1.1. Higher Tier Only

Figure 1 shows an ultrasonic transmitter and receiver being used to detect cracks in steel rails. The transmitted and reflected pulses are shown on an oscilloscope's screen below.

The oscilloscope time base measures 10 microseconds per division on the horizontal axis.

Figure 1

Explain why there are two reflected pulses for transmitter B on the right.

1.2. Higher Tier Only

The speed of the ultrasound wave in steel is 6000 m/s.

Calculate the thickness of the steel in metres.

1.3. Higher Tier Only

Calculate the depth of the crack as a percentage of the thickness of the steel.