Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
A light source is something that makes its own light. Examples include the Sun, stars, and a lit candle.
Darkness is the absence of light. If there is no light source, it is dark ().
Light travels from a source to our eyes, which allows us to see. If light is blocked or removed, we cannot see objects.
The Sun is a natural light source, while a torch or a lamp is an artificial (man-made) light source.
Reflectors are not light sources. Objects like mirrors and the Moon do not make their own light; they only reflect light from a source ().
It is dangerous to look directly at very bright light sources like the Sun, as they can damage our eyes.
📐Formulae
💡Examples
Problem 1:
Which of the following is a light source: a mirror, the Moon, or a firefly?
Solution:
A firefly.
Explanation:
A firefly creates its own light through a chemical reaction. A mirror and the Moon only reflect light from other sources (). Natural sources can be living organisms.
Problem 2:
Why can't you see your toys in a room where the curtains are closed and the lights are turned off at night?
Solution:
Because there is an absence of light ( lumens).
Explanation:
We need light to see. In a room with no light source, there is total darkness. Without light reflecting off the toys and entering our eyes, the toys remain invisible.
Problem 3:
Classify these as Natural or Artificial light sources: The Sun, a flashlight, and lightning.
Solution:
Natural: The Sun, Lightning. Artificial: Flashlight.
Explanation:
Natural sources occur in nature without human help. Artificial sources are made by humans and often require a battery or electricity to function.