Physics Questions & Answers - Free Online Practice

4,141.

A plane sound wave of frequency 85.5Hz and velocity 342ms^-1 is reflected from a vertical wall. At what distance from the wall does the wave have antinode?

View answer & explanation

Correct answer is C

If F = 85.5Hz, V = 342ms^-1,
Then wavelength = V/F = 342/85.5 = 4m

Then if wavelength = 4m
=> wavelength/2 = 4/2 = 2m = NN,
Thus NA = wavelength/4 = 4/4 = 1m.

4,142.

The thermometric substance of an absolute thermometer is

alcohol

mecury

helium

platinum

View answer & explanation

Correct answer is B

Mercury is the “liquid of choice” in thermometers because mercury changes density very linearly.

4,143.

The driving mirror of a car has a radius of curvature of 1m. A vehicle behind the car is 4m from the mirror. Find the image distance behind the mirror.

8/7

4/9

9/2

4/7

View answer & explanation

Correct answer is B

A driving mirror is always a convex mirror which is always of negative focal length and always forms a virtual image

Thus if r = 1m = 100cm
f = 1/2 = -50
∴ if U = 4cm = 400cm
f = -50cm

∴1/u + 1/v = 1/f
1/400 + 1/v = -1/50
∴ -1/v = 1/400 + 1/50
-1/v = (1 + 8)/400 = 9/400
∴ v = -400/9
v = 4/9

4,144.

The terrestrial telescope has one extra lens more than the astronomical telescope. The extra lens is for

improving the sharpness

creating an inverted image

magnification of the image

erection of the image

View answer & explanation

Correct answer is D

The extra lens in the terrestrial telescope mounted at the middle between the objective lens and the eye piece is to re-invert the image so that it is upright.

4,145.

A ray of light strikes a plane mirror at an angle of incidence of 35°. If the mirror is rotated through 10°, through what angle is the reflected ray rotated?

70°

45°

25°

20°

View answer & explanation

Correct answer is D

When ever a ray of light is incident on a plane mirror at an angle of incidence l, if the mirror is then rotated through an angle θ, then the reflected ray is rotated through an angle twice θ

So if θ = 35°, then the reflected ray is rotated through 2 x 10^o = 20°