# AQA Science © Nelson Thornes Ltd 2006 1 P3 2 Summary Light and sound Jim Reed/Digital Vision WW (NT)

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AQA Science © Nelson Thornes Ltd 2006 1 P3 2 Summary Light and sound Jim Reed/Digital Vision WW (NT)

P3 2 Summary AQA Science © Nelson Thornes Ltd 2006 2 How is light reflected from a surface? Angles of incidence, reflection and refraction are always measured between the ray and the normal. The normal at a point on a mirror is perpendicular to the mirror. For a light ray reflected by a mirror: the angle of incidence = the angle of reflection. Real images are formed where rays of light cross so they can be produced on a screen. Virtual images cannot be produced on a screen – they are where rays of light appear to have come from.

P3 2 Summary AQA Science © Nelson Thornes Ltd 2006 3 What happens with a curved mirror? The principal focus of a concave mirror is the point where parallel rays of light are focused to by the mirror. A concave mirror forms: –a real image if the object is beyond the principal focus, –a virtual image if the object is between the mirror and the principal focus. A convex mirror always forms a virtual image of an object. Photodisc 46 (NT)

P3 2 Summary AQA Science © Nelson Thornes Ltd 2006 4 What is refraction? Refraction of light is the change of direction of a light ray when it crosses a boundary between two transparent substances. If the speed is reduced, refraction is towards the normal (e.g. air to glass). If the speed is increased, reflection is away from the normal (e.g. glass to air). SPL: Alfred Pasieka

P3 2 Summary AQA Science © Nelson Thornes Ltd 2006 5 What are converging and diverging lenses? A converging lens makes parallel rays of light converge to a focus. The point where they are focused is the principal focus of the lens. A diverging lens makes parallel rays of light diverge (spread out). The point where the rays appear to come from is the principal focus of the lens. Corbis V257 (NT)

P3 2 Summary AQA Science © Nelson Thornes Ltd 2006 6 What type of images do the lenses form? A real image is formed by a converging lens if the object is between its principal focus and infinity. A virtual image is always formed by a diverging lens, and by a converging lens if the object is between the principal focus and the lens.

P3 2 Summary AQA Science © Nelson Thornes Ltd 2006 7 How is a converging lens used in a camera? A camera contains a converging lens that is used to form a real image of an object.

P3 2 Summary AQA Science © Nelson Thornes Ltd 2006 8 How is a converging lens used in a magnifying glass? A magnifying glass is a converging lens that is used to form a virtual image of an object. Photo: S. Meltzer/Photolink/Photodisc 24 (NT)

P3 2 Summary AQA Science © Nelson Thornes Ltd 2006 9 What is sound? Sound waves: are longitudinal waves. can travel through liquids and gases and in solids. cannot travel in a vacuum. can be reflected (echoes) and refracted.

P3 2 Summary AQA Science © Nelson Thornes Ltd 2006 10 How do we make musical sounds? We change the volume – the loudness of a note depends on the amplitude of the sound waves. We make the notes higher or lower – the pitch of the note depends on the frequency of the sound waves. Photo: Doug Menuez/Photodisc 45 (NT)

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