Practice questions · Regions and uses

Order, uses, and one constant speed.

Seven original Cambridge-style questions. They drill the order of the spectrum, the use of each region, the rule that all EM waves share one speed, and a wave-speed calculation.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

What the spectrum questions reward

Know the order. Pair each region with a use. Hold the speed constant.

Order: radio, microwave, infrared, visible, ultraviolet, X-ray, gamma (longest to shortest wavelength).
Speed: all EM waves travel at 3.0 x 10^8 m/s in a vacuum. Only wavelength and frequency change.
Equation: v = f x wavelength, so wavelength = v / f.

[2 marks]

List the seven regions of the electromagnetic spectrum in order, starting with the region that has the longest wavelength.

Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays. ✓✓

This is also the order of increasing frequency. Longest wavelength means lowest frequency.

[2 marks]

State two properties that all electromagnetic waves have in common.

They are all transverse waves. ✓
They all travel at the same speed in a vacuum, 3.0 x 10^8 m/s. ✓

Other acceptable answers: they can all travel through a vacuum, and they all transfer energy.

Calculation

[3 marks]

A mobile phone communicates using microwaves of wavelength 0.15 m. Calculate the frequency of these microwaves. (speed of EM waves = 3.0 x 10^8 m/s)

Rearrange: v = f x wavelength, so f = v / wavelength

f = (3.0 x 10^8) / 0.15

f = 2.0 x 10^9 Hz

That is 2.0 GHz, a typical mobile phone frequency. The answer is sensible.

[4 marks]

State a typical use for each of the following regions of the electromagnetic spectrum:

(a) radio waves, [1] (b) infrared, [1] (c) ultraviolet, [1] (d) gamma rays. [1]

(a) Television or radio broadcasting. ✓

(b) Remote controllers, intruder alarms, or thermal imaging. ✓

(d) Sterilising equipment and food, or treating cancer. ✓

[2 marks]

Of all the regions of the electromagnetic spectrum, state which has:

(a) the highest frequency, [1] (b) the longest wavelength. [1]

(a) Gamma rays. ✓

(b) Radio waves. ✓

Highest frequency and shortest wavelength go together (gamma). Lowest frequency and longest wavelength go together (radio).

Analysis

[2 marks]

A student says that because gamma rays carry far more energy than radio waves, they must travel much faster. Explain why this is wrong.

All electromagnetic waves travel at the same speed in a vacuum, 3.0 x 10^8 m/s, regardless of their energy. ✓
Gamma rays differ from radio waves by having a much shorter wavelength and higher frequency, not a higher speed. ✓

Analysis

[3 marks]

Identify the region of the electromagnetic spectrum used in each case, and you do not need to explain.

(a) Sending a television picture from a satellite to a home dish. [1] (b) Taking an image of a broken bone in a hospital. [1] (c) Changing channels with a television remote control. [1]

(a) Microwaves. ✓

(b) X-rays. ✓

Satellite and mobile signals, microwaves. Bones and airport scanners, X-rays. Remotes and alarms, infrared.

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.