The questions are on the electromagnetic spectrum test. Take it under real conditions before reading the mark scheme.
Quick answer: The electromagnetic spectrum is the family of transverse waves that all travel at 3.0 × 10⁸ m/s in a vacuum, from radio waves through visible light to gamma rays. This mark scheme gives the model answers and the marks for the 9 questions of the grade 8 science test on electromagnetic spectrum, from ordering waves to mobile signal, with the equivalent answers to accept.
Use these model answers and the marking notes to score your test. Give a mark only for the points that are written, and use the notes to see which part of the chapter to revise.
Level: Grade 8 science (Year 9 · Class 8) · Curriculum: MS-PS4-3
Question 1 Ordering waves (2 marks)
- Microwaves, visible light, X-rays.
- Microwaves.
Marking: (a) 1 mark for the correct order; (b) 1 mark for microwaves.
Question 2 Radio wave calculation (3 marks)
- v = f × λ.
- f = v ÷ λ = 3.0 × 10⁸ ÷ 2.0 = 1.5 × 10⁸ Hz.
Marking: (a) 1 mark; (b) 1 mark for substitution, 1 mark for 1.5 × 10⁸ Hz with unit.
Question 3 Uses of waves (2 marks)
- For example a TV remote control or a thermal camera.
- For example sterilising water or checking security markings.
Marking: 1 mark for each valid use.
Question 4 Danger of X-rays (2 marks)
- X-rays are ionising, so they can knock electrons out of atoms and damage the DNA in cells, which may cause cancer.
- Lead absorbs X-rays, so it stops them reaching the radiographer.
Marking: (a) 1 mark for ionising and damages cells; (b) 1 mark for lead absorbs X-rays.
Question 5 Noisy digital signal (3 marks)
- 10011010.
- Every pulse is clearly above or below the threshold, so the receiver can still decide whether each is a 1 or a 0.
- Noise can be removed from a digital signal by regeneration (or digital signals carry more information).
Marking: (a) 1 mark; (b) 1 mark; (c) 1 mark.
Question 6 Binary (3 marks)
- 8 + 0 + 0 + 1 = 9.
- 14 = 8 + 4 + 2, so 1110.
- 2³ = 8 values.
Marking: 1 mark for each correct answer.
Question 7 Speed of gamma rays (2 marks)
All EM waves travel at the same speed, 3.0 × 10⁸ m/s, in a vacuum. Gamma rays differ from radio waves in having a higher frequency and a shorter wavelength, not a higher speed.Marking: 1 mark for the same speed; 1 mark for higher frequency and shorter wavelength as the real difference.
Question 8 Radar pulse (2 marks)
Distance there and back = 2 × 15 000 = 3.0 × 10⁴ m. Time = 3.0 × 10⁴ ÷ 3.0 × 10⁸ = 1.0 × 10⁻⁴ s.Marking: 1 mark for doubling the distance; 1 mark for 1.0 × 10⁻⁴ s with unit.
Question 9 Mobile signal (1 mark)
Microwaves.Marking: 1 mark for microwaves.
