For which one of the following input combinations, the given logic circuit gives the output Y = 1 ?

• A = 0, B = 0, C = 0

• A = 0, B = 1, C = 0

• A = 0 ,B = 1, C = 1

• A = 1 ,B = 1 ,C = 1

In a semiconductor, 2/3rd of the total current is carried by electrons and remaining 1/3rd by the holes. If at this temperature, the drift velocity of electrons is 3 times that of holes, the ratio of number density of electrons to that of holes is

• $\frac{3}{2}$

• $\frac{2}{3}$

• $\frac{5}{3}$

• $\frac{3}{3}$

In an p-n-p transistor, 10¹⁰ holes enter the emitter in 10^-6 s. If 29% of holes is lost in the base, then the current amplification factor is

• 49

• 19

• 29

• 39

The electrical conductivity of a semiconductor increases when electromagnetic radiation of wavelength shorter than 600 nm is incident on it. The energy band gap (in eV) for the semiconductor is

• 1.50

• 0.75

• 2.06

• 1.35

Identify the mismatched pair

• Noise  —  Unwanted signals

• Repeater  —  Communication satellite

• Attenuation  —  Srengthening of signal

• Demodulation  —  Retrieval of information 

Pick out the wrong statement.

• Analog signals provide a continuous set of values

• Digital signals represent values as discrete steps

• Analog signals utilise the binary system

• Digital signals can be processed by logic gates

A ground receiver receives a signal at 5 MHz, transmitted by a ground transmitter at a height of 320 m, which is 110 km away from it. Then it can communicate through (radius of the Earth, R = 6400 km)

• space waves

• ground waves

• sky waves

• both sky and ground waves

68.

The power radiated by a linear antenna of length l at wavelength λ is

• directly proportional to l

• inversely proportional to λ

• inversely proportional to λ²

• directly proportional to λ²

An aperture of size a is illuminated by a parallel beam of light of wavelength λ. The distance at which ray optics has a good approximation is

• $\frac{{\mathrm{a}}^2}{\mathrm{\lambda }}$

• $\frac{\mathrm{\lambda }}{{\mathrm{a}}^2}$

• $\frac{\mathrm{\lambda }}{\mathrm{a}}$

• $\frac{{\mathrm{\lambda }}^2}{\mathrm{a}}$

Two plane wavefronts of light, one incident on a thin convex lens and another on the refracting face of a thin prism. After refraction at them, the emerging wavefronts respectively become

• plane wavefront and plane wavefront

• plane wavefront and spherical wavefront

• spherical wavefront and plane wavefront

• spherical wavefront and spherical wavefront