Question 71
HAn ultrasound scanner is used to measure the width of a baby's head before birth.
The probe of the scanner sends pulses of ultrasound into the mother's body and detects the echoes.
The Figure shows the echoes from the front and the back of the baby's head.
The speed of ultrasound in the body is 1500 m/s.
Figure
a.[1]
Use the Figure to determine the time between the two echoes from the head.
b.[4]
Calculate the width of the baby's head in cm\text{cm}cm.
c.[2]
A gel is spread on the skin before the probe is placed on it.
Explain why.
d.[2]
Explain why ultrasound, rather than X-rays, is used to scan a baby before birth.