Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Light is a form of energy that allows us to see the world around us. It travels in straight lines called rays, which can be represented by the symbol .
A light source is an object that makes its own light. Natural sources include the Sun and stars, while artificial sources include lightbulbs and torches.
Darkness is the complete absence of light. We cannot see anything in total darkness because there is no light to enter our eyes.
Reflection occurs when light hits a surface and bounces off it. Smooth, shiny surfaces like mirrors reflect light very well, allowing us to see an image.
Non-luminous objects, such as the Moon or a chair, do not produce their own light. We see them because light from a source reflects off them and enters our eyes.
Opaque materials block all light, creating a shadow. The shadow's shape is similar to the object because light travels in straight lines and cannot curve around it.
The speed of light in a vacuum is approximately , which is the fastest speed in the universe.
📐Formulae
💡Examples
Problem 1:
If a light ray hits a flat mirror at an angle of incidence of , what will be the angle of reflection?
Solution:
Explanation:
According to the Law of Reflection, the angle of incidence is always equal to the angle of reflection . Therefore, if , then .
Problem 2:
The Sun is approximately away from Earth. If light travels at , how long does it take for sunlight to reach us?
Solution:
(or about minutes and seconds)
Explanation:
Using the formula , we calculate .
Problem 3:
Is the Moon a light source? Explain why we can see it at night.
Solution:
No, the Moon is not a light source.
Explanation:
The Moon is a non-luminous object. We see it because it reflects the light from the Sun ().