 # Lenses for SQA National 5 Physics 1. Ray diagrams

A ray diagram shows the path that a light ray entering a lens follows to form the image. To draw a ray diagram, two steps must be followed. Firstly, a ray must be drawn from the object to the lens parallely to the principal axis, which when goes through the lens, must pass through the principal focus. Secondly, a second ray must be drawn from the object passing through the centre of the lens. A third additional ray can also be drawn into the ray diagram. The normal at the point which the ray enters the lens is the line perpendicular to the surface at that point. The angle of incidence is the angle between the incident ray and the normal, whereas the angle of refraction is the angle between the refracted ray and the normal. # 1

Draw a diagram for a light ray entering a concave lens, labelling the normal, the angle of incidence and the angle of refraction.

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Draw a diagram for a concave lens whose focal length is 1.5 cm for an object placed 4 cm from the lens with height of 2 cm.

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Describe the type of image which is produced by the convex lens given in the ray diagram.

The convex lens produces a magnified, inverted and real image. # 4

Explain the process of constructing a ray diagram.

Firstly, a ray must be drawn from the object to the lens parallely to the principal axis, which when goes through the lens, must pass through the principal focus. Secondly, a second ray must be drawn from the object passing through the centre of the lens. A third additional ray can also be drawn into the ray diagram. # 5

Draw a diagram for a convex lens whose focal length is 2 cm for an object placed at 3 cm from the lens with height of 1.5 cm.

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