Grade 10 Academic Science – Optics – (Physics)
Refraction
Science Perspectives 10 Section 12.1 Pages 515-519
Task

Do “Try This: Exploring with Light” on page 515.
Refraction is the bending of light when it travels from one medium to the next. Refraction occurs
because when light travels into a new medium, it changes speed. Light travels the fastest in the vacuum
(emptiness) of space. Light is the fastest thing in the universe traveling at approximately 300 000 km/s in
a vacuum.

Speed of light in a vacuum: c = 3.00  108 m/s
Light travels almost as fast in air so we use this value for the speed of light in air. Light travels
significantly slower in other media such as water and glass.
Rules for Refraction
1. The Incident Ray, Refracted Fay and Normal all lie in the same plane. The Incident Ray and the
Refracted Ray are on opposite sides of the “line” that separates the two media
2. a)
Light bends TOWARD THE NORMAL when it slows down in the second medium (i.e. the speed
of light in the second medium is less than the speed of light in the first media).
b)
Light bends AWAY FROM THE NORMAL when it speeds up in the second medium.
Partial Reflection and Refraction
When refraction occurs, some reflection always occurs also. This is called partial reflection and
refraction. The evidence for this is the fact that you can see through a glass window, but at the same
time you can also see a reflection.
Refraction
 Bending of light as it moves from one medium to another medium
 Bending of light at the boundary of two transparent substances
What causes Refraction?
Why does refraction occur? Look at the data about the speed of light in different materials and provide
your ideas.
Medium
Speed
(m/s)
Vacuum
3.00 X 108
Ice
229 X 108
Liquid Water
226 X 108
Glass
197 X 108
Note: The speed of light in a vacuum and the speed of light in air are only slightly different. The
difference is so small it is not significant (PROBLEM: What does that statement mean to you?)
Therefore, the same value is used for both a vacuum and air.
Rules for Refraction
 When a ray moves from a FAST
MEDIUM to a SLOW MEDIUM (see
illustration), the ANGLE OF
REFRACTION approaches the Normal
 When a ray travels from a SLOW
MEDIUM to a FAST MEDIUM, the
Refracted Ray moves away from the
Norm
 The Incident Ray and the Refracted Ray
are on the OPPOSITE SIDES of the
Boundary and the OPPOSITE SIDES of
the Normal.
When you see a straw refracted in water, you are looking at a VIRTUAL
IMAGE. Why?
Total Internal Reflection
When light rays travel from water (a slow medium) to
air (a fast medium), the rays bend (i.e., refract) AWAY
from the Normal.
Refraction of light waves in water. X represents the
actual position of a straw in water. Y represents the
apparent position of the pencil.
This occurs when the Angle of Refraction > the Angle
of Incident
What happens when the Angle of Refraction =
90O? In the diagram, this is “C” and it is called
the CRITICAL ANGLE.
When the Angle of Incident > Critical Angle,
there is TOTAL INTERNAL REFLECTION
(i.e., no transmission of light from the water).
The process is illustrated below.
How does light travel through an OPTIC CABLE? HINT: Total Internal Reflection
How does a diamond sparkle so much?
Partial Reflection and Refraction
Refraction is often accompanied by reflection. A reflection on water is a good example. This is Partial
Reflection and Refraction
HOMEWORK
 Questions 1-7 Page 519 Science Perspectives 10