A dentist uses a small circular mirror to inspect a patient's back tooth. Fig. 1 shows the mirror held close to the tooth. The dentist wants the image to be...
Question 1 Report
A dentist uses a small circular mirror to inspect a patient's back tooth. Fig. 1 shows the mirror held close to the tooth. The dentist wants the image to be upright and larger than the actual object so that a crack in the enamel can be seen clearly. The mirror is part of a handle and has a polished curved surface.
(a) Name the type of curved mirror shown. [1]
(b) Explain why the tooth must be placed between the mirror and point F to obtain the required image. [2]
(c) Give one difference between the image and the tooth, apart from its size. [1]
The diagram shows a cyclist's helmet visor with an anti-glare coating. Light from a low sun reflects from the front and back surfaces of the thin coating. The coating is designed so that some reflected light waves cancel, reducing glare. This question considers the reflection of light, not the sound waves or the potential difference in the bicycle lamp circuit.
(a) Name the law that relates the angle of incidence to the angle of reflection at either surface. [1]
(b) Give one benefit of reducing reflected sunlight for the cyclist. [1]
(c) Describe the type of image that would be formed by a smooth flat visor surface. [1]
Answer Details
Dentist's mirror
- (a) It is a concave mirror. [1]
- (b) An object inside the focal length of a concave mirror forms a virtual image. [1] This virtual image is upright and magnified. [1] Therefore the tooth must be between the mirror and F.
- (c) Apart from size, the image is virtual, appears behind the mirror, or cannot be formed on a screen. [1]
Anti-glare visor
- (a) The law is: angle of incidence equals angle of reflection, the law of reflection. [1]
- (b) Reducing reflected sunlight gives reduced glare, improved visibility, or a safer view of the road. [1]
- (c) A smooth flat visor surface forms a virtual, upright, same-size image. [1]
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