To detect the obstacles in their path, bats produce:

1. Infrasonic waves
2. Ultrasonic waves
3. Electromagnetic waves
4. Radio waves.

With respect to ultrasonic waves, which of the following statements is incorrect ?

1. they travel undeviated through a long distance
2. they have a speed greater than the speed of sound in a medium
3. they are not easily absorbed in a medium
4. they can be confined to a narrow beam

The diagram shown below depicts a displacement time graph of particle a wave travelling with speed 20 m/s.

The frequency of the wave is :

1. 50 Hz
2. 33.3 Hz
3. 100 Hz
4. 1000 Hz

Assertion (A): Sound waves can travel in vacuum, but light waves cannot.

Reason (R): Light is an electromagnetic wave, but sound is a mechanical wave .

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true and R is not the correct explanation of A.
3. assertion is false but reason is true.
4. assertion is true but reason is false.