CAIE IGCSE Physics 3.2.3 Thin Lenses Topic Practice

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Covered syllabus points

3.2.3.1—Action of thin converging and thin3.2.3.2—Terms focal length, principal axis and3.2.3.3—Ray diagrams for the formation of a3.2.3.4—Characteristics of an image using the3.2.3.5—A virtual image is formed when3.2.3.6—Ray diagrams for the formation of a3.2.3.7—Use of a single lens as a magnifying3.2.3.8—Use of converging and diverging lenses

Question 1

[Maximum number: 9]

Fig. 7.1 is a full-scale diagram of a small nail N in front of a thin converging lens. The line L represents the lens.

Fig. 7.1 (full scale)

Fig. 7.1 (full scale)

The focal length of the lens is 3.0 cm .

Question (a)

(a)

Rays of light, parallel to XY , are travelling towards the lens.

Describe what happens to the light after it passes through the lens.

[ 3 ]

Question (b)

(b)

On Fig. 7.1, mark and label with an F each of the two principal focuses of the lens.

[ 1 ]

Question (c)

(c)

The small nail N , of height 1.2 cm , is positioned 2.0 cm to the left of the lens.

[ 5 ]

Question (i)

(i)

By drawing on Fig. 7.1, find the position of the image I of N and add image I to the diagram.

[ 3 ]

Question (ii)

(ii)

State and explain whether I is a real or a virtual image.

[ 1 ]

Question (iii)

(iii)

State the name given to a lens when it is used in this way.

[ 1 ]

Question 2

[Maximum number: 6]

Fig. 6.1 shows a thin converging lens used to produce a magnified image of an object AB.

Fig. 6.1

Fig. 6.1

Question (a)

(a)

Explain the meaning of the terms principal focus and focal length.
principal focus
focal length

[ 2 ]

Question (b)

(b)

On Fig. 6.1, draw the magnified image of AB. Show your working.

[ 4 ]

Question 3

[Maximum number: 6]

Fig. 6.1 shows a full-scale diagram of an object O and its image I produced by a converging lens. The lens and its position on the principal axis are not shown.

Fig. 6.1

Fig. 6.1

Question (a)

(a)

On Fig. 6.1, draw:
- a single ray to locate the position of the centre of the converging lens
- a line to represent the position of the lens and label the line L.

[ 2 ]

Question (b)

(b)

Determine the focal length of the lens by drawing another ray on Fig. 6.1.

focal length =
[ 2 ]

Question (c)

(c)

The object is moved 2.0 cm closer to the lens.

State two changes to the characteristics of the image.
1
2

[ 2 ]
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