A pulse of frequency 100kHz is emitted from an ultrasound scanner, and is reflected from a fetus 10cm below the transmitter placed on the mother’s abdomen. The speed of sound within the mother’s body is 500m/s. How long does it take for the pulse to reach the receiver which is adjacent to the transmitter?

Answer:

14) B

Distance of transmitter from abdomen = 10 cm = 0.1 m
Time taken to reach the abdomen = Distance ÷ Time = 0.1 ÷ 500 = 0.0002 s

Since the receiver is adjacent to the transmitter, distance from the abdomen to receiver must also equal 0.1m

Therefore, the time taken for the pulse to travel from the abdomen to the receiver must be equal to 0.0002 s.

Total time = 0.0002 + 0.0002 = 0.0004 s

0.0004 s = 0.4 ms