201.

Assertion: When a beetle moves along the sand within a few tens of centimetres of a sand scorpion, the scorpion immediately turns towards the beetle and dashes towards it. 

Reason:  When a beetle disturbs the sand, it sends pulses along the sand's surface. One set of pulses is longitudinal while the other set is transverse.

• if both assertion and reason are true and the reason is the correct explanation of the assertion

• if both assertion and reason are true and the reason is not the correct explanation of the assertion

• if assertion and reason is false

• if both assertion and reason are false statements

Light propagates rectilinearly because of its

• frequency

• velocity

• Wavelength

• Wave nature

What is the path difference for destructive interference?

• nλ

• $\frac{\left(\mathrm{n} + 1\right) \mathrm{\lambda }}{2}$

• n ( λ + 1)

• $\frac{\left(2\mathrm{n} + 1\right) \mathrm{\lambda }}{2}$

A siren emitting sound of frequency 800 Hz is going away from a static listener with a speed of 30 m/s. Frequency of the sound to be heard by the listener is (Take velocity of sound as 300 m/s)

• 733.3 Hz

• 481.2 Hz

• 644.8 Hz

• 286.5 Hz

If equation of dound wave is   y = 0.0015 sin ( 62.8 x + 316 t ) then its wavelength will be

• 0.2 unit

• 0.3 unit

• 0.1 unit

• 2 unit

The graph between wave number  $\left(\overrightarrow{\mathrm{\nu }}\right)$  and angular frequency  ( ω ) is

Assertion: The flash of  lightening is seen before the sound of thunder is heard. 

Reason:  Speed of sound is greater than speed of light.

• If both the assertion and reason are true and reason is a correct explanation of the assertion.

• If both assertion and reason are true but assertion is not a correct explanation of the assertion.

• If the assertion is true but the reason is false.

• If both assertion and reason are false.

If fundamental frequency is 50 and next successive frequencies are 150 and 250 then it is

• a pipe closed at both end

• a pipe closed at one end

• an open pipe

• a stretched pipe

A source of frequency 240 Hz is moving towards an observer with a velocity of 20 m/s. The observer is now moving towards the source with a velocity of 20 m/s. Apparent frequency heard by observer, if velocity of sound is 340 m/s, is

• 268 Hz

• 270 Hz

• 360 Hz

• 240 Hz

Assertion: Soldiers are asked to break steps while crossing the bridge. 

Reason: The frequency of thick marching may be equal to the natural frequency of bridge and may lead to resonance which can break the bridge.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If assertion is false but reason is true.