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Higher-o-O-o-

Past Paper questions

1991 - 2001

-o-O-o-

3.2 Refraction

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1991 Q36

Monochromatic light has a wavelength 600 nm and a speed of 3x108 ms-1 in air.

This light enters a liquid where its wavelength is 400 nm.

(a) Show that the refractive index of the liquid is 1.5.

(b) Calculate the value of the critical angle for the light in this liquid.

1997 Q36A beam of monochromatic light of frequency 4.85x1014 Hz passes from air into liquid paraffin.

In liquid paraffin the light has a speed of 2.10x108 ms-1.

(a) Calculate the refractive index of the liquid paraffin.

(b) What is the frequency of the light when it is in the liquid paraffin?

1991 Q9

The diagram below shows part of an optical fibre.

The core of glass fibre is covered in a glass skin which has a refractive index lower than that of the core.

(a) Why does the glass skin have a lower refractive index than the core?(b) To find the refractive index of the core, the following measurements were made using a narrow

beam of laser light of wavelength 633 nm.

x = 20

y = 13

What is the refractive index of the fibre core for this wavelength?

(c) Angle x is now gradually increased.

(i) What happens to angle y?

(ii) What effect does this have on angle

?(iii) Explain why there is a value for angle x above which the fibre core becomes less efficient in

transmitting light through it.

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1992 Q10

A pupil finds a glass prism of the shape shown below when she dismantles an old optical instrument.

To investigate the optical properties of the prism, she directs a narrow beam of red light towards the

prism as shown.

The glass prism has a refractive index of 1.52 for this red light.

(a) (i) Calculate the value of the critical angle for this light in the glass prism.(ii) On the square-ruled paper provided, draw the prism with the dimensions stated in the diagram.

On your diagram, show the passage of the light beam until after it emerges from the prism.

Mark on your diagram the values of all relevant angles.

(iii) A second beam of light, parallel to the first and of the same wavelength, is now directed onto

the prism at A.

Add to your diagram the complete path of this beam through the prism.

(b) How would a distant object appear when viewed through the prism when it is held as shown

below?

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1994 Q9

(a) The diagram below shows the path of a monochromatic beam of light through a triangular plastic

prism.

(i) Calculate the refractive index of the plastic.

(ii) Sketch a copy of the above diagram with ray PQRS clearly labelled.

(Sizes of angles need not be shown.)

Add to your drawing the path which the ray PQ would take from Q if the prism were made

of a plastic with a slightlyhigher refractive index.

(b) The original prism is now replaced with one of the same size and shape but made from glass of

refractive index 1.80.

(i) Calculate the critical angle for this glass.

(ii) Draw an accurate diagram, showing the passage of the ray PQ through this prism until after it

emerges into the air.

Mark on your diagram the values of all relevant angles.

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1995 Q9

A swimming pool is illuminated by a lamp built into the bottom of the pool.

Three rays of light from the same point in the lamp are incident on the water-air boundary with

angles of incidence of 30, 40 and 50, as shown above.

The refractive index of the water in the pool is 1.33.

(a) Draw a diagram to show clearly what happens to each ray at the boundary.

Indicate on your diagram the sizes of appropriate angles.

Allnecessarycalculationsmustbeshown.

(b) An observer stands at the side of the pool and looks into the water.

Explain, with the aid of a diagram, why the image of the lamp appears to be at a shallower depth

than the bottom of the pool.

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1998 Q10

(a) The following diagram shows a ray of monochromatic light passing from air into a block of

borate glass.

The diagram is drawn to scale.

(i) Use measurements taken from the above diagram to calculate the refractive index of borateglass for this light. You will need to use a protractor.

(ii) Calculate the value of the critical angle for this light in the borate glass.

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(b) The following graph shows how refractive index depends on the type of material and the

wavelength in air of the light used.

A ray of light of wavelength 510 nm in air passes into a block of quartz.

(i) Calculate the wavelength of this light in the quartz.

(ii) Explain what happens to the value of the critical angle in quartz as the wavelength of visible

light increases.

(iii) A ray of white light enters a triangular prism made of crown glass, producing a visible

spectrum on a screen, as shown below.

The crown glass prism is now replaced by a similar prism made from flint glass.

Describe how the visible spectrum on the screen will be different from before.

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1999 Q9

A laser beam is used to investigate the refraction of light from water into air.

A waterproof laser is placed within a tank of water and the laser beam is directed towards the water

surface as shown below.

(a) The water in the tank has a refractive index of 1.33.

Describe what will happen to the ray of light at the water surface.

You must justify your answer by calculation.

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(b) The water in the tank is replaced by another liquid.

The position of the laser is altered so that the laser beam follows the path shown in the diagram

below. The angle 1, and the angle 2, as shown in the diagram, are measured.

The measurements are repeated for different values of

1 and the corresponding values of

2.The values of sin 1 and sin 2 are used to plot the graph shown below.

Use information from the graph to calculate the refractive index of the liquid.

(c) Light from the laser has a wavelength of 670x10-9 m in air. What is the wavelength of the laser light

when passing through a liquid which has a refractive index of 1.47?

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2000 Q10

(a) The critical angle for light in a type of red plastic is 41.

Show that the refractive index of this red plastic is 1.52.

(b) This red plastic is used to make the rear reflector on a bicycle.

The diagrams below show the rear reflector on the bicycle and an enlarged view of the reflector.

Light from a car headlamp is reflected back to the car as shown in the diagram below.

(i) Explain why total internal reflection takes place at P.

(ii) Why is the intensity of the reflected light less than the intensity of the light incident on the

reflector?

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(c) (i) A ray of light from another car strikes the reflector from a different direction as shown below.

The refractive index of the red plastic is 1.52.

Calculate the values of angles a and b.

(ii) The light from a car headlamp strikes the rear of the bicycle and its reflector at an angle as

shown in the diagram below.

Give one reason why the intensity of the light reflected back to the car decreases as angle

increases.

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2001 Q9

A ray of white light is incident on a semicircular glass block as shown below.

A continuous spectrum is seen between points P and Q on the screen.

The refractive indices of the glass block are 1.51 for red light and 1.53 for violet light.

(a) Which point, P or Q, represents the violet end of the spectrum?

(b) Calculate the value of the angle between the ends of the spectrum.

(c) Which colour of light, red or violet, travels faster in the glass block?

You must Justify your answer.

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1997 Q9

(a) The diagram below shows the refraction of a ray of red light as it passes through a plastic prism.

Calculate the refractive index of the plastic for this red light.

(b) The refractive index of a glass block is found to be 1.44 when red light is used.

(i) What is the value of the critical angle for this red light in the glass?

(ii) The diagram shows the paths of two rays of this red light, PO and QO, in the glass block.

When rays PO and QO strike the glass-air boundary, three further rays of light are observed.

Copy and complete the diagram to show all fiverays.

Clearlyindicate which of the three rays came from P and which came from Q.

The values of all angles should be shown on the diagram.

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