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O LevelPhysicsCambridgeExam Questions3. Waves3.2 Light

Light (Cambridge O Level Physics)

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3.2 Light

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3.2 Light

1a3 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.
screenshot-2022-11-08-at-11-42-32
(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]

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1b4 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 space equals space fraction numerator 0.5 b over denominator a end fraction.
  
  
n = ........................................................ [1]

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1c1 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 space equals space fraction numerator 0.71 b over denominator a end fraction.

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

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1d2 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.

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1e1 mark

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

  

square   Carry out the experiment in a darkened room.

square   Use pins that are taller than the height of the block.

square   View the bases of the pins.

square   View the pins with one eye closed.   

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2a1 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]

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2b3 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]

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2c2 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).
mirror[1]

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2d2 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:  

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2e1 mark

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

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31 mark

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

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

p3-1a

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.

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