81.

The apparent frequency of a note is 200 Hz, when a listener is moving wIth a velocity of 40 ms^-1 towards a stationary source. When he moves away from the same source with the same speed, the apparent frequency of the same note is 160 Hz. The velocity of sound in air in m/s is

• 340

• 330

• 360

• 320

Select the right option in the following

• Christian Huygens, a contemporary of Newton established the wave theory of light by assuming that light waves were transverse.

• Maxwell provided the theoretical evidence that light is transverse wave.

• Thomas Young experimentally proved the wave behaviour of light and Huygens assumption.

• All the statements given above, correctly answers the question "what is light ?''

If white light is used in the Newton's rings experiment, the colour observed in the reflected light is complementary to that observed in the transmitted light through the same point. This is due to

• 90° change of phase in one of the reflected waves

• 180° change of phase in one of the reflected waves

• 145° change of phase in one of the reflected waves

• 45° change of phase in one of the reflected waves

A tuning fork A produces 4 beats/s with another tuning fork B of frequency 320 Hz. On filing one of the prongs of A,4 beats/s are again heard when sounded with the same fork B. Then, the frequency of the fork A before filing is

• 328 Hz

• 316 Hz

• 324 Hz

• 320 Hz

When the length of the vibrating segment of a sonometer wire is increased by 1%, the percentage change in its frequency is

• $\frac{100}{101}$

• $\frac{99}{100}$

• 1

• 2

The loudness and pitch of a sound note depends on

• intensity and frequency

• frequency and number of harmonics

• intensity and velocity

• frequency and velocity

The maximum particle velocity in a wave motion is half the wave velocity. Then the amplitude of the wave is equal to

• $\frac{\mathrm{\lambda }}{4\mathrm{\pi }}$

• $\frac{2\mathrm{\lambda }}{\mathrm{\pi }}$

• $\frac{\mathrm{\lambda }}{2\mathrm{\pi }}$

• λ

The ratio of the velocity of sound in hydrogen $\left(\mathrm{\gamma } = \frac{7}{5}\right)$ to that in helium $\left(\mathrm{\gamma } = \frac{5}{3}\right)$ at the same temperature is

• $\sqrt{\frac{5}{42}}$

• $\sqrt{\frac{5}{21}}$

• $\frac{\sqrt{42}}{5}$

• $\frac{\sqrt{21}}{5}$

An engine moving towards a wall with a velocity 50 ms^-1 emits a note of 1.2 kHz. Speed of sound in air is 350 ms^-1. The frequency of the note after reflection from the wall as heard by the driver of the engine is

• 2.4 kHz

• 0.24 kHz

• 1.6 kHz

• 1.2 kHz

A glass tube is open at both the ends. A tuning fork of frequency f resonates with the air column inside the tube. Now the tube is placed vertically inside water so that half the length of the tube is filled with water. Now the air column inside the tube is in unison with another fork of frequency f'. Then

• f' = f

• f' = 4f

• f' = 2f

• $\mathrm{f}\text{'} = \frac{\mathrm{f}}{2}$