21.

A point performs simple harmonic oscillation of period T and the equation of motion is given x = a sin (ωt + π/6). After the elapse of what fraction of the time period the velocity of the point will be equal to half of its maximum velocity? 

• T/8

• T/6

• T/3

• T/3

The wave described by y = 0.25 sin (10 π x -2 πt), where x and y are in metre and t in second, is a wave travelling along the 

• - ve x direction with frequency 1 Hz

• +ve x direction with frequency π  Hz and wavelength λ = 0.2 m

• +ve x direction with frequency 1 Hz and wavelength λ = 0.2 m

• +ve x direction with frequency 1 Hz and wavelength λ = 0.2 m

At 10^o C the value of the density of a fixed mass of an ideal gas divided by its pressure is x. At 110^o C this ratio is

• x

• 383x/283

• 10x/110

• 10x/110

The electric potential at a point in free space due to a charge Q coulomb is Q x 10¹¹ V. The electric field at that point is

The voltage gain of an amplifier with 9% negative feedback is 10. The voltage gain without feedback will be

• 90

• 10

• 1.25

• 1.25

The energy required to charge a parallel plate condenser of plate separation d and plate area of cross-section A such that the uniform electric field between the plates is E, is

A current  of 3 A flows through the 2 Ω resistor shown in the circuit. The power dissiated in the 5 Ω resistor is 

diagram

• 4 W

• 2 W

• 1 W

• 1 W

A particle mass m, charge Q and kinetic energy T enter a transverse uniform magnetic field of induction. After 3 s the kinetic energy of the particle will be

• 3T

• 2T

• T

• T

A wire of a certain material is stretched slowly by ten percent. Its new resistance and specific resistance become respectively

• 1.2 times, 1.1 times

• 1.21 times, same

• both remain the same

• both remain the same

In the phenomenon of electric discharge through gases at low pressure, the coloured glow in  the tube appears as a result of 

• excitation of electrons in the atoms

• a collision between the atoms of the gas

• a collision between the charged particle emitted from the cathode and the atoms of the gas

• a collision between the charged particle emitted from the cathode and the atoms of the gas