Light (Cambridge International IGCSE Physics): Exam Questions

Extended

Fig. 1.1 shows a light ray passing though a block of ice.

(not to scale)

Determine the refractive index of ice.

refractive index = ....................................

Explain why the angle of refraction is smaller than the incident angle for the boundary from air to ice.

Extract:

sin(i) = sin(46°)

n = sin(i)/sin(r) n = sin(46°)/sin(35°) n = 1.25

State the correct value of angle $θ$ on Fig. 1.1.

angle $θ$ = ....................................

Complete Table 1.2 by drawing a tick to show which properties of light change during refraction.

Table 1.2

The spectrum of white light is made up of seven colours.

Fig. 7.1 shows a partially-completed spectrum. Two labels are missing.

(i) On Fig. 7.1, write the name of the missing colour in each blank space.

(ii) On Fig. 7.1, indicate the direction of increasing wavelength for the spectrum. Draw an arrow in the box below the spectrum of colours.

A ray of red light strikes one face of a triangular glass prism as shown in Fig. 7.2.

(i) On Fig. 7.2, draw the path of the ray as it travels through the glass prism and enters the air.

(ii) State the term used to describe what happens to the ray of red light as it enters and leaves the prism.

Fig. 5.1 represents an object positioned on the principal axis of a thin lens.

Each small square of the grid represents 0.5 cm. Each principal focus of the lens is labelled F.

Use the grid to determine the focal length of the lens.

focal length = ..................................................... cm

Extract:

Fig. 5.1 represents an object positioned on the principal axis of a thin lens. Each small square of the grid represents 0.5 cm. Each principal focus of the lens is labelled F.

(i) On Fig. 5.1, draw a ray from the top of the object that passes through a principal focus, then through the lens and beyond it.

(ii) On Fig. 5.1, draw a second ray from the top of the object that passes through the centre of the lens. Continue the path of this ray to the edge of the grid.

(iii) On Fig. 5.1, draw an arrow to show the position and nature of the image produced by the lens.

An object, OX, is placed in front of a converging lens.

Fig. 7.1 shows a ray of light from the object passing through the lens.

(i) The lens forms an image of object OX.

On Fig. 7.1, draw another ray from X to locate the position of the image.

(ii) On Fig. 7.1, draw an arrow to represent the image of OX and label it I.

(iii) On Fig. 7.1, mark a principal focus for the lens and label it F.

(iv) On Fig. 7.1, measure and record the focal length of the lens.

focal length = ...................................................... cm [1]

Extract:

For a converging lens, the image is always inverted. The size of the image, however, depends on the distance between the object and the vertical axis on the lens. The distance between the principal focus and the lens' vertical axis is the focal length, which we shall denote as f. If the object is at a distance of more than 2f from the lens' vertical axis, the image will be smaller than the object. If the object is at a distance between f and 2f from the lens' vertical axis, the image will be larger than the object. If the object is at a distance of 2f from the lens' vertical axis, the image is the same size as the object. In the question above, it can be seen using a ruler (regardless of the screen you are using) that the object is more than 2f from the lens' vertical axis. This means the image will be inverted and diminished (i.e. smaller).

Describe the image I.

Choose words from the list. Tick (✓) two boxes.

square enlarged

square diminished

square same size

square inverted

square upright

Extended tier only

An endoscope is a piece of medical equipment used to see inside a person's body. Endoscopes use optical fibres within a long tube which reflects light from inside the patient to an eye piece lens or camera.

Fig. 1.1

Fig. 1.1 shows a section of optical fibre. Light travels from X to Y.

On Fig. 1.1, complete the path of the light ray until it leaves the section of optical fibre.

State the type of reflection that occurs within an optical fibre.

Extended tier only

Calculate the critical angle.

Glass has a refractive index of 1.52.

critical angle = ...................................

Extract:

Glass has a refractive index of 1.52.

Extended tier only

When the light ray exits the optical fibre it passes into air.

Calculate the speed of light in glass.

speed of light in glass = ....................................

Fig. 9.1 shows two rays of light X and Y leaving an object O. The rays strike a plane mirror.

Ray X is reflected as shown.

(i) On Fig. 9.1, draw the normal at the point where ray X strikes the mirror.

(ii) On Fig. 9.1, draw the path of ray Y after it strikes the mirror.

An object O is placed on the left of a thin converging lens. F is the principal focus.

This arrangement is shown in Fig. 9.2.

Two rays from the top of the object are incident on the lens, as shown in Fig. 9.2.

On Fig. 9.2, draw the path of each ray to locate the position of the image of O formed by the lens.

On Fig. 9.2, draw an arrow to represent the image and label it I.

Fig. 7.1 shows a converging lens and the image I formed when an object is placed to the left of the lens. The principal focuses are labelled A and B and the centre of the lens is labelled C.

(i) On Fig. 7.1, draw two rays to locate the position of the object.

Draw the object and label it O.

(ii) Ring all of the following distances that are equal to the focal length of the lens.

Fig. 7.2 shows green light passing through a triangular glass block.

Red light enters the triangular glass block shown in Fig. 7.2 along the same path as the green light.

(i) On Fig. 7.2, draw the path of the red light within the triangular glass block.

(ii) Fig. 7.3 shows green light passing through a rectangular glass block.

Red light enters the rectangular glass block shown in Fig. 7.3 along the same path as the green light.

On Fig 7.3 draw the path of the red light within the rectangular glass block.

(iii) On Fig 7.3 draw the path of the red light after leaving the rectangular glass block.

Extended tier only

The speed of a light wave in air is 3.00 × 10⁸ m / s. The refractive index of water is 1.33.

Calculate the speed of the light wave in water.

speed = .........................................................

Fig. 7.1 shows parallel wavefronts of a light wave in air incident on a boundary with a transparent plastic.

On Fig. 7.1,

(i) draw the positions of the four refracted wavefronts in the plastic,

(ii) draw an arrow to show the direction of travel of the refracted wave,

(iii) label the angle of refraction r of the light wave.

Fig. 6.1 shows a mirror periscope. The periscope is used to view a golfer over the heads of other people. The periscope has two plane mirrors each at an angle of 45° to the vertical.

(i) On Fig. 6.1:

1. Continue the ray of light from the golfer towards the upper mirror of the periscope.

• Draw and label the normal at the point where the ray strikes the mirror.

(ii) On Fig. 6.1, continue the ray of light after reflection at the upper mirror until it leaves the periscope.

(iii) State the law of reflection used to deduce the position of the ray of light after striking the mirrors.

Fig. 6.2 shows three rays of red light each entering a semi-circular glass block.

Using the information in Table 6.1, draw on Fig. 6.2 to complete the path of each ray of red light.

Fig. 6.1 shows an arrangement of glass prisms inside a box. The angles of the prisms are 45°, 45° and 90°.

This is a device used to view objects that are behind a wall. The incident ray of light undergoes total internal reflection in the prisms.

On Fig. 6.1, complete the path of the ray through the device and show the ray as it emerges from the box.

Extended tier only

Show that the refractive index of glass with a critical angle of 45° is 1.41.

Fig. 8.1 is a partially completed ray diagram.

The object is at O and its image is at I.

Which distance is the focal length of the lens? Tick one box.

square C to F₁

square O to C

square F₂ to I

square O to I

On Fig. 8.1, extend the two rays from the arrowhead on the object until both reach the position of the image.

Extract:

Fig. 8.1 is a partially completed ray diagram.

The object is at O and its image is at I.

The object is moved a small distance away from the lens. State the effect, if any, this has on the position and size of the image.

Fig. 8.1 shows a ray of light travelling through a glass block and then reflecting from a mirror.

State the term used for the dashed lines drawn in Fig. 8.1.

Extract:

Use Fig. 8.1 to identify the three angles in the list. Place the correct letter in the box to indicate each angle:

Angle of incidence; Angle of reflection; Angle of refraction.

You may be questioning whether angle P is an angle of refraction. It is important to realise that refraction occurs when light enters the block and when light exits the block. In both circumstances, the density of the medium changes and the speed of the light changes. The angle of refraction is the angle between the light ray in the second medium and the normal of the boundary between the two materials, therefore angle P is an angle of refraction.

Use Fig. 8.1 to identify the three angles in the list. Place the correct letter in the box to indicate each angle.

square angle of incidence

square angle of reflection

square angle of refraction

The ray of light in Fig. 8.1 changes direction as it enters the glass block. State the name of this effect and explain why it happens.

A ray of light refracts as it travels from air into glass, as shown in Fig. 8.1.

State which angle *w, x, y *or z, is the angle of refraction.

Extended Tier Only

Fig. 6.1 shows a converging lens and its principal axis. The points F₁ and F₂ are each a principal focus of the lens.

An object O is placed between F₁ and the lens.

(i) On Fig. 6.1, draw two rays from the top of the object O to locate the image. Label the image I.

(ii) The object O is moved to the left along the principal axis so that it is further from the lens than F₁.

Fig. 6.2 is a diagram of the new arrangement with the new image shown.

Underline three of the terms below that describe the image shown in Fig. 6.2.

Fig. 6.3 shows yellow light passing through a glass prism

Blue light enters the prism along the same path as the yellow light.

On Fig. 6.3, draw the path of the blue light as it enters, passes through and leaves the prism.

The water waves travel from deep water into shallow water. The water waves have a lower speed in the shallow water.

Fig. 7.2 shows wavefronts for the waves in deep water to the left of the boundary.

(i) On Fig. 7.2, complete three wavefronts for the waves in shallow water to the right of the boundary.

(ii) State the term for the process at the boundary in Fig. 7.2.

Extended Tier Only

Fig. 7.1 is a full-scale diagram of a small nail N in front of a thin converging lens. The line L represents the lens.

The focal length of the lens is 3.0 cm.

Rays of light, parallel to XY, are travelling towards the lens.

Describe what happens to the light after it passes through the lens.

Extract:

Fig. 7.1 is a full-scale diagram of a small nail N in front of a thin converging lens. The line L represents the lens.

The focal length of the lens is 3.0 cm.

Extended Tier Only

On Fig. 7.1, mark and label with an F each of the two principal focuses of the lens.

Extract:

Fig. 7.1 is a full-scale diagram of a small nail N in front of a thin converging lens. The line L represents the lens. The focal length of the lens is 3.0 cm. Rays of light, parallel to XY, are travelling towards the lens. On Fig. 7.1, the two principal focuses of the lens are marked on XY 3.0 cm from the centre of the lens, one point on the left and one point on the right of the lens, each labelled F. The small nail N, of height 1.2 cm, is positioned 2.0 cm to the left of the lens.

Extended Tier Only

The small nail N, of height 1.2 cm, is positioned 2.0 cm to the left of the lens.

(i) By drawing on Fig. 7.1, find the position of the image I of N and add image I to the diagram.

(ii) State and explain whether I is a real or a virtual image.

(iii) State the name given to a lens when it is used in this way.

Fig. 7.1 represents two rays of light striking a thin converging lens. The rays are both parallel to the principal axis.

F₂ and F₁ are the focal points of the lens.

On Fig. 7.1, continue the path of each ray beyond the lens as far as the screen.

Fig. 7.1 shows a ray of light travelling from the air through a glass block.

Fig. 7.1

(i) State the angle of incidence at the air-to-glass boundary.

(ii) Determine the angle of refraction at the air-to-glass boundary.

(iii) Suggest a value for the incident angle at the glass-to-air boundary, and justify your reasoning.

When the angle of refraction is greater than the critical angle, total internal reflection occurs.

Describe total internal reflection.

Fig 7.2 shows total internal reflection of light in an optical fibre.

Fig. 7.2

The angle $θ$ is 48°.

State the angle of reflection and justify your reasoning.

A student investigates the refraction of light through a rectangular glass block. Fig. 3.1 shows the student's ray-trace sheet.

Fig. 3.1

On Fig. 3.1, draw a normal NL to the side AB of the block at the point S. Continue the normal so that it passes through side CD of the block.

Extract:

A student investigates the refraction of light through a rectangular glass block. Fig. 3.1 shows the student's ray-trace sheet.

A rectangular outline labelled ABCD. Side AB is the top surface. A point S is marked on AB. Below CD there are two points P3 and P4, and an eye symbol in the bottom right corner, indicating perspective.

On Fig. 3.1, draw a normal NL to the side AB of the block at the point S. Continue the normal so that it passes through side CD of the block.

Draw a line RS at an angle $i=40^{\circ}$ to the normal, above AB and to the left of the normal.

Extract:

A student investigates the refraction of light through a rectangular glass block. Fig. 3.1 shows the student's ray-trace sheet.

On Fig. 3.1, draw a normal NL to the side AB of the block at the point S. Continue the normal so that it passes through side CD of the block.

Draw a line RS at an angle i = 40° to the normal, above AB and to the left of the normal.

The student places two pins, $P_{1}$ and $P_{2}$, on the line RS.

(i) On Fig. 3.1, mark the positions of the two pins $P_{1}$ and $P_{2}$. Indicate a suitable distance between the pins for this type of ray-trace experiment.

(ii) Suggest two other techniques that the student can use to produce an accurate ray-trace.

Extract:

A student investigates the refraction of light through a rectangular glass block. Fig. 3.1 shows the student's ray-trace sheet.

A rectangular outline labelled ABCD. Side AB is the top surface. A point S is marked on AB. Below CD there are two points P3 and P4, and an eye symbol in the bottom right corner, indicating perspective.

On Fig. 3.1, draw a normal NL to the side AB of the block at the point S. Continue the normal so that it passes through side CD of the block.

The student observes the images of $P_{1}$ and $P_{2}$ through the side CD of the block. They place two more pins, $P_{3}$ and $P_{4}$, so that they appear to be in a straight line with the images. Fig. 3.1 shows the positions of $P_{3}$ and $P_{4}$.

• Draw a line joining $P_{3}$ and $P_{4}$. Continue the line until it meets the normal NL.
• Label the point T where the line meets side CD. Draw the line ST.
• Measure the angle $r$ between ST and the normal.

Extract:

A student investigates the refraction of light through a rectangular glass block.

Draw a line RS at an angle [i = 40°] to the normal, above AB and to the left of the normal.

The student plans to take more sets of readings to investigate the relationship between $i$ and $r$.

(i) Suggest other suitable values of angle $i$ that the student could use.

(ii) Suggest how the student could improve the experiment to check the reliability of their results.

Light may be totally internally reflected at the boundary between two materials.

(i) State the two conditions necessary for total internal reflection to occur.

(ii) State one practical use of total internal reflection.

Fig. 5.1 shows a ray of light incident on a semicircular glass block.

Fig. 5.1

Explain why the ray does not change direction when it enters the block at the curved edge.

The critical angle for the glass is 42°.

Calculate the refractive index of the glass.

Show your working.

Extract:

Fig. 5.1 shows a ray of light incident on a semicircular glass block.

A semicircular glass block shown from above. A ray of light enters the curved edge and hits the straight edge at an angle of incidence of 50-degrees to the normal. The normal is drawn as a dashed line perpendicular to the straight edge.

The critical angle for the glass is 42°.

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

Extended tier only

A laser produces a beam of monochromatic light. State what is meant by the term monochromatic.

A wave, in air, is incident on a glass block. Fig. 7.1 shows the wavefronts at the air-glass boundary. The arrow shows the direction of travel of the wavefronts.

The wave undergoes reflection and refraction at the air-glass boundary.

On Fig. 7.1 draw:

(i) the wavefronts of the reflected wave

(ii) the wavefronts of the refracted wave.

A transverse wave is produced in a long, horizontal rope. The rope is much longer than the wavelength of the wave.

In the space below, sketch a diagram to show the appearance of the rope as the wave passes along it. Label two important features of the wave.

Fig. 6.1 represents the electromagnetic spectrum.

State the radiation in each of the regions represented by A, B, C and D in Fig. 6.1.

Extended tier only

A source emits visible light.

Fig. 6.2 shows a ray of red light from the source incident on the face XY of a glass prism at point S.

The angle of incidence i of the ray is 35 °. The refractive index of the glass for red light is 1.5.

(i) Calculate the angle of refraction in the glass at S.

angle of refraction = ......................................................... [2]

(ii) On Fig. 6.2, draw the refracted ray at face XY and the ray emerging from face XZ of the prism. Label this ray R.

(iii) A ray of blue light follows the same path as the ray of red light incident on the face XY.

On Fig. 6.2, draw the path of this ray in the prism and emerging from the prism.

Label this ray B.

Extended tier only

Fig. 7.1 shows red light travelling from air into a prism made of diamond. The path of the red light is incomplete.

The refractive index of diamond is 2.42.

Calculate angle x.

angle x = .........................................................

Explain the term total internal reflection.

Extract:

Fig. 7.1 shows red light travelling from air into a prism made of diamond. The path of the red light is incomplete. The refractive index of diamond is 2.42. At the first boundary of air to diamond, the light ray approaches at an angle of 40 degrees to the normal, and leaves the boundary at an angle x to the normal. At the second boundary, diamond to air, the light ray approaches at angle y to the normal.

Explain the term total internal reflection:

• When light travels from an (optically) more dense medium to an (optically) less dense medium;
• And the angle of incidence (of the light at the boundary) is greater than the critical angle (of the material creating the boundary);
• Then all light is reflected OR no light is refracted;

The angle y is greater than the critical angle of diamond.

On Fig. 7.1, draw the path of the red light through and out of the prism after point A.

Fig. 7.1 shows a ray of light in water that is incident on a submerged, transparent plastic block.

State what happens to the speed of light as it enters the plastic block. Explain your answer.

Extended tier only

Fig. 7.2 shows the two principal focuses F₁ and F₂ of a thin converging lens.

Fig. 7.2 also shows an object O of height 1.2cm placed close to the lens. Two rays from the tip of the object O are incident on the lens.

(i) On Fig. 7.2, continue the paths of these two rays for a further distance of at least 5 cm.

(ii) Using your answer to (b)(i), find and mark on Fig. 7.2 the image I of object O and label this image.

(iii) Determine the height of image I.

height = ...........................................................[1]

(iv) State and explain whether I is a real image or a virtual image.

Fig. 7.1 shows a ray of light striking a plane mirror at point P.

(i) Determine the value of the angle of incidence for the ray of light at point P.

angle of incidence = ...................................................... ° [1]

(ii) On Fig. 7.1,

• draw a normal at point P
• draw the ray reflected at point P
• determine the angle of reflection at point P.

angle of reflection = ...................................................... ° [3]

Fig. 7.2 shows an object OB positioned 20cm from a thin converging lens. Both principal focuses of the lens are labelled F.

Two rays from the tip B of the object are incident on the lens, as shown in Fig. 7.2.

On Fig. 7.2, continue the paths of these two rays to show the position of the image of OB formed by the lens. Draw an arrow to show the size, position and orientation of the image of OB.

Fig. 6.1 shows a ray of red light incident on part of a lens.

(i) On Fig. 6.1, continue the path of the ray as it passes through the lens and emerges from it.

(ii) State the term used to describe the process as the ray enters and leaves the lens.

Fig. 6.2 shows two parallel rays of light travelling towards another lens.

The two rays of light pass through the lens to form an image.

On Fig. 6.2, continue the path of the rays. Extend the rays for at least 5 cm beyond the lens.

A ray of light in air is incident on a glass block. The light changes direction.

State

(i) the name of this effect.

(ii) the cause of this effect.

Fig. 5.1 shows a thin converging lens of focal length 3.5cm.

(i) On Fig. 5.1, mark each of the two principal focuses and label each with the letter F.

(ii) An object O of height 4.4cm is placed a distance of 7.5cm from the lens.

On Fig. 5.1, draw rays from the tip of the object O to locate the image. Draw and label the image.

(iii) Determine the height of the image.

height of the image = ...........................................................[1]

(iv) State and explain whether the image is real or virtual.

Fig. 5.1 shows a visible spectrum focused on a screen by passing light from a source of white light through a lens and a prism.

(i) State the name of the process that separates the colours in white light.

(ii) State the colour of the light on the screen at points A and B.

(iii) State the property of the glass of the prism that causes white light to be split into the different colours of the spectrum.

Extended tier only

Fig. 5.2 shows a section of an optical fibre in air. A ray of light is incident on the fibre wall at X.

(i) On Fig. 5.2, continue the path of the ray of light up to the end of the fibre.

(ii) The refractive index of the material of the fibre is 1.46. Calculate the critical angle of the material of the fibre.

critical angle = ...........................................................[2]

(iii) State two uses of optical fibres.