Charge needed within a unit sphere centred at the origin for producing a potenti

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Question
Charge needed within a unit sphere centred at the origin for producing a potential field,
Options
A. 12 p_c
B. 60 p_c
C. 120 p_c
D. 180 p_c

Correct Answer

120 p_c

Explanation

Charge needed within a unit sphere centred at the origin for producing a potential field, 12 pc 60 p

⟹ q = 120p coulomb, r = 1 meter.

Electromagnetic Field Theory problems

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1. In a 100 turn coil, if the flux through each turn is (t³ - 2t)mW_b, the magnitude of the induced emf in the coil at a time of 4 sec is
Options
A. 46 mV
B. 56 mV
C. 4.6 V
D. 5.6 V

4. Which of the following is true as regards photo emission?
Options
A. Velocity of emitted electrons is dependent on light intensity
B. Rate of photo emission is inversely proportional to light intensity
C. Maximum velocity of electron increases with decreasing wave length
D. Both holes and electrons are produced

5. The most commonly used semiconductor material is
Options
A. silicon
B. germanium
C. mixture of silicon and germanium
D. none of the above

6. A wave is propagated in a waveguide at frequency of 9 GHz and separation is 2 cm between walls Calculate group velocity for dominant mode.
Options
A. 1.8 x 10⁸ m/sec
B. 5 x 10⁸ m/sec
C. 3 x 10⁸ m/sec
D. 1.5 x 10⁸ m/sec

7. A hollow rectangular waveguide has dimensions a = 2b. Calculate the amount of attenuation, if the frequency is 3 GHz, and b = 1 cm.
Options
A. 49
B. 47.33
C. 50.33
D. 50

8. A plane electromagnetic wave travels in dielectric medium of relative permittivity 9. Relative to free space, the velocity of propagation in the dielectric is
Options
A. increased by a factor of 9
B. increased by a factor of 3
C. unchanged
D. reduced by a factor of 1/3

9. Find the noise factor for an antenna at 27�C with equivalent noise temperature 30�K
Options
A. 20
B. 100
C. 300
D. 1.1

10. Refractive index of glass is 1.5. Find the wavelength of a beam of light with a frequency of 10¹⁴ Hz in glass. Assume velocity of light is 3 x 10⁸ m/sec in vacuum.
Options
A. 4 ?m
B. 3 ?m
C. 2 ?m
D. 1 ?m

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