Download Physical Science 20 Notes Unit 1 Part 2B

2. Reflection of Light
When light is reflected off a surface the type of reflection depends on the
smoothness of the surface. Regular reflection occurs when reflecting
bodies are smooth such as a mirror, diffuse reflection occurs when the
reflecting surface is light in colour but irregularly shaped and reflex
reflection occurs when light is reflected from a manufactured surface such
as traffic signs.
Investigation #8 – Reflection in a Plane Mirror
Normal line
The following diagram represents how the
lines and angles of incidence are related
to the lines and angles of reflection.
angle of
incidence
angle of
reflection
Reflecting surface
Laws of Reflection
1. The angle of incidence is equal to the angle of reflection
2. The incident ray, the reflected ray and the normal to the reflecting
surface lie in the same plane.
If parallel beams of light fall on a polished surface, parallel beams are
produced (regular diffusion). Obeying the law of reflection, that the angle of
incidence = the angle of reflection, the parallel incident beams will produce
parallel reflected beams. On the other hand if the beams of light fall on a
rough surface (diffuse reflection) the rays have different angles of
incidences and therefore travel in different directions. The diagrams below
show both regular and diffuse reflection.
a. Images in a Plane Mirror
When you look into a mirror, you see an image of your face apparently
located behind the mirror. If you move towards the mirror, your image will
move closer to the mirror so that your image is always the same distance
from the mirror as the object. If you raise your right hand the image on the
mirror appears to be a left hand coming up to meet your right hand. Letters
viewed in a plane mirror appear reversed horizontally but not vertically. This
is called lateral inversion. The diagram below shows an example of lateral
inversion.
b. Applications of Plane Mirrors
Plane mirrors have many applications one of which is a looking glass i.e.
mirror. Other applications are:
a) Cameras – Plane mirrors are used in the viewfinders of single lens
reflex cameras (SLR’s). A mirror is hinged behind the lens of the
camera. When the shutter is released, the mirror flips out of the way to
let light fall on the film. As soon as the picture is taken the mirror flips
back to the original position.
b) Periscope – Used in submarines and created by using two plane
mirrors facing each other.
Assignment: Create a periscope using two plane mirrors and a piece of
cardboard.
c) Shooting Gallery – Bouncing light off of a mirror and hitting a target.
d) Optical Lever – When a plane mirror turns through a certain angle and
produces an image that turns through double the angle.
e) Kaleidoscope – Two plane mirrors are arranged at 60° in a hollow
tube. One end of the tube has an eyepiece and the other end coloured
pieces of glass. As you turn the glass a variety of patterns are created.
f) See-through Mirrors – Most mirrors made from glass have a
reflective layer of silver. This layer is protected with an opaque
coating. In see-through mirrors this coating is transparent.
g) Theatrical Effects – Produces an illusion of a ghost.
h) Right Angle Images – Produce three images.
Turn in Assignment #3