# Form 3 Physics Refraction of Light Questions and Answers

Form 3 Physics Refraction of Light Questions and Answers. In this session we are going to work several questions on refraction of light. Answers are in video format. The questions are useful to those preparing for KCSE exams and also for revision.

Lessons (**25**) * SHARE*

- 1.
Light travels through glass of refractive index 1.5 with a speed V. calculate the value of V. (speed of light in air = 3.0 x #10^8# m/s).

2m 58s - 2.
A ray of light incident on the surface of a glass prism is observed to behave as represented in the diagram in Fig. 6
Explain this observation.

3m 23s - 3.
A small object lies at the bottom of a water pond at a depth of 1.2m. Given that the refractive index of water is 1.3, determine the apparent depth of the
object. (Give your answers to 1 decimal place).

3m 13s - 4.
Fig. 10 shows the apparent position of a fly in air as seen by a fish in water. Sketch on the same diagram, rays to show the actual position of the fly.

3m 14s - 5.
(a) A ray of white light is incident on one face of a triangular glass prism.
(i) Draw a ray diagram to illustrate the dispersion of white light by the prism, showing only the red ® and violet (V) rays.
(ii) On the same diagram drawn in
(i), mark and label the initial angle of incidence, i, and the angles of reflection on the first face for red #r_R# and for violet #r_V#.
(iii) Snell’s law for the

13m 43s - 6.
A microscope is focused on a horizontal surface. Arectangular glass block 30mm thick is placed on the mark. The microscope is
then adjusted 10mm upwards to bring the mark back to focus. Determine the refractive index of the glass.

3m 9s - 7.
Figure 13 shows a semicircular glass block placed on a bench. A ray of light is incident at point O as shown. The angle of incidence, i, is just greater
than the critical angle of glass.
A drop of water is now placed on the bench so as to make contact with the glass at point O. Sketch on the same figure the path followed by the ray after placing the drop of water.

3m 15s - 8.
Figure 14 shows a ray of light incident on a glass prism.
If the critical angle of the glass is #39^0#, sketch on the same diagram the path of the ray until it emerges from the prism.

3m 49s - 9.
Figure 3 shows two rays of A and B entering a semicircular glass block which has a critical angle of #42^0#.
The rays are incident at an air-glass boundary at point O.
Complete the path of the two rays from point O. label A’ and B’ the corresponding rays.

2m 49s - 10.
Figure 1 shows the path of array of yellow light through a glass prism. The speed of yellow light in the prism is 1.88 x #10^8# m/s.
(a) Determine the refractive index of the prism material for the light (speed of light in vacuum c = 3.0 x #10^8 ms^-1#).
(b) Show on the figure the critical angle, c, and determine its value.
(c) Given that r =# 21.2^0#, determine the angle #theta# .

11m 10s - 11.
One of the conditions for total internal reflection to occur is that angle of incidence must be greater than the critical angle of the medium. State the other
condition.

1m 2s - 12.
Figure 13 shows a coin placed in a large empty container. An observer looking into the container from the position shown is unable to see the coin.
Sketch two rays from a point on the coin to show how the observer is able to see the image of the icon after the container if filled with water.

5m 39s - 13.
Figure 13 shows rays of light AO, BO and CO incident on a glass-air interface. OA’, OB’ and OC’ are the
corresponding emergent rays. Study and answer questions 13 and 14.
Determine the critical angles of the glass material.

4m 33s - 14.
Determine the refractive of index of the glass material.

4m 45s - 15.
Figure 6 shows a ray of light incident on the face of a water prism.
Sketch the path of the ray as it passes through the prism. Critical angle for water is #49^0#.

4m 50s - 16.
(a) State two conditions necessary for total internal reflection to occur.
(b) Figure 9 shows a ray of light incident on the boundary between two media 1 and 2 at an angle .
Show that the refractive index for a ray of light travelling from medium 1 to medium 2 is given by: #\ _1n_2=1/sintheta#
(c) Figure 10 shows a ray of light incident on one face of a block of ice of refractive index 1.31 and to

10m 27s - 17.
Determine the speed of light in water given that the speed of light in air is 3.0 x #10^8 ms^-1# and the refractive index of water is 1.33.

3m 1s - 18.
(a) Figure 10 shows a ray of light incident on a triangular glass prism and white screen S placed after the prism.
(i) Complete the path of the ray through the prism to show how a spectrum is formed on the screen.
(ii) A thermometer with a blackened bulb is placed at various parts of the spectrum.
State with reason, the region where the thermometer indicates the highest reading.
(b) A pin is place

5m 18s - 19.
A water wave of wavelength 18mm is incident on a boundary of shallow water at right angles. If the wavelength in the shallow end is 14.4mm, determine
the refractive index of water for a wave moving from the deep to the shallow end.

2m 42s - 20.
Figure 7 shows two rays of light incident normally to face PQ of a glass prism, whose critical angle is #42^0#.
Complete the diagram to show the paths of the two rays as they pass through the prism.

4m 39s - 21.
Figure 5, shows an object O at the bottom of a beaker full of liquid. An observer above the beaker sees its image at point X inside a liquid.
Determine the refractive index of the liquid.

2m 57s - 22.
Figure 9 shows a crosssection of an optical fiber made of two types of glass A and B. the refractive index of B is lower than that of A.
A ray of light enters the optical fiber at P and emerges from Q.
(i) Sketch the path of the ray through the fiber.
(ii) State the reason why light travels through the fiber as in (i) above.

2m 33s - 23.
Figure 3 shows a ray of light passing into a glass prism ABC.
Sketch the path of the ray as it travels from face AC (critical angle for glass is #42^0#).

3m 18s - 24.
Draw a ray diagram to show how a ray of light may be totally internally reflected two times in an isosceles right-angled glass prism.
(Assume that the critical angle of glass is #42^0#).

5m 9s - 25.
A nail at the bottom of a beaker containing glycerin appears to be 6.8cm below the surface of glycerin.
Determine the height of the column of glycerin in the beaker. (Take the refractive index of glycerin as 1.47)

2m 50s

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