Light: Reflection and Refraction
Light is a form of electromagnetic radiation that travels in straight lines at 300,000 km/s in a vacuum. When light hits a surface it can be reflected, and when it passes from one medium to another it bends (refracts).
What You Need to Know
Key Concept Diagram
Light travels in straight lines called rays; it can be reflected, refracted, or absorbed
Law of Reflection: angle of incidence = angle of reflection (both measured from the normal)
Refraction: light bends when it passes from one medium to another due to a change in speed
Light slows down in denser media; it bends toward the normal when slowing and away when speeding up
Total internal reflection occurs when light tries to move from a dense to less dense medium at an angle greater than the critical angle
Key Vocabulary
Reflection
Light bouncing back from a surface; the angle of incidence equals the angle of reflection
Refraction
The bending of light as it passes from one medium to another due to a change in speed
Normal
An imaginary line perpendicular (at 90 degrees) to a surface; angles of reflection and incidence are measured from it
Critical Angle
The angle of incidence above which total internal reflection occurs when light moves from a denser to a less dense medium
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 incidence of 35 degrees. What is the angle of reflection?
Question 2
Why does a straw appear to be bent when placed in a glass of water?
Question 3
Which technology uses total internal reflection to transmit data as light signals?
Key Concepts Summary
- ●Light travels in straight lines called rays; it can be reflected, refracted, or absorbed
- ●Law of Reflection: angle of incidence = angle of reflection (both measured from the normal)
- ●Refraction: light bends when it passes from one medium to another due to a change in speed
- ●Light slows down in denser media; it bends toward the normal when slowing and away when speeding up
- ●Total internal reflection occurs when light tries to move from a dense to less dense medium at an angle greater than the critical angle