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CIE iGCSE Co-Ordinated Science P3.2.4 Dispersion of light Exam Style Questions Paper 3

CIE iGCSE Co-Ordinated Science Paper 3 - All Chapters

Question

(a) Fig. 12.1 shows the circuit symbols for three electrical components, X, Y and Z, used in an electric torch (flashlight).
(i) Complete Fig. 12.1 to identify each component.
(ii) Using the symbols in Fig. 12.1, draw the circuit diagram for the torch.
(iii) The current in component Z is 0.50 A. The voltage supplied by component X is 1.5 V. Calculate the resistance of component Z.
(b) Fig. 12.2 shows a single ray of light from the torch reflected by a mirror.
(i) State the name of the dotted line AB.
(ii) On Fig. 12.2, label the angle of incidence with the letter \(i\).
(iii) The angle of incidence is 40°. State the angle of reflection.
(c) Fig. 12.3 shows a single ray of white light from the torch passing into a glass prism.
Complete Fig. 12.3 to show what happens to the light as it passes through and out of the prism.

Topic codes:

• Topic P4.3.1 — Circuit diagrams and circuit components (Part (a)(i) & (a)(ii))
• Topic P4.2.4 — Resistance (Part (a)(iii))
• Topic P3.2.1 — Reflection of light (Part (b)(i), (b)(ii) & (b)(iii))
• Topic P3.2.4 — Dispersion of light (Part (c))

▶️ Answer/Explanation

(a)(i) X is a cell; Y is a switch; Z is a lamp
The cell provides the electrical energy (voltage). The switch controls the flow of current by opening or closing the circuit. The lamp (bulb) converts electrical energy into light and heat energy.

(a)(ii) All 3 components connected in series
In a simple torch circuit, the cell, switch, and lamp are connected in series so that current flows through all components in a single loop. When the switch is closed, the circuit is complete and the lamp lights up.

(a)(iii) Resistance = 3.0 Ω
Using Ohm’s law: \(R = \frac{V}{I}\)
\(R = \frac{1.5}{0.50} = 3.0\) Ω

(b)(i) Normal
The normal is an imaginary line drawn perpendicular (at 90°) to the reflecting surface at the point where the incident ray strikes the mirror.

(b)(ii) Angle of incidence labelled correctly
The angle of incidence is the angle between the incident ray and the normal. It should be labelled with the letter \(i\) between the incoming ray and the normal line AB.

(b)(iii) Angle of reflection = 40°
According to the law of reflection, the angle of incidence equals the angle of reflection. Both angles are measured from the normal. Therefore, if the angle of incidence is 40°, the angle of reflection is also 40°.

(c) Correct refraction through and out of the prism; dispersion shown on entry to the prism
When white light enters a glass prism, it slows down and bends (refracts). Different colours of light have different wavelengths and are refracted by different amounts, causing the white light to split into its component colours (dispersion). The spectrum is produced in the order: red, orange, yellow, green, blue, indigo, violet. The ray diagram should show:

  • The ray bending towards the normal when entering the prism (from air to glass)
  • The ray spreading into a spectrum (dispersion) at the first surface
  • Each colour ray bending away from the normal when exiting the prism (from glass to air)

Question

(a)
(i) The Sun consists mostly of two elements. State the names of these two elements.
(ii) The Milky Way galaxy contains the Sun and many other stars. State the approximate diameter of the Milky Way.
(iii) Stars are extremely hot bodies. Energy is being transferred from the stars into space when they emit electromagnetic radiation. Explain why stars can lose energy by radiation and not by conduction or convection.
(iv) Visible light waves from a distant star change direction as they enter the Earth’s atmosphere. State the name of this effect.
(b)
(i) A frequency of infrared radiation emitted by the Sun is \(2.5 \times 10^{14} \, \text{Hz}\). The speed of infrared radiation is \(3.0 \times 10^8 \, \text{m/s}\). Calculate the wavelength of this infrared radiation.
(ii) Fig. 10.1 shows an incomplete electromagnetic spectrum. Write infrared radiation in its correct position.
(c) Fig. 10.2 shows a ray of white light from the Sun refracting through a prism.
The ray of light splits into the seven colours of the visible spectrum.
The seven colours are shown as the numbers 1 to 7.
Red light refracts less than violet light.
Complete Table 10.1 to identify the seven colours.
(d) Fig. 10.3 shows a spacecraft on a rocket about to be launched.
(i) The weight of the spacecraft and the rocket is 6,000,000 N.
When the rocket engines start to operate, the upward force exerted by the rocket engines is 9,000,000 N.
Calculate the resultant upward force on the spacecraft and the rocket.
(ii) The rocket accelerates as it leaves the ground. State what is meant by accelerate.
(iii) State two energy stores in which the energy stored is increasing as the rocket accelerates upwards.

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic P6.2.1 — The Sun as a star (Parts (a)(i), (a)(ii), (a)(iii))
• Topic P3.3 — Electromagnetic spectrum (Parts (a)(iv), (b)(i), (b)(ii))
• Topic P3.2.4 — Dispersion of light (Part (c))
• Topic P1.5.1 — Effects of forces (Part (d)(i))
• Topic P1.2 — Motion (Part (d)(ii))
• Topic P1.6.1 — Energy (Part (d)(iii))

▶️ Answer/Explanation

(a)(i) hydrogen and helium

The Sun is composed primarily of hydrogen (about 73%) and helium (about 25%). Nuclear fusion reactions in the Sun’s core convert hydrogen into helium, releasing vast amounts of energy.

(a)(ii) 100,000 light-years

The Milky Way galaxy has an approximate diameter of 100,000 light-years. It contains billions of stars, including our Sun.

(a)(iii) Conduction and convection require a medium (matter) to transfer energy, but space is a vacuum.

Conduction requires particles to collide and transfer energy, while convection requires a fluid (liquid or gas) to circulate. Since space is mostly empty (a vacuum), neither conduction nor convection can occur. Radiation, however, does not require a medium and can travel through empty space.

(a)(iv) refraction

When light from a distant star enters the Earth’s atmosphere, it changes speed and direction due to the different densities of air layers. This bending of light is called refraction.

(b)(i) \(1.2 \times 10^{-6} \, \text{m}\)

Using the wave equation: \(\text{speed} = \text{frequency} \times \text{wavelength}\)

Wavelength \(= \frac{\text{speed}}{\text{frequency}} = \frac{3.0 \times 10^8}{2.5 \times 10^{14}} = 1.2 \times 10^{-6} \, \text{m}\).

(b)(ii) Infrared radiation in the box to the right of ‘visible light’

In the electromagnetic spectrum, the order from low frequency to high frequency is: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays. Therefore, infrared should be placed between radio waves and visible light.

(c) The seven colours in order from least refracted to most refracted:

Red light has the longest wavelength and is refracted the least, so it appears at the top of the spectrum (ray 1). Violet light has the shortest wavelength and is refracted the most, appearing at the bottom (ray 7). The mnemonic “ROYGBIV” helps remember the order.

(d)(i) 3,000,000 N

Resultant force = upward force − weight = 9,000,000 − 6,000,000 = 3,000,000 N upwards.

(d)(ii) Acceleration means an increase in speed or velocity.

Specifically, acceleration is the rate of change of velocity. In this context, the rocket’s speed is increasing as it leaves the ground.

(d)(iii) gravitational potential (GPE) and kinetic energy

As the rocket accelerates upwards, it gains height (increasing gravitational potential energy) and increases its speed (increasing kinetic energy). Thermal energy may also increase due to friction with the atmosphere, but GPE and kinetic are the two main stores that increase.

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