GRADE 9 PHYSICS WORKSHEET - LIGHT
1. Fig. 10.2 shows a small object P in front of a plane mirror M. On Fig. 10.2, carefully draw two rays that show how
the mirror forms the image of object P. Label the image I. [3]
2. (a) Explain what is meant by
(i) total internal reflec on,
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(ii) cri cal angle. ...........................................................................................................................................
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(b) Fig. 7.1 shows a ray of light, travelling in air, incident on a glass prism.
(i) The speed of light in air is 3.0 × 10^8 m / s. Its speed in the glass is 2.0 × 10^8 m / s. Calculate the refrac ve
index of the glass.
refrac ve index = ...........................................................[2]
(ii) Show that the cri cal angle for the glass-air boundary is 42°. [1]
(iii) On Fig. 7.1, draw carefully, without calcula on, the con nua on of the ray through the prism and into the air.
[3]
3. The refrac ve index n of glass in air is 1.5.
(a) (i) State the equa on that relates the speed of light in air va, the speed of light in glass vg and n.
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The speed of light in air is 3.0 × 10^8 m / s. Calculate the speed of light in glass.
speed = .........................................................[1]
(b) Light travelling in glass strikes the edge of the glass. Fig. 6.1 shows a ray of light at an angle of 41° to the normal.
(i) The light passes from the glass into the air. Calculate the angle that the ray makes with the normal in the air.
angle = .........................................................[2]
(ii) State what happens to light that strikes the edge of the glass at an angle to the normal much larger than 41°.
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(c) Describe one example of how op cal fibres are used in medicine.
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4. Fig. 7.1 shows the principal axis PQ of a converging lens and the centre line XY of the lens.
An object 2.0 cm high is placed 2.0 cm to the le of the lens. The converging lens has a focal length of 3.0 cm.
(a) On Fig. above, draw a full-scale diagram to find the distance of the image from the lens, and the height of the
image.
distance of image from the lens = ......................................................
height of image = ...................................................... [5]
(b) State and explain whether the image in (a) is real or virtual.
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5. (a) Fig. 7.1 shows a ray diagram of a converging lens forming the image I of the object O.
(i) Put a ck in two boxes in the following list to describe the image formed by the lens in Fig. 7.1.
(ii) Which length, on Fig. 7.1, is the focal length of the lens? Circle one of the lengths below. [3]
6. Fig. 6.1 shows an object, the p of which is labelled O, placed near a lens L. The two principal foci of the lens are
F1 and F2.
(a) On Fig. 6.1, draw the paths of two rays from the p of the object so that they pass through the lens and
con nue beyond.
Complete the diagram to locate the image of the p of the object. Draw in the whole image and label it I. [3]
(b) Describe image I
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7. Fig. 6.1 shows wavefronts of light crossing the edge of a glass block from air into glass
(a) On Fig. 6.1
(i) at edge of glass draw in an incident ray, a normal and a refracted ray that meet at the same point on the edge of
the glass block
(ii) label the angle of incidence and the angle of refrac on,
(iii) measure the two angles and record their values.
angle of incidence = ..................................
angle of refrac on = .................................. [4]
(b) Calculate the refrac ve index of the glass.
refrac ve index = ..................................[3]
8. (a) The refrac ve index of a type of glass is 1.6. Calculate the cri cal angle for light in this type of glass.
cri cal angle = ...........................................................[3]
(b)A waterproof laser is immersed in water. Fig. 7.1 shows the laser shining light up towards the horizontal
surface of the water.
Ini ally, the angle θ is much less than the cri cal angle for this light in water. The laser moves and θ gradually
increases un l it is much greater than the cri cal angle. Describe, for different angles of the laser, what happens
to the light beam a er it hits the surface.
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