Answers · Light and the electromagnetic spectrum

Light and the electromagnetic spectrum — return questions key

Check meaning, not exact wording. These are teaching points, not official Cambridge marks.

1. UR1 · Return

Model answer. (a) The light is refracted as it enters and as it leaves the prism, each colour by a different amount, violet most and red least, so the white light spreads into a band of colours: the visible spectrum. This is dispersion. (b) In order of increasing frequency: red, orange, yellow, green, blue, indigo, violet. (c) In order of increasing wavelength: gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves, radio waves. (d) Monochromatic light is light of a single frequency.

A full answer includes

(a) It is refracted, each colour by a different amount, and spreads into a band of colours (dispersion); violet is refracted most, red least.
(b) Red, orange, yellow, green, blue, indigo, violet.
(c) Gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves, radio waves.
(d) Supplement: light of a single frequency.

Also accept

(a) dispersion: each colour refracted differently (b) red … violet (c) gamma rays … radio waves (d) one frequency

Watch for

“In order of increasing frequency the colours run from violet to red.” — Red has the lowest frequency, so increasing frequency runs from red to violet.

2. UR2 · Return

Model answer. (a) All electromagnetic waves travel at the same speed in a vacuum. (b) That speed is 3.0 × 10⁸ m/s, and in air it is approximately the same. (c) Microwaves heat food in microwave ovens and carry mobile phone calls and satellite television; ultraviolet detects fake bank notes, marks property and sterilises water; gamma rays sterilise food and medical equipment and are used to detect and treat cancer. (d) X-rays pass deep into the body and can cause mutation of, or damage to, its cells.

A full answer includes

(a) Their speed.
(b) Supplement: 3.0 × 10⁸ m/s; approximately the same in air.
(c) For example: microwaves, microwave ovens (or mobile phones, satellite television); ultraviolet, detecting fake bank notes (or security marking, sterilising water); gamma rays, sterilising food and medical equipment (or detecting and treating cancer).
(d) Mutation or damage to cells in the body.

Also accept

(a) speed (b) 3.0 × 10⁸ m/s; about the same in air (c) e.g. ovens; bank notes; sterilising (d) mutation or cell damage

Watch for

“Their frequency is the same.” — The frequency changes from region to region; the speed in a vacuum is the same.