Light (Cambridge (CIE) IGCSE Co-ordinated Sciences (Double Award): Physics): Exam Questions

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]

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]

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]

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:  

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

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.