Light
Images formed by a plane mirror
and curved mirror
The waves can pass through the object
The waves can be reflected off the object.
The waves can be scattered off the object.
The waves can be absorbed by the object.
The waves can be refracted through the object.
Difference between lens and mirror
• .
lens
Mirror
A lens focuses light
A mirror reflects light.
A lens is clear.
A mirror is reflective.
You can see through a lens
. You can’t see through a mirror
(typically, unless its a special kind).
focal point: The point at which rays or waves
meet after reflection or refraction, or the point
from which diverging rays or waves appear to
proceed.
focal length: The distance between the center
of a lens or curved mirror and its focus.
he distance from the vertex to the center of
curvature is known as the radius of curvature
Methods of Light Production
Methods of Light Production
 Incandescence:
 Production of light as a result of high temperature
 Ex: Candle, incandescent light bulb
glass bulb
tungsten filament
inert gas (argon)
Conducting wire
electrical contact
How does an incandescent light bulb work?
 The light bulb produces light when the fine coil of
tungsten (called a filament) is heated
 Temperature rises to ~2500°C when an electric current
passes through it!
 Tungsten is used because other metals at this high of a
temperature melts
 Incandescent lamps are very inefficient sources of light
because most energy is lost as heat
 Filled with a non-reactive gas because a more reactive gas
could combust
 Fluorescence:
 Immediate emission of visible light as a result of
absorption of ultraviolet light
 Ex: fluorescent lights
How does a fluorescent light bulb work?
1.
2.
3.
4.
5.
A long cylindrical glass tube is filled with mercury
vapour
Electrical current flows through the tube, from the
electrode which donates electrons to the electrode
which accepts electrons
As the current flows through the tube, it excites
atoms of mercury
The excited mercury atoms produce ultraviolet light
(which we cannot see)
The UV light strikes the fluorescent coating on the
inside of the glass tube and releases visible light
How does a fluorescent light bulb work?
Glass tubing
Electrical
contact
Electrode
(electron
donor )
Fluorescent coating
Electron
discharge
Mercury (Hg)
atoms
Electrode
Visible light produced
(electron
acceptor)
 Phosphorescence:
 Production of light by absorbing UV light and emitting
visible light over an extended period of time
 Ex: glow in the dark stickers which contain phosphors
Eclipses and its types?
QUIZ
White light shines on both papers. What color
will each paper appear to be?
Two lights are arranged above a white sheet of
paper. Determining the color that the sheet of
paper will appear in the diagrams below.
CHAPTER LIGHT Questions
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What is difference between lenses and mirrors?
Write the properties of light?
Draw diagram to show
i. reflection ii. Refraction
iii. Absorption
Iv. Convergent beam v. Divergent beam
vi. Transmission
Differentiate between convergent and divergent beam of light?
Differentiate between convex and concave mirror?
Explain the properties of images formed by convex, plane and concave
mirror?
• Explain the following term
• Radius, principle axis, vertex, focal point, focal length, center of curvature
• Explain the structure and function of pinhole
camera?
• Differentiate between real and virtual image?
• What are solar eclipse and it types? Explain by
diagram?
• Describe the methods of light production?