Time taken to hear the echo if distance between the listener and the obstacle d is given by :

1. t = d x V

2. t = 2d x V

3. t = $\dfrac{V}{2d}$

4. t = $\dfrac{2d}{V}$

To detect the obstacles in their path, bats produce:

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

Infrasonic sound waves have a frequency :

1. between 20 Hz to 10,000 Hz
2. below 20 Hz
3. above 20,000 Hz
4. between 20 Hz to 20,000 Hz

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