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1. When light changes direction as it passes into a glass block, it is called r---------. (lesson 19a)
2. What do you call a lens that is thicker in the middle than at the edge? (19a)
3. A ------- lens makes light rays spread out (diverge). (19a)
4. Give 2 uses of total internal reflection. (19a)
5. Name the colours of the spectrum, in order. (19b)
6. Which colours are absorbed by a white object? (19b)
7. Why does an object appear red to us? (19b)
8. Which type of radiation ha the longest wavelength? (19c)
9. Which type of rays give you a sun-tan? (19c)
10. Which type of rays are given off by any warm or hot object? (19c)
11. When sound travels through air, the molecules -------. (19d)
12. Can sound travel through empty space, (a vacuum)? (19d)
13. If a loudspeaker has a frequency of 120 Hz, how often does it vibrate? (19d)
14. What is the loudness of sound measured in? (19e)
15. What can people who work in noisy jobs do to protect their hearing? (19e)

ANSWERS

1. Refraction.
2. Convex.
3. Concave.
4. Cat's eye reflectors, optical fibre.
5. Red, orange, yellow, green, blue, indigo, violet. (ROY G. BIV).
6. None are absorbed, they are all reflected.
7. It reflects red light, but absorbs the other colours in the spectrum.
8. Radio waves.
9. Ultra-violet (UV) rays.
10. Infra-red (IR) rays.
11. Vibrate.
12. No.
13. 120 times in every second.
14. Decibels (dB).
15. Wear ear protection.