Six original Cambridge-style questions. They cover what ultrasound is, its uses in sonar and scanning, why it is safe where X-rays are not, and distance calculations with the all-important factor of two.
State what is meant by ultrasound, and give the approximate frequency above which sound is classed as ultrasound.
State two practical uses of ultrasound.
Detecting flaws inside metal parts is also accepted.
A ship sends a pulse of ultrasound straight down and receives the echo from the seabed 0.50 s later. The speed of sound in seawater is 1500 m/s. Calculate the depth of the seabed.
Total path: v t = 1500 x 0.50 = 750 m
d = v t / 2 = 750 / 2d = 375 m
The pulse travels down and back, so the depth is half the total path.
During a medical scan, a pulse of ultrasound enters the body and reflects from a boundary between two tissues. The echo is received 0.000040 s (40 microseconds) after the pulse is sent. The speed of sound in the tissue is 1500 m/s. Calculate the depth of the boundary below the skin.
Total path: v t = 1500 x 0.000040 = 0.060 m
d = v t / 2 = 0.060 / 2d = 0.030 m (3.0 cm)
A sensible depth inside the body.
Ultrasound, rather than X-rays, is used to scan an unborn baby. Explain why ultrasound is the safer choice.
Explain how a pulse of ultrasound is used to measure the distance to a boundary inside the body, and explain why the distance is half of v times t.
Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.