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1. State the law of reflection. (lesson 29a)
2. An object is placed 20cm in front of a plane mirror. Where does the image appear to be? (29a)
3. A light ray enters a glass block and is refracted. Is it bent towards or away from the normal line? (29a)
4. Name 2 types of lens, and say what they do. (29a)
5. Explain how how you can see the writing on a piece of paper. (29b)
6. A camera and the eye both use a lens to focus an image. How are they a) similar, b) different? (29b)
7. Name the colours of the spectrum. (29c)
8. What colours are absorbed by a red filter? (29c)
9. Why does a red shirt appear red? (29c)
10. What colour would a red shirt appear in blue light? (29c)
11. Explain how you can hear a dog barking - starting with how the sound is produced by the dog. (29d)
12. Why can't sound sound travel through a vacuum? (29d)
13. How does hte loudness of a sound depend on the amplitude of the wave? (29d)
14. How doe the pitch of a sound depend on the frequency of the vibration? (29d)
15. Why do you see a lightning flash before you hear the thunder? (29e)

ANSWERS

1. The angle of reflection is always equal to the angle of incidence.
2. 20cm behind the mirror.
3. When light enters glass it is bent towards the normal line.
4. Convex and concave. Convex converges the rays, concave diverges the rays.
5. Light rays are reflected from the page into the eye. The rays are focussed to an image on the retina and the signals are sent to the brain along the optic nerve.
6. Both lenses are convex. In the eye the lens changes shape, in a camera the lens to a different position to focus the image.
7. Red, orange, yellow, green, blue, indigo, violet. (ROY G BIV)
8. Orange, yellow, green, blue, indigo and violet are absorbed. Only red passes through.
9. It reflects red light and absorbs all other colours.
10. Black.
11. The dogs vocal cords are vibrating, sending a wave through the air. The air molecules vibrate. The energy is transferred from molecule to molecule. Some of the energy is transferred to the ear-drum causing it to vibrate., the signal is then passed to the brain.
12. There are no molecules to vibrate, so no energy is transferred.
13. The bigger the amplitude the louder the sound.
14. The higher the frequency, the higher the pitch.
15. Light travels faster than sound.