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 ]

Question 4

[Maximum number: 3]

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 .

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

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

Question 5

[Maximum number: 2]

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

Fig. 6.1

Fig. 6.1

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

Question 6

[Maximum number: 1]

The lens in a magnifying glass is a converging lens.

Fig. 4.1 shows the lens of the magnifying glass, its two focal points, F1F_{1} and F2F_{2}, and its principal axis.

Fig. 4.1

Fig. 4.1

Underline two words in the list that describe the image produced in (a)(ii).
inverted
real
upright
virtual

Question 7

[Maximum number: 1]

A page of printed text is placed 18 cm from a converging lens of focal length 35 cm .
Fig. 6.1 is a scale diagram of the arrangement with each of the two principal focuses (focal points) of the lens labelled F .

Fig. 6.1

Fig. 6.1

Converging lenses can be used as magnifying glasses.

State whether the image produced when a lens is used as a magnifying glass is real or virtual. Explain why.

Question 8

[Maximum number: 4]

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

Fig. 6.1

Fig. 6.1

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

Question 9

[Maximum number: 1]

The lens in a magnifying glass is a converging lens.

Fig. 4.1 shows the lens of the magnifying glass, its two focal points, F1F_{1} and F2F_{2}, and its principal axis.

Fig. 4.1

Fig. 4.1

A student using the magnifying glass sees a magnified image of an object.

On Fig. 4.1, mark:
- a point X on the principal axis for a possible position of the object
- a point E for a possible position of the student's eye.

Question 10

[Maximum number: 3]

The lens in a magnifying glass is a converging lens.

Converging lenses are used in spectacles (glasses) to correct one problem with vision.

State the name of the problem and explain how a converging lens is used to correct it. You may draw a diagram.
name of problem:

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