11.

A bucket full of hot water is kept in a room. It cools from 75°C to 70°C in t₁ minutes, from 70°C to 65°C in t₂ minutes and from 65°C to 60°C in t₃ minutes. Then

• t₁ < t₂ < t₃

• t₁ = t₂ = t₃

• t₁ < t₂ > t₃

• t₁ > t₂ > t₃

The equation of a transverse wave travelling along positive X-axis with amplitude 0.2 m, velocity 360 m/sec and wavelength 60 m can be written as

• $\mathrm{y} = 0.2 \sin \mathrm{\pi } \left[6\mathrm{t} + \frac{\mathrm{x}}{60}\right]$

• $\mathrm{y} = 0.2 \sin \mathrm{\pi } \left[6\mathrm{t} - \frac{\mathrm{x}}{60}\right]$

• $\mathrm{y} = 0.2 \sin 2\mathrm{\pi } \left[6\mathrm{t} - \frac{\mathrm{x}}{60}\right]$

• $\mathrm{y} = 0.2 \sin 2\mathrm{\pi } \left[6\mathrm{t} + \frac{\mathrm{x}}{60}\right]$

If v_m is the velocity of sound in moist air, v_d is the velocity of sound in dry air, under identical conditions of pressure and temperature.

• v_m < v_d

• v_m > v_d

• v_mv_d = 1

• v_m = v_d

If T is the reverberation time of an auditorium ofvolume V, then

• T ∝ V²

• T ∝ V

• $\mathrm{T} \propto \frac{1}{\mathrm{V}}$

• $\mathrm{T} \propto \frac{1}{{\mathrm{V}}^2}$

Two wires are fixed in a sonometer. Their tensions are in the ratio 8 : 1. The lengths are in the ratio 36 :35. The diameters are in the ratio 4 : 1. Densities of the materials are in the ratio 1 :2. If the higher frequency in the setting is 360 Hz, the beat frequency when the two wires are sounded together, is

• 8

• 5

• 10

• 6

A sound source is moving towards stationary listener with $\frac{1}{10}$th of the speed of sound. The ratio of apparent to real frequency is

• ${\left(\frac{9}{10}\right)}^2$

• $\frac{10}{9}$

• $\frac{11}{10}$

• ${\left(\frac{11}{10}\right)}^2$

If v is the speed of sound in air, then the shortest length of the closed pipe which resonates to a frequency n, is

• $\frac{\mathrm{v}}{2\mathrm{n}}$

• $\frac{\mathrm{v}}{4\mathrm{n}}$

• $\frac{4\mathrm{n}}{\mathrm{v}}$

• $\frac{2\mathrm{n}}{\mathrm{v}}$

Cavitation is a special application property exhibited only by

• ultrasonics

• electromagnetic waves

• audible sound

• infrasonics

Waves that cannot be polarised are

• electromagnetic waves

• light waves

• longitudinal waves

• transverse waves

A charge q is placed at the centre of the line joining two equal point charges each equal to Q. The system of 3 charges will be in equilibrium if q is equal to

• $+ \frac{\mathrm{Q}}{4}$

• $- \frac{\mathrm{Q}}{2}$

• $+ \frac{\mathrm{Q}}{2}$

• $- \frac{\mathrm{Q}}{4}$