IGCSEPhysicsCambridge (CIE)Exam Questions3. WavesLight

Light (Cambridge (CIE) IGCSE Physics): Exam Questions

Exam code: 0625 & 0972

5 hours70 questions

Guided practice

3 marks

Some students determine the focal length of a converging lens by two different methods. They use the apparatus shown in Fig. 2.1.

Apparatus on a bench: a lamp behind a card with an illuminated triangle on the left, a converging lens in a holder in the middle and a screen on the right. Distance u is marked from the illuminated triangle to the lens and distance v from the lens to the screen.

A student sets the distance U between the illuminated triangle and the lens.

She moves the screen until a sharp image of the triangle is seen on the screen.

Method 1

On Fig. 2.1, the distance u between the illuminated triangle and the lens is $5.0 cm$ .

On Fig. 2.1, the distance v between the lens and the screen is $7.5 cm$ .

Fig. 2.1 is drawn to 1/5 scale.

(i) Calculate the actual distance U between the illuminated triangle and the lens, and the actual distance V between the lens and the screen, in the experiment.

U = ...............................................................

V = ...............................................................

[1]

(ii) Calculate a value $f_{1}$ for the focal length of the lens, using the equation:

$f_{1} = \frac{U V}{(U + V)}$

$f_{1}$ = .........................................................

[1]

(iii) Briefly describe a technique to obtain an image on the screen that is as sharp as possible in this experiment.

[1]

How did you do?

2 marks

Method 2

On Fig. 2.2, the height $h_{O}$ of the illuminated triangle is measured to be $1.5 cm$ .

On Fig. 2.3, the height $h_{I}$ of the image on the screen is measured to be $2.4 cm$ .

Fig. 2.2 shows the illuminated triangle, pointing upwards, with its height marked by a vertical double-headed arrow. Fig. 2.3 shows the larger, inverted image of the triangle on the screen, with its height marked by a vertical double-headed arrow.

(i) Calculate a value for the magnification M, using the equation:

$M = \frac{h_{I}}{h_{O}}$

M = .........................................................

[1]

(ii) Calculate a second value $f_{2}$ for the focal length of the lens, using the value of V from (a)(i) and the equation:

$f_{2} = \frac{V}{(M + 1)}$

$f_{2}$ = .........................................................

[1]

How did you do?

1 mark

State one precaution that could be taken to ensure that the measurements in the experiment are taken as reliably as possible.

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3 marks

A student is determining the refractive index n of the material of a transparent block.

Fig. 3.1 shows the outline ABCD of the transparent block.

(i) On Fig. 3.1:

draw a normal NL at the centre of side AB
- continue the normal so that it passes through side CD of the block
- label the point F where NL crosses AB
- label the point G where NL crosses CD.

[1]

(ii) Draw a line EF at an angle i = 30° to the left of the normal and above side AB.

[1]

(iii) Mark the positions of two pins P₁ and P₂ on line EF placed at a suitable distance apart for this type of ray-tracing experiment.

[1]

How did you do?

4 marks

The student observes the images of P₁ and P₂ through side CD of the block so that the images of P₁ and P₂ appear one behind the other.

He places two pins P₃ and P₄ between his eye and the block so that P₃, P₄ and the images of P₁ and P₂ seen through the block, appear one behind the other.

The positions of P₃ and P₄ are marked on Fig. 3.1.

(i) Draw a line joining the positions of P₃ and P₄. Continue the line until it meets the normal NL.

Label the point H where the line meets side CD. Draw the line FH.

[1]

(ii) Measure and record the length a of the line GH.

a = ........................................................ [1]

(iii) Measure and record the length b of the line FH.

b = ........................................................ [1]

(iv) Calculate the refractive index n using the following equation:

$n = \frac{0.5 b}{a}$ .

n = ........................................................ [1]

How did you do?

1 mark

Extended tier only

The student repeats the procedure using the angle of incidence i = 45°.

a = 3.2 cm

b = 6.9 cm

Calculate the refractive index n, using the equation $n = \frac{0.71 b}{a}$ .

n = ........................................................

How did you do?

2 marks

The student expected the two values of refractive index n obtained in this experiment to be equal.

State two difficulties with this type of experiment that could explain any difference in the two values of n.

How did you do?

1 mark

A student suggests precautions to take in this experiment to obtain reliable results. Tick one box to indicate the most sensible suggestion.

$□$ Carry out the experiment in a darkened room.

$□$ Use pins that are taller than the height of the block.

$□$ View the bases of the pins.

$□$ View the pins with one eye closed.

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1 mark

A student investigates the position of the image in a plane mirror.

Fig. 3.1 shows the ray-trace sheet he uses.

The student draws the line MR.

• He draws a normal NL to this line that passes through the centre of MR.

• He labels the point at which NL crosses MR with the letter B.

• He draws a line from B at an angle of incidence i = 30° to the normal below MR and to the left of the normal. He labels the end of this line A.

• He places a pin P₁ on line AB, as shown in Fig. 3.1. He places another pin P₂ on the line AB.

• He places the reflecting face of the mirror vertically on the line MR.

• He views the images of pins P₁ and P₂ from the direction indicated by the eye in Fig. 3.1.

(i) On Fig. 3.1, mark with a cross a suitable position for pin P₂ in this experiment.

[1]

(ii) He places two pins P₃ and P₄ some distance apart so that pin P₃ and the images of P₂ and P₁ all appear exactly behind pin P₄. The positions of P₃ and P₄ are shown on Fig. 3.1.

Draw the line joining the positions of P₃ and P₄. Continue the line until it extends at least 7.0 cm beyond MR.

[2]

How did you do?

3 marks

The student keeps pin P₁ in the same position but moves pin P₂ so that the angle of incidence i = 40°.

The pin positions P₅ and P₆ for the reflected ray are marked on Fig. 3.1.

(i) Draw the line joining the positions of P₅ and P₆. Continue the line until it extends at least 7.0 cm beyond MR.

Label with the letter Y the point where the two lines cross beyond MR.

[1]

(ii) Draw a line from P₁ to MR that meets MR at a right angle. Measure and record the length a of this line.

a = ..................................................... [1]

(iii) Draw a line from the point labelled Y to MR that meets MR at a right angle. Measure and record the length b of this line.

b = ..................................................... [1]

How did you do?

2 marks

The student removes all the pins. He places pin P₇ on the normal at a distance 6.0 cm from the front of the mirror.

He views the image of P₇ in the mirror.
He places pin P₈ on the normal behind the mirror.
He adjusts the position of P₈ so that the image of the bottom of the pin P₇ and the top of pin P₈ seen over the mirror appear as one pin when viewed from all angles in front of the mirror.

(i) On Fig. 3.1, measure the distance x along the normal between P₈ and the mirror.

x = ..................................................... [1]

(ii) Complete the diagram in Fig. 3.2 to show the appearance of the image of pin P₇ and pin P₈ as described in (c).

[1]

How did you do?

2 marks

The student expects the readings to show that the image formed in a plane mirror is the same distance behind the mirror as the object is in front of the mirror. Readings of a = b and x = 6.0 cm will show this.

State whether your readings show that the image formed in a plane mirror is the same distance behind the mirror as the object is in front of the mirror. Justify your statement by reference to the readings.

statement:

justification:

How did you do?

1 mark

A student carefully carries out an investigation into an image showing the position of different pins in a plane mirror.

Suggest a practical reason why the results may not be accurate.

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1 mark

A student is investigating the reflection of light by a plane mirror.

Fig. 1.1 shows his ray-trace sheet at full size.

The student carries out an initial experiment. He draws lines AB and CD as shown in Fig. 1.1. He then draws a line EF through a point N as shown in Fig. 1.1 and at an angle θ to line AB.

The angle θ is

measured to be 23° ±1°

Draw a normal to line AB at point N and extend the normal to line CD. Label the point at which the normal crosses line CD with the letter L.

How did you do?

2 marks

The student places a plane mirror on line EF and a screen with a 2 mm slit on line CD. He arranges the screen so that a ray of light shines along line LN. The ray reflected from the mirror passes through point P.

State and explain whether point P, shown on Fig. 1.1, is at a suitable distance from point N for this investigation.

How did you do?

2 marks

(i) Draw a line joining point N and point P. Extend this line until it meets line CD.

Label the point at which this line meets line CD with the letter G.

[1]

(ii) Measure the length a of line LG.

a = ................................................... cm [1]

How did you do?

4 marks

The student repeats the procedure for values of θ = 25°, 20°, 15°, 10° and 5°. His values for a are shown in Table 1.1.

Table 1.1

θ / °	a /cm
25	12.2
20	8.3
15	5.7
10	3.6
5	1.8

Use the values from Table 1.1 to plot a graph of a / cm (y-axis) against θ / ° (x-axis).

How did you do?

1 mark

Suggest a possible source of inaccuracy in this experiment, even if it is carried out carefully.

How did you do?

1 mark

A student wishes to check if his values for a are reliable.

Suggest how he could improve the experiment, using the same apparatus, to check the reliability of his results.

How did you do?

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D/cm	u/cm	v/cm	uv/cm²
70.0	22.0	48.4
75.0	20.7	54.5
80.0	20.0	60.0
85.0	19.5	65.8
90.0	19.0	71.2

$u / cm$	$h_{I} / cm$	$M$
20.0
30.0	1.5	0.93
40.0	0.9	1.6
50.0	0.6	2.3
60.0	0.5	2.8