Light and Optics
Light is a form of energy that travels in straight lines at very high speed. When light hits a surface, it can be reflected, refracted, or absorbed, depending on the material.
What You Need to Know
Key Concept Diagram
Light travels in straight lines (rectilinear propagation) at 300,000 km per second
Reflection: light bounces off a surface — the angle of incidence equals the angle of reflection
Refraction: light changes speed and direction when it passes from one medium to another (e.g. air to water)
Transparent materials let light through; translucent materials let some light through; opaque materials block light
Key Vocabulary
Reflection
The bouncing back of light when it hits a surface
Refraction
The bending of light as it passes from one medium to another at an angle
Transparent
Allowing light to pass through completely, so objects can be seen clearly
Opaque
Not allowing light to pass through; objects behind cannot be seen
Knowledge Check
Select the correct answer for each question. Click "Check Answer" to see if you are right.
Question 1
A ray of light hits a mirror at an angle of 30 degrees to the normal. At what angle does it reflect?
Question 2
Why does a straw appear to "bend" when placed in a glass of water?
Question 3
Which material is OPAQUE?
Key Concepts Summary
- ●Light travels in straight lines (rectilinear propagation) at 300,000 km per second
- ●Reflection: light bounces off a surface — the angle of incidence equals the angle of reflection
- ●Refraction: light changes speed and direction when it passes from one medium to another (e.g. air to water)
- ●Transparent materials let light through; translucent materials let some light through; opaque materials block light