Uses and applications of electromagnetic waves

Compare — 5 marks

A hospital uses two different types of electromagnetic waves for medical imaging. Department A uses infrared radiation to monitor a patient's skin temperature during surgery. Department B uses X-rays to take images of a patient's broken bone.

(a) Compare the wavelengths of infrared radiation and X-rays. [2 marks]
(b) Compare how infrared radiation and X-rays interact with human tissue. [2 marks]
(c) Explain why X-rays are more suitable than infrared radiation for imaging bones inside the body. [1 mark]

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(a) X-rays have a shorter wavelength than infrared radiation
(a) Infrared radiation has a longer wavelength than X-rays
(b) Infrared radiation is absorbed by the skin/surface tissue and causes heating
(b) X-rays penetrate through soft tissue but are absorbed by dense material like bone
(c) X-rays can pass through soft tissue but are stopped/absorbed by bone, creating a clear image of the bone structure

Calculate — 2 marks

Mobile phones use microwaves to send and receive signals from transmission towers. A mobile phone transmits signals at a frequency of 900 MHz. The speed of microwaves is 3.0 × 10⁸ m/s.

(a) Calculate the wavelength of the microwaves. [1 mark]
(b) A transmission tower is located 15 km away from the phone. Calculate the time taken for the signal to travel this distance. [1 mark]

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(a) λ = v ÷ f or substitution: 3.0 × 10⁸ ÷ 900 000 000
(a) 0.33 m or 0.3 m
(b) time = distance ÷ speed or substitution: 15 000 ÷ 3.0 × 10⁸
(b) 5.0 × 10⁻⁵ s or 0.00005 s

Explain — 3 marks

Satellite dishes receive television signals from communications satellites in space. The satellites transmit microwaves to Earth.

(a) Explain why microwaves are used to transmit television signals from satellites. [2 marks]
(b) Explain why the satellite dish must be pointed in a specific direction to receive the signal. [1 mark]

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(a) microwaves can travel long distances through space
(a) microwaves penetrate the atmosphere / microwaves can carry large amounts of information
(b) microwaves travel in straight lines / need line of sight to the satellite

Describe — 2 marks

A student uses a mobile phone to call a friend. The phone sends signals using electromagnetic waves.

(a) State the type of electromagnetic wave used to transmit mobile phone signals. [1 mark]
(b) Describe one other use of this type of electromagnetic wave. [1 mark]

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(a) microwaves
(b) cooking/heating food (in a microwave oven)
(b) satellite communications
(b) radar systems
(b) WiFi/bluetooth signals

Evaluate — 3 marks

A local council is considering whether to allow a new mobile phone mast to be built in a residential area. The mast would use microwave radiation to improve mobile phone signal for the community. Some residents have expressed concerns about possible health effects from continuous exposure to low-level microwave radiation.

(a) State one different use of microwaves. [1 mark]
(b) Evaluate whether the council should approve the phone mast. You should consider both the benefits of improved mobile signal and any potential risks from microwave radiation. [2 marks]

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(a) Cooking/heating food in microwave ovens
(a) Satellite communications / satellite TV transmission
(a) Wi-Fi / Bluetooth technology
(a) Radar systems for navigation
(b) Benefit identified: reliable communication / emergency calls / internet access / economic advantages
(b) Risk identified: microwaves can heat body tissue / concerns about long-term exposure effects

Uses and applications of electromagnetic waves

Compare — 5 marks

Calculate — 2 marks

Explain — 3 marks

Describe — 2 marks

Evaluate — 3 marks

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