Light & the Electromagnetic Spectrum — Drills · Grade 8 Science

Chapter: Waves, Sound & Light

What these drills covers

By the end of Light & the Electromagnetic Spectrum you should be able to:

8 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: electromagnetic (EM) wave, electromagnetic spectrum, reflection, absorption, transmission, model, evidence, system boundary, assumption.

Problem 1

Which travels fastest in a vacuum?
  1. Sound
  2. Visible light
  3. Both the same
  4. Neither travels
Answer and explanation

Visible light

Light needs no medium and travels at about 3 × 10⁸ m/s; sound cannot travel at all.

Problem 2

Which has the longest wavelength?
  1. Gamma rays
  2. X-rays
  3. Visible light
  4. Radio waves
Answer and explanation

Radio waves

Radio waves sit at the long-wavelength, low-frequency end of the spectrum.

Problem 3

Which carries the most energy per wave?
  1. Radio
  2. Infrared
  3. Visible
  4. Gamma
Answer and explanation

Gamma

Energy rises with frequency, and gamma rays have the highest frequency.

Problem 4

Light bending as it passes from air into water is
  1. reflection
  2. refraction
  3. absorption
  4. diffraction
Answer and explanation

refraction

Refraction is the change of direction caused by a change in speed between media.

Problem 5

A red object looks red because it
  1. absorbs red and reflects the rest
  2. reflects red and absorbs the rest
  3. emits red light
  4. transmits all colours
Answer and explanation

reflects red and absorbs the rest

The colour you see is the light reflected to your eye.

Problem 6

Light travels at about 3 × 10⁸ m/s. How many metres does it travel in 2 seconds, expressed in hundreds of millions?
Answer and explanation

6

3 × 10⁸ × 2 = 6 × 10⁸ m, or six hundred million metres.

Problem 7

Explain what all parts of the electromagnetic spectrum have in common and what distinguishes them.
Answer and explanation

All are electromagnetic waves, all travel at the same speed in a vacuum, and none needs a medium. They differ in frequency and wavelength, which together determine their energy and therefore how they interact with matter — radio waves pass through walls, visible light reflects off them, and gamma rays penetrate and can damage living tissue.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 8

Explain why ultraviolet light can damage skin while visible light generally does not.
Answer and explanation

Ultraviolet has a higher frequency than visible light, so each wave carries more energy — enough to break chemical bonds in molecules within skin cells, including DNA. Visible light carries too little energy per wave to do that, so it is absorbed and largely converted to heat instead. The difference is in energy per wave rather than in brightness.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

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