1. Grade 11 Physical Science – Mrs KL Faling
WAVES
Grade 11 Physical Science – Mrs KL Faling

2. GEOMETRICAL OPTICS

3. Light on an object:
The light can be transmitted
The light can be reflected
The light can be absorbed

4. REFLECTION
When a surface is shiny and smooth light is reflected

6. Terminology Normal Incident ray Reflected ray Angle of incidence
Angle of reflection
Hand out definition list

7. THE LAWS OF REFLECTION
The incident ray, the reflected ray and the normal must all be in the same plane
The angle of incidence is equal to the angle of reflection

8. EXAMPLE
Complete EX 9

11. The speed of light
The speed of light is constant in a specific medium.
If the medium changes so will the speed of light
The speed of light in a vacuum is 3 x 108 m·s-1
This is the maximum value for the speed of light
Light travels slower as the density of the medium increases.

12. REFRACTION

13. Refraction is the bending of light as it moves from one medium to another medium with a different optical density

14. Optical density is the measure of the speed of light or other electromagnetic waves through a medium

16. The light moves from an optically less dense medium (air) to an optically more dense medium (glass). The ray bends towards the normal.
When it leaves the block it moves from more dense to less dense and bends away from the normal.

17. REFRACTIVE INDEX
The refractive index is the ratio of the speed of light in air to the speed of light through another medium
Refractive index – Ratio it has no unit!
n = c / v

21. EX 10

36. Greater refractive index Slower speed of light in the medium
Greater optical density
INVERSELY PROPORTIONAL
INVERSELY PROPORTIONAL

37. Greater refractive index Greater optical density
DIRECTLY PROPORTIONAL

38. NOTE!!!!
Refraction is due to a change in speed of a wave as it enters different media!
THE FREQUENCY OF THE WAVE HOWEVER REMAINS CONTANT!

39. Snell’s law ni Sin(∂i) = nr Sin(∂r),
Dutch physicist Willebord Snell (1591 – 1626) derived the relationship between the different angles of light as it passed from one medium to another.
ni Sin(∂i) = nr Sin(∂r),
where: ni is the refractive index of the medium the light is leaving, ∂i is the incident angle between the light ray and the normal to the medium to medium interface, nr is the refractive index of the medium the light is entering, ∂r is the refractive angle between the light ray and the normal to the medium to medium interface.

40. SNELL’S LAW

41. EXAMPLES
1. Light travels from a medium with n = 1.25 into a medium of n = 1.34, at an angle of 27° from the normal to the interface of the two media. 
1.1 Will the speed of the light increase, decrease, or remain the same? 
1.2 Will the light bend toward the normal, away from the normal, or not at all?
1.3 What is the angle of refraction?

42. 2. Light travels from a medium with n = 1. 63 into a medium of n = 1
2. Light travels from a medium with n = 1.63 into a medium of n = 1.42, along the normal to the interface of the two media. 
2.1 Will the speed of the light increase, decrease, or remain the same? 
2.2 Will the light bend toward the normal, away from the normal, or not at all?
2.3 What is the angle of refraction?

43. COMPLETE EX 11

51. CRITICAL ANGLES
The critical angle is the angle of incidence where the angle of refraction is 90°.
The light must travel from an optically more dense medium to an optically less dense medium

52. Using SNELLS LAW TO DETERMINE THE CRITICLE ANGLE
EXAMPLE
Critical angle

53. If the angle of incidence is bigger than the critical angle, the refracted ray will not emerge from the medium, but will be reflected back into the medium.
This is called TOTAL INTERNAL REFLECTION

55. The conditions for T.I.R are:
Light must travel from an optically denser medium to an optically less denser medium.
The angle of incidence must be greater than the critical angle.

56. NOTE:
Each pair of media have their own unique critical angle.
For example glass to air is 42° and water to air is °