CAIE IGCSE Physics 3.2.2 Refraction of Light

Covered syllabus points

3.2.2.1—Terms normal, angle of incidence and 3.2.2.2—An experiment to show refraction of 3.2.2.3—Passage of light through a transparent 3.2.2.4—Meaning of critical angle 3.2.2.5—Internal reflection and total internal 3.2.2.6—Refractive index, n, as the ratio of 3.2.2.7—Refractive index: n = sin i / sin r 3.2.2.8—Critical angle relation: n = 1 / sin c 3.2.2.9—Use of optical fibres, particularly in

[Maximum number: 6]

Fig. 7.1 shows a container of oil.

Fig. 7.1

A ray of light shines on the surface of the oil. The refractive index of the oil is 1.47 .

(a)

On Fig. 7.1, draw the normal at the point where the ray enters the oil.

[ 1 ]

(b)

The angle x is $56^{\circ}$ .

Calculate the value of the angle of refraction.
angle of refraction =

[ 3 ]

$22^{\circ}$ $i=34\left({ }^{\circ}\right)$ $n=\sin i / \sin r \mathbf{O R}(r=) \sin ^{-1}\{\sin i / n\} \mathbf{O R} \sin r=\sin 34 / 1.47 \mathbf{O R} \sin r=0.38$

(c)

Calculate the speed of light in the oil.

Give your answer to three significant figures.

speed =

[ 2 ]

$2.04 \times 10^{8} \mathrm{~m} / \mathrm{s}$
n= speed of light in air / speed of light in oil

OR (speed of light in oil =) speed of light in air/n

OR (speed of light in oil = ) $3.0 \times 10^{8} / 1.47$

[Maximum number: 8]

Fig. 5.1 shows a ray of yellow light incident on a glass prism ABC .

Fig. 5.1

(a)

Explain why the ray does not change direction when it enters the prism at face AB.

[ 1 ]

ray travels along the normal OR angle of incidence $=0\left({ }^{\circ}\right)$

(b)

The critical angle for the glass is $42^{\circ}$ .

[ 5 ]

(i)

Calculate the refractive index of the glass.

Show your working.

refractive index =

[ 2 ]

$n=1 / \sin c \mathbf{O R}(n=) 1 / \sin c \mathbf{O R}(n=) 1 / \sin 42\left({ }^{\circ}\right)$
1.5

(ii)

On Fig. 5.1, continue the path of the light through the prism and after it leaves the prism.

[ 3 ]

ray reflected at BC AND no refracted ray
ray hits AC with angle of incidence $=0^{\circ}$
correct refraction of candidate's ray into air at AC

(c)

Internet data can be transferred using infrared waves in optical fibres.

State two advantages of using optical fibres to transmit data.
1

2

[ 2 ]

[Maximum number: 7]

Fig. 5.1 shows a block ABCD made of glass that has a refractive index of 1.5. The block has one curved side AB and three straight sides, BC, CD and DA.

Fig. 5.1

There are right angles at C and D. The curved side AB is one quarter of the circumference of a circle that has its centre at point P.

A ray of monochromatic light enters the block through the curved side AB and strikes side BC at P. Some light emerges into the air and some is reflected.

(a)

Explain why the ray of light does not change direction when it enters the block through side AB .

[ 2 ]

(b)

Show that the critical angle c for glass of refractive index 1.5 is $42^{\circ}$ .

[ 2 ]

(c)

Fig. 5.1 shows that the angle between the ray of light and line AP is $\theta$ , where line AP is at right angles to side BC.

Angle $\theta$ increases to $45^{\circ}$ .

[ 3 ]

(i)

State and explain what happens to the light that strikes P .

[ 2 ]

all light is reflected
$\theta$ / angle of incidence >c / critical angle

(ii)

When $\theta=45^{\circ}$ , the reflected light strikes side CD.

Describe what happens when this reflected light strikes side CD.
[Total: 8]

[ 1 ]

all light is reflected OR reflected ray at $90^{\circ}$ to incident ray OR reflected ray is parallel to original ray

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CAIE IGCSE Physics 3.2.2 Refraction of Light Topic Practice

Covered syllabus points

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