Light (CIE IGCSE Physics)

Topic Questions

	Download	View
Medium

1a3 marks

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

p1-2a

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

The distance u between the illuminated triangle and the lens is 5.0 cm

The distance v between the lens and the screen is 7.5 cm

(i)

Fig. 2.1 is drawn to 1/5^th scale.

Calculate the actual distance U between the illuminated triangle and the lens in the experiment.

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

Calculate the actual distance V between the lens and the screen in the experiment.

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

[1]

(ii)

Calculate a value

f_{1}

for the focal length of the lens, using the following 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?

1b2 marks

On Fig. 2.2, the height of the illuminated triangle, h_O is measured to be 1.5 cm.

On Fig. 2.3, the height of the image, h_I, on the screen is measured to be 2.4 cm.

p1-2b

(i)

Calculate a value for the magnification M, using the following 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)(ii) and the equation:

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

$f_{2}$ = ......................................................... [1]

How did you do?

1c1 mark

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

How did you do?

1d1 mark

Suggest which of Method 1 or Method 2 is likely to give the more accurate value for the focal length.

Explain the reason for your choice.

How did you do?

Did this page help you?

2a3 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?

2b4 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?

2c1 mark

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?

2d2 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?

2e1 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.

How did you do?

Did this page help you?

3a1 mark

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

ray-diagram
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?

3b3 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?

3c2 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?

3d2 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?

3e1 mark

The student carries out this experiment with care. Suggest a practical reason why the results may not be accurate.

How did you do?

Did this page help you?

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