Ultrasound and X-rays are both used in medical imaging.

1. (a)(i)Define what is meant by ultrasound. ............................................................................................................................................................................. [2][2]
2. (a)(ii)Describe what happens to ultrasound waves as they meet the boundary between two different materials. ............................................................................................................................................................................. [2][2]
3. (a)(iii)To produce the image of an unborn child, an ultrasound emitter and receiver are placed close together on the mother's skin. Fig. 9.1 shows pulses detected by the receiver. [Figure 9.1 (graph of pulse amplitude vs time, showing pulse A and pulse B)] Pulse A is the emitted pulse and pulse B is the first pulse that returns from the unborn child. The average speed of ultrasound in human tissue is 1500 m/s. Calculate the distance between the emitter and the child. distance = ..................................................... [3][3]
4. (a)(iv)The speed of ultrasound in human tissue is close to the speed of sound in water. Suggest approximate values for the speed of sound in gases and solids. speed in gases ........................................................................................................................................................ speed in solids ...................................................................................................................................................... [2][2]
5. (b)(i)Fig. 9.2 shows an X-ray image of a hand. An X-ray detector is placed just below the hand. An image of the bones and human tissue around the bones is formed on a screen by the detector. [Figure 9.2 (X-ray image of a hand, with 'screen' labelled)] Describe what happens to the X-rays to produce the image. ............................................................................................................................................................................. ............................................................................................................................................................................. ............................................................................................................................................................................. [3][3]
6. (b)(ii)The wavelength of the X-rays used is 2.0 × 10⁻⁹ m. The speed of electromagnetic waves is 3.0 × 10⁸ m/s. Calculate the frequency of the X-rays. frequency = ..................................................... [2][2]
7. (b)(iii)Suggest one reason why X-rays are not used to form an image of an unborn child. ............................................................................................................................................................................. [1][1]

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