10 GCSE Physics questions about the smart speaker that get harder as you go, from Foundation to Higher, each with a full worked solution. A smart speaker turns electrical signals into sound by making a cone vibrate. It talks to the internet using Wi-Fi, which uses radio waves, and it stays on standby all day so it can hear its wake word.
Course: Combined Science + Separate Physics | Tier: Foundation + Higher | Topics: Waves, Electricity, Energy
📌 KEY DEFINITIONS – learn them word for word
Longitudinal wave: a wave where the oscillations are parallel to the direction of energy transfer, for example sound. It has compressions and rarefactions.
Frequency: the number of waves passing a point each second, measured in hertz (Hz).
Wavelength: the distance from a point on one wave to the equivalent point on the next wave.
Period: the time taken for one complete wave to pass a point.
Equations you’ll use
| Quantity | Symbol | Unit |
|---|---|---|
| wave speed | v | metres per second (m/s) |
| frequency | f | hertz (Hz) |
| wavelength | λ | metres (m) |
| period | T | seconds (s) |
| power | P | watts (W) |
| energy transferred | E | joules (J) |
| potential difference | V | volts (V) |
| current | I | amps (A) |
Use FIFA for every answer
- F – Formula: write the equation as it appears on the sheet.
- I – Insert: put in the numbers (convert to standard units first).
- F – Fix: rearrange to make the unknown the subject.
- A – Answer: calculate and always give the unit.
Questions
Q1 (F) Describe how the speaker produces a sound wave that travels to your ear. (3 marks)
Show answer
Marking points:
• The speaker cone vibrates (moves backwards and forwards) (1)
• This makes the air particles vibrate, creating compressions and rarefactions (1)
• The sound is a longitudinal wave that transfers energy through the air to your ear (1)
Q2 (F) The speaker plays a note with a frequency of 1000 Hz. The speed of sound in air is 340 m/s. Calculate the wavelength.
Show solution
F: v = f λ
I: 340 = 1000 × λ
F: λ = 340 ÷ 1000
A: 0.34 m
Q3 (F) A note has a frequency of 500 Hz. Calculate its period.
Show solution
F: T = 1 ÷ f
I: T = 1 ÷ 500
F: T is already the subject
A: 0.002 s (2 ms)
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Q4 (F) A deep bass note from the speaker has a frequency of 50 Hz. Calculate its wavelength. (speed of sound = 340 m/s)
Show solution
F: v = f λ
I: 340 = 50 × λ
F: λ = 340 ÷ 50
A: 6.8 m – longer than most living rooms!
Q5 (F/H) The speaker connects to Wi-Fi using radio waves with a frequency of 2.4 GHz. Radio waves travel at 3.0 × 108 m/s. Calculate the wavelength in centimetres.
Show solution
Convert first: 2.4 GHz = 2.4 × 109 Hz
F: v = f λ
I: 3.0 × 108 = 2.4 × 109 × λ
F: λ = (3.0 × 108) ÷ (2.4 × 109) = 0.125 m
A: 12.5 cm
Q6 (F/H) On standby the speaker uses 2.0 W, all day, every day. Electricity costs 25p per kWh. Calculate the cost of standby for one year (365 days).
Show solution
Convert first: 2.0 W = 0.0020 kW; 1 year = 365 × 24 = 8760 h
F: E = P t
I: E = 0.0020 × 8760
A: E = 17.52 kWh
Cost: 17.52 × 25p = 438p = £4.38
Q7 (F/H) You sit 5.1 m from the speaker. Calculate how long it takes the sound to reach you. (speed of sound = 340 m/s)
Show solution
F: s = v t
I: 5.1 = 340 × t
F: t = 5.1 ÷ 340
A: 0.015 s (15 ms)
Q8 (F/H) When playing music, the speaker runs from a 12 V supply with a current of 0.50 A. Calculate the energy transferred in 2 hours.
Show solution
Step 1 – power: P = V I = 12 × 0.50 = 6.0 W
Convert: 2 hours = 2 × 3600 = 7200 s
F: E = P t
I: E = 6.0 × 7200
A: 43 200 J
Q9 (H) Sound waves and Wi-Fi radio waves both carry information to and from the smart speaker. Compare these two types of wave. (4 marks)
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Marking points (any four):
• Sound is longitudinal; radio waves are transverse (1)
• Sound needs a medium (particles) to travel through; radio waves can travel through a vacuum (1)
• Radio waves are much faster (3.0 × 108 m/s compared with about 340 m/s in air) (1)
• Radio waves are electromagnetic; sound is a mechanical wave (1)
• Both transfer energy and information without transferring matter (1)
Q10 (H) The speaker receives 6.0 W of electrical power but gives out only 0.060 W as sound. Calculate its efficiency as a percentage, and explain what happens to the wasted energy.
Show solution
F: efficiency = useful power output ÷ total power input
I: efficiency = 0.060 ÷ 6.0
A: 0.010 = 1%
The other 99% is dissipated, mainly heating the speaker’s coil, magnet and electronics, and then the surroundings. Loudspeakers are surprisingly inefficient!
⚠️ Where students lose marks
- Forgetting to convert GHz or kHz to Hz before using v = f λ.
- Mixing up frequency and period – remember T = 1 ÷ f.
- Describing sound as transverse. Sound is longitudinal: the air particles vibrate in the same direction the wave travels.
- Leaving standby power in watts and time in hours, then calling the answer kWh. Convert W to kW first.
More devices: all 40 everyday devices · Waves · Electricity
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