Q. Explain how bats use ultrasound to catch prey.
Ans. The bats produce high pitched ultrasonic waves which are not heard by humans. The
ultrasonic waves on striking the insect send back an echo, which is heard by the bat. On
hearing the echo the bat homes on the insect and catches it.
Q. How is ultrasound used for cleaning?
Ans. The object to be cleaned is placed in a tank fitted with ultrasonic vibrator. The tank is filled
with water containing detergent. When the ultrasonic vibrator is switched on the detergent
particles rub against the object at a very-very high speed and hence clean it.
Q.Explain how defects in a metal block can be detected by using ultrasound.
Ans. The ultrasound waves are allowed to pass through metal block to which are fitted detectors
to detect the waves. If the metal block has a very small defect, such as an air bubble or a crack,
then the ultrasound waves are reflected from such spots. The reflected ultrasonic waves indicates that metal block is defective.
Q.9. How does the stethoscope help the doctors in listening to the sound of the patients heart beat?
Ans. In a stethoscope, the sound produced within the body of a patient is picked up by a sensitive diaphragm and then reaches the doctor's ear by multiple reflections.
Q.Write the full name of SONAR. How will you determine the depth of a sea using echo ranging?
Ans: The full name of SONAR is Sound Navigation and Ranging. Sonar is based on the principle
of reflection of sound wave. Powerful pulses of ultrasound are sent out at regular intervals from a transmitter mounted on a ship. When these pulses are intercepted by submerged objects, they get reflected. The reflected sound or echo is detected by an underwater receiver, which is also mounted on the ship.
If speed of ultrasound be v and t is the elapsed time between the transmission and the reception of the ultrasound signal, the depth of the submerged object underwater is h =( v × t)/2