Light & the Electromagnetic Spectrum — Practice · Grade 12 Science
Chapter: Waves, Sound & OpticsWhat this practice covers
By the end of Light & the Electromagnetic Spectrum you should be able to:
- I can describe light as an electromagnetic wave and order the spectrum by wavelength, frequency, and energy using c = f λ.
- I can explain wave-particle duality and calculate a photon's energy with E = h f.
10 questions, numeric, multiple choice and written answer, each with a worked explanation.
Vocabulary used: electromagnetic (EM) wave, electromagnetic spectrum, speed of light (c), photon, wave-particle duality, Planck's constant (h).
Problem 1
Answer and explanation
5 m
λ = c ÷ f = (3 × 10⁸) ÷ (6 × 10⁷) = 5 m.
Problem 2
- visible light
- gamma rays
- radio waves
- infrared
Answer and explanation
gamma rays
Gamma rays sit at the short-wavelength end of the spectrum, giving them the highest frequency and energy.
Problem 3
- a longitudinal wave
- a sound wave
- a stream of particles called photons
- a purely continuous wave
Answer and explanation
a stream of particles called photons
The photoelectric effect requires the particle (photon) model: energy arrives in discrete packets whose energy depends on frequency.
Problem 4
Answer and explanation
6.63e-19 J
E = h f = (6.63 × 10⁻³⁴) × (1 × 10¹⁵) = 6.63 × 10⁻¹⁹ J.
Problem 5
Answer and explanation
Wave-particle duality means light behaves as both a wave and a stream of particles, depending on how you observe it. In experiments like interference and diffraction it acts like a wave, but in the photoelectric effect it acts like discrete particles (photons). Neither model alone is complete — you choose whichever one best describes the situation.
Problem 6
Answer and explanation
500000000000000 Hz
f = c ÷ λ = (3 × 10⁸) ÷ (6 × 10⁻⁷) = 0.5 × 10¹⁵ = 5 × 10¹⁴ Hz.
Problem 7
Hints
Keep powers of ten and length conversion consistent.
Answer and explanation
f=c/λ=1.0×10¹⁰ Hz.
Problem 8
Hints
State what the supplied observations or conditions establish, and separate that from any assumption.
Answer and explanation
Frequency stays constant across the boundary; speed and wavelength can change.
Problem 9
Answer and explanation
Photon energy, material interaction, absorbed amount and exposure conditions differ across situations.
The electromagnetic spectrum orders radiation by frequency or vacuum wavelength. Radio, microwave, infrared, visible, ultraviolet, X-ray and gamma labels cover ranges, not separate fundamental wave species. A material may transmit, reflect or absorb different ranges depending on its structure. Ionization removes an electron and requires enough interaction energy under the relevant conditions; heating and photochemical changes can occur through other mechanisms. Explain an application using energy, material response and dose rather than a color label alone.
Photon energy, material interaction, absorbed amount and exposure conditions differ across situations.
Response criteria
- Interpret labels, structures, axes, units and directions correctly.
- Explain the physical or environmental relationship or mechanism.
- Respect stated assumptions and distinguish observation from inference.
Problem 10
Answer and explanation
λ=4.00×10⁻⁷ m; f=7.50×10¹⁴ Hz and E=4.97×10⁻¹⁹ J per photon. This is not total beam energy without photon number.
λ=4.00×10⁻⁷ m; f=7.50×10¹⁴ Hz and E=4.97×10⁻¹⁹ J per photon.
This is not total beam energy without photon number.
Response criteria
- Use the stated measurements or conditions, with correct units.
- Connect the result to the physical or environmental mechanism or evidence relationship.
- Identify the assumption, model limit or further evidence requested.