S4 Physics Practice Paper: Waves, Light and Heat (100 marks)

2026-11-10

S4 Physics · Waves, optics and heat

S4 Physics Practice Paper: Waves, Light and Heat (100 marks): 6 questions, 26 parts, 100 marks, 75 minutes. Covers wave speed, sound, refraction, lenses and heat.

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Section A — Properties of waves

Show your working and state the unit.

#	Question	Answer and marking notes
1	A wave has a frequency of 50 Hz and a wavelength of 4 m. Find its speed.	Speed = frequency × wavelength = 50 × 4 = 200 m/s
2	Find the period of this wave.	Period = 1 ÷ frequency = 1 ÷ 50 = 0.02 s
3	How long does the wave take to travel 60 m?	Time = distance ÷ speed = 60 ÷ 200 = 0.3 s
4	If the frequency rises to 100 Hz and the speed stays the same, find the new wavelength.	Wavelength = speed ÷ frequency = 200 ÷ 100 = 2 m

Section B — Sound waves and echoes

Take the speed of sound as 340 m/s. State the unit.

#	Question	Answer and marking notes
5	Sound travels at 340 m/s in air. Find the wavelength of a 170 Hz sound wave.	Wavelength = speed ÷ frequency = 340 ÷ 170 = 2 m
6	A ship receives the echo from the seabed 0.6 s after sending a signal. Find the depth.	Depth = 340 × 0.6 ÷ 2 = 102 m (the pulse travels there and back)
7	What frequency range is ultrasound? What range can the human ear hear?	Ultrasound is above 20 000 Hz; the human ear hears roughly 20 Hz to 20 000 Hz.
8	The same 170 Hz sound enters water, where the speed is 1500 m/s. Find its wavelength (3 significant figures).	Wavelength = 1500 ÷ 170 = 8.82 m

Section C — Refraction and total internal reflection

Take the speed of light in vacuum as 3.0 × 10⁸ m/s; give angles to 1 decimal place.

#	Question	Answer and marking notes
9	A glass has a refractive index of 1.5. Find the speed of light in the glass.	Speed = 3.0 × 10⁸ ÷ 1.5 = 2.0 × 10⁸ m/s
10	Light in air strikes water (refractive index 1.33) at an angle of incidence of 45°. Find the angle of refraction.	sin r = sin 45° ÷ 1.33 = 0.532; r = 32.1°
11	A ray hits a plane mirror at an angle of incidence of 30°. Find the angle of reflection and the angle between the incident and reflected rays.	Angle of reflection = 30°; angle between the rays = 180° − 2 × 30° = 120°
12	State the two conditions for total internal reflection.	(1) The light travels from a denser to a less dense medium; (2) the angle of incidence exceeds the critical angle.
13	Find the critical angle of the glass (refractive index 1.5).	sin C = 1 ÷ 1.5 = 0.667; C = 41.8°

Section D — Images formed by a convex lens

Use the lens formula; give the sign and the unit.

#	Question	Answer and marking notes
14	A convex lens has a focal length of 10 cm. An object is 30 cm from the lens. Find the image distance.	1 ÷ v = 1 ÷ 10 − 1 ÷ 30; v = 15 cm
15	Find the magnification.	Magnification = v ÷ u = 15 ÷ 30 = 0.5
16	State three properties of this image.	Inverted, real and diminished (magnification less than 1).
17	The object is moved to 5 cm from the lens. Find the image distance and magnification, and describe the image.	1 ÷ v = 1 ÷ 10 − 1 ÷ 5 = −1 ÷ 10; v = −10 cm (virtual); magnification = 10 ÷ 5 = 2; the image is upright, magnified and virtual.

Section E — Specific heat capacity and the method of mixtures

Take 4200 J kg⁻¹ °C⁻¹ for water and 900 J kg⁻¹ °C⁻¹ for aluminium; show your working.

#	Question	Answer and marking notes
18	How much energy is needed to heat 0.5 kg of water from 20 °C to 60 °C?	Energy = 0.5 × 4200 × (60 − 20) = 84 000 J
19	How long would a 700 W heater take to supply this energy?	Time = 84 000 ÷ 700 = 120 s
20	A 0.2 kg aluminium block at 100 °C is put into 0.5 kg of water at 20 °C. Assuming no heat loss, find the final temperature.	0.2 × 900 × (100 − θ) = 0.5 × 4200 × (θ − 20); θ = 60 000 ÷ 2280 = 26.3 °C
21	The same heater actually took 150 s to do the heating in question 18. Find its efficiency.	Efficiency = 84 000 ÷ (700 × 150) = 84 000 ÷ 105 000 = 80%
22	Explain why water is often used as a coolant.	Water has a high specific heat capacity, so it warms up little for a given energy input and can carry away more heat.

Section F — Latent heat and heat transfer

Take the specific latent heat of fusion as 3.34 × 10⁵ J kg⁻¹ and of vaporisation as 2.26 × 10⁶ J kg⁻¹.

#	Question	Answer and marking notes
23	How much energy is needed to melt 0.2 kg of ice at 0 °C completely?	Energy = 0.2 × 3.34 × 10⁵ = 66 800 J
24	How much energy is needed to boil away 0.1 kg of water at 100 °C?	Energy = 0.1 × 2.26 × 10⁶ = 226 000 J
25	A cup of ice and water (some ice still unmelted) is left at room temperature. Why does its temperature stay at 0 °C?	The energy absorbed changes the state of the ice (latent heat of fusion), so the temperature stays at 0 °C until all the ice melts.
26	In winter a metal handrail feels colder than a wooden one at the same temperature. Explain.	Metal conducts heat faster, so it removes energy from the hand more quickly and feels colder.

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