10 GCSE Physics questions about wireless earbuds, from Foundation to Higher, each with a full worked solution. Your phone sends music to the earbuds using Bluetooth, which uses electromagnetic waves (microwaves at about 2.4 GHz). A tiny speaker in each earbud then turns the signal into sound waves – vibrations of the air that travel into your ear.
Course: Combined Science + Separate Physics | Tier: Foundation + Higher | Topics: Waves · Electricity
📌 KEY DEFINITIONS – learn them word for word
Transverse wave: the oscillations are perpendicular to the direction of energy transfer, e.g. electromagnetic waves.
Longitudinal wave: the oscillations are parallel to the direction of energy transfer, e.g. sound waves.
Wavelength: the distance from a point on one wave to the equivalent point on the next wave.
Frequency: the number of waves passing a point each second.
Equations you’ll use
v = f λ | T = 1 ÷ f (given on the equation sheet) | s = v t | Q = I t | E = Q V | E = P t
| Quantity | Symbol | Unit |
|---|---|---|
| wave speed | v | metres per second (m/s) |
| frequency | f | hertz (Hz) |
| wavelength | λ | metres (m) |
| period | T | seconds (s) |
| charge | Q | coulombs (C) |
| current | I | amps (A) |
| energy | E | joules (J) |
| potential difference | V | volts (V) |
| power | P | watts (W) |
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) Bluetooth uses microwaves with a frequency of 2.4 GHz. Calculate their wavelength. (speed = 3.0 × 108 m/s)
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
A: 0.125 m (12.5 cm)
Q2 (F) The earbuds play a note with a frequency of 1000 Hz. The speed of sound in air is 340 m/s. Calculate the wavelength of the sound.
Show solution
F: v = f λ
I: 340 = 1000 × λ
F: λ = 340 ÷ 1000
A: 0.34 m
Q3 (F) Calculate the period of a 500 Hz sound wave.
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) When fully charged, each earbud battery can supply a current of 50 mA for 1 hour. The battery has a potential difference of 3.7 V. Calculate the charge stored in coulombs and the energy stored.
Show solution
Convert first: 50 mA = 0.050 A; 1 hour = 3600 s
Charge: Q = I t = 0.050 × 3600 = 180 C
Energy: E = Q V = 180 × 3.7 = 666 J
Q5 (F/H) Playing music, an earbud uses an average power of 0.037 W. Calculate how long the 666 J battery lasts, in hours.
Show solution
F: E = P t
I: 666 = 0.037 × t
F: t = 666 ÷ 0.037 = 18 000 s
A: 18 000 ÷ 3600 = 5.0 hours
Q6 (F/H) The Bluetooth signal and the sound from the earbud are both waves. Give two differences between them. [2 marks]
Show answer
Any two:
• Bluetooth is an electromagnetic wave; sound is a mechanical wave (it needs a medium)
• Bluetooth is transverse; sound is longitudinal
• Bluetooth travels at 3 × 108 m/s; sound travels at about 340 m/s in air
• Bluetooth can travel through a vacuum; sound cannot
Q7 (F/H) Turning the volume up and playing a higher note both change the sound wave. Describe how. [2 marks]
Show answer
• louder sound = larger amplitude
• higher note (higher pitch) = higher frequency (and so a shorter wavelength)
Q8 (F/H) The charging case recharges an earbud with a current of 0.10 A for 30 minutes. Calculate the charge supplied. Is this enough to fully charge the 180 C battery?
Show solution
Convert first: 30 minutes = 1800 s
F: Q = I t
I: Q = 0.10 × 1800
F: Q is already the subject
A: 180 C – yes, exactly enough (if no energy is wasted)
Q9 (H) Your phone is 10 m away. Calculate how long a Bluetooth signal takes to travel 10 m, and how long a sound wave would take. (radio: 3.0 × 108 m/s; sound: 340 m/s)
Show solution
Bluetooth: t = s ÷ v = 10 ÷ 3.0 × 108 = 3.3 × 10−8 s
Sound: t = 10 ÷ 340 = 0.029 s
The electromagnetic wave is almost a million times faster.
Q10 (H) Calculate the period of a 2.4 GHz Bluetooth wave. Give your answer in standard form.
Show solution
F: T = 1 ÷ f
I: T = 1 ÷ 2.4 × 109
F: T is already the subject
A: 4.2 × 10−10 s (2 s.f.)
⚠️ Where students lose marks
- Using the speed of sound (340 m/s) for Bluetooth signals. All electromagnetic waves travel at 3 × 108 m/s.
- Forgetting to change GHz to Hz or mA to A.
- Saying sound waves are transverse. Sound is longitudinal.
- Mixing up amplitude (loudness) and frequency (pitch).
More devices: all 40 everyday devices · Waves · Electricity
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