Optical Phenomena & Atomic Spectra is one of 10 topics in the Grade 12 Physical Sciences CAPS syllabus, covered across 3 lessons on Study Vault. Below are real practice questions from this topic with full worked answers.
Sample practice questions
Easy
1. The photoelectric effect is the emission of electrons from a metal surface when:
Light of a sufficiently high frequency shines on the metal
The metal is heated to a very high temperature
An electric current flows through the metal
The metal is placed in a strong magnetic field
Answer: Light of a sufficiently high frequency shines on the metal — The photoelectric effect specifically refers to electrons being ejected from a metal surface by incident light of sufficiently high frequency (above the metal's threshold frequency).
Easy
2. What name is given to a discrete "packet" or quantum of light energy?
A photon
An electron
A proton
A neutron
Answer: A photon — Light is modelled as being made up of discrete energy packets called photons, each with energy E=hf.
Medium
3. Light with a frequency below a metal's threshold frequency f0 shines on the metal. What is observed, no matter how bright (intense) the light is made?
No electrons are emitted at all
Electrons are emitted, but slowly
Electrons are emitted only in bright light
The metal melts
Answer: No electrons are emitted at all — Below the threshold frequency, no single photon carries enough energy to free an electron, so no photoelectrons are emitted regardless of intensity -- this is a key piece of evidence for the particle (photon) model of light.
