometimes called as the light vector.
8. Electromagnetic waves have frequency range 10² to 10 Hz.
9. The wavelength varies between 1018m to about 10⁶ m.
10. (a) Electromagnetic waves carry both energy and momentum.
(b) The basic source of electromagnetic wave is an electric dipole.
(c) The oscillations of Eand B fields are in same phase.
V = few Hz to 10⁹ Hz
μ= A few Km to 0.3m.
It is used in radio and TV communication.
Its source is oscillating circuits i.e., LC circuit.
12. Medium waves (M.F)
v = 3 MHz to 0.6 MHZ o
n = 100 m to 500 m
few hundred kilometre only.
13. Short Waves
V 30 MHz to 3 MHz
A= 10 m to 100 m
14. Microwaves:
V = 10° Hz to 3x 10 Hz
Π= 0.3 m to 103 m
Its source is due to oscillating currents in special
vacuum tubes.
Used in radars, telemetry, microwave oven and
in the study of atomic and molecular structure.
15. Infra Red Spectrum:
V= 3x 10 Hz to 4x 10¹⁴ Hz
Π= 10m to 7.5 x 10–⁷m
Used in medical science, industry, night time photography and astronomy etc. Its source is due to excitation of atoms and molecules.
16. Visible Spectrum:
V = 4x 10¹⁴Hz to 8x 10¹⁴ Hz
Π= 7.5 x 10–⁷m to 3.75 x 10-7m
Its source is due to excitation of atomns.
The sensitivity of eye is maximum for Π= 5.6 x 10 m (yellow colour)
17. Ultraviolet Rays:
V = 8x 10¹⁴ Hz to 3 x 10¹⁷ Hz
Π= 3.75 x 10–¹² m to 10–⁹m
Used in medical application and sterilisation processes and also to study the molecular structure. Its source is due to excitation of atoms.
18. X-rays
V=3x 10–¹⁶ Hz to 5x 10¹⁹ Hz
μ= 10–⁸ m to 6x 1o¹² m or, 0.1A to 100Ă
Used in medical sciences to study the structure of crystals and arrangement of atoms and molecules. Its source is bombardment of high atomic number target by fast electrons.
19. Gamma Rays:
V = 3x 10¹⁸ Hz to 3 x 10²² Hz
Π = 10-¹⁰m to 10–¹⁴m
Used in medical science for cancer treatment to produce nuclear reactions. Its source is nuclear origin.