Physics Form One Notes – Light
Full text version of Physics Form One Notes on Light, transcribed from the supplied source document. Source images are intentionally omitted; all recognized text from the topic pages is included below.
Full text: This page contains the complete recognized text for source pages 97-104. For the original PDF layout and illustrations, use the WhatsApp button below.
Sources of Light
The Concept of Light
Explain the concept of light
Light can carry both energy and information. It both is the way the sun delivers energy to the
world, making life possible, and it is a very important way that we learn about the world, through
our sense of sight.
Sources of Light
Identify sources of light
‘The sun is the natural source of light. On the other hand, torch, candle, kerosene lamp, electric
bulb, Florescent lamp, ete are some common examples of artificial sources of light, bodies which
give out light are called Luminous bodies
Difference between Luminous and Non-luminous Bodies
Distinguish luminous from non-luminous bodies
Non-luminous bodies are bodies which do not produce light, non-luminous bodies are seen
because they reflect light from luminous bodies in such a way that our eyes receive light from
travel in a straight line. Due to transmission of light, we are able to see.
Propagation and Transmission of Light
The Concept of Rays and Beam of Light
Explain the concept of rays and beam of light
A straight line showing a path of light is called a ray which is the direction of the path taken by
light. Rays of light are represented in diagrams by full straight line with arrow marking the
direction in which the light is travelling
A beam is a stream of light rays, and it is usually represented by a number of rays. Rays of light
can converge (converging rays) or they can diverge (diverging rays)
97
A ray of light
Parallel rays
Diverging rays
Converging rays
98
converging lens
[i]. tocat point (|
( —
\i : >
i H
ee
focal length
Verification that Light Rays Travel in Straight Line
Verify that light rays travels in straight line
Aim: To demonstrate the rectilinear propagation of light.
Materials and apparatus
1. The pieces of card board with a hole in each
2. Source of light, eg. a candle.
Procedures
1. Put the pieces of cardboard with the holes in a straight line
2. Arrange them to a distance of about 50cm apart.
3. Place a lighted candle at one end of cardboard A. observe the light from behind cardboard
c
4. Now displace any one of the pieces of cardboard, eg. Cardboard B.
99
r Px
(a [> jc >
|
i hy )
ght Travels in a Straight tine
Propagation of light in straight line.
Observations
When observing from card C, the candle can be seen, Displacing any one of cardboards, the
candle can no longer be seen as the holes are no longer in a straight line. This happens due to the
fact that light travels in a straight line.
Transparent, Translucent and Opaque Materials
Identify transparent, translucent and opaque materials
Objects can be grouped according to transmission of light through them, ie. The degree passage
of light as light rays falls on their surface
Opaque bodies
These are bodies which do not allow light to pass through them, ie. Stones, wood, concrete walls
and bodies.
Translucent bodies
These are bodies which allow small amount of light falling on them to pass through e.g oiled
paper, some plastic materials and tinted glass.
Transparent bodies
100
‘These are bodies which allow all light to pass through them, e.g glass, pure water and air. The
transmission of light through different bodies can be investigated by performing other
experiment.
Aim: To investigate transmission of light,
Materials
1. Sheet of paper
2. Sheet of glass
3. Tinted glass
4. Card board
5. Oil paper
Guiding questions
1. Which of the materials are opaque?
2. Which of the materials are transparent?”
Reflection of Light
The Concept of Reflection of Light
Explain the concept of reflection of light
Reflections are obtained from hard and highly polished surfaces such as mirrors and sheets of
glass than from rougher surfaces, when light falls on the surface at an inclined plane angle, it is
sent back into the air. This is also the case when light falls on all highly polished metals. If light
falls on a polished surface at an angle 90°, it is sent back into the air on the same path.
Difference between Regular and Irregular Reflection of Light
Distinguish regular from irregular reflection of light
Surface can be classified into two types:
101
1. Highly polished surfaces, examples are mirror, polished cooking utensil and silvered iron
sheets.
2. Rough surface, examples are unpolished wooden table, sheet of paper and cobblestone
road.
Application of the Laws of Reflection of Light
Apply the laws of reflection of light
Reflection is guided by some natural laws called “Laws of reflection” the Laws of reflection
state that:
1. The incident ray, the reflected ray, and the normal at the point of incidence all lies in the
same plane.
2. The angle of incidence is equal to the angle of reflection.
Image Formed by a Plane Mirror
Describe image formed by a plane mirror
A clear image is recognised as a result of reflection of the beam striking the highly polished
surfaces. This is called regular reflection
\\ Xx AL /
LX XX /
VAV AV AN
Regular reflection.
If mirrors were replaced by a piece of sheet of paper, there would be no image to be seen even as
a result of diffuse or irregular reflection, this is shown below.
102
\ \ #\ x a
\/ x \ J
» \
A, A \ i
.T\\
NX \ /
PAS YVAN_
Irregular or diffuse reflection,
Terms used in reflection
When light rays strike a surface (e.g a mirror) there are two rays of importance, namely Incident
and Reflected rays, see the figure below:
7 Normal
Incident ray Reflected ray
inedence | Angle of
So | flection
x
_———
Reflection of light rays.
+ MO is array of light falling on a mirror; itis called the incident ray.
+ OP isa ray of light leaving the mirror after reflection; it is called the reflected ray. Line
NO is perpendicular to the mirror , it is called the normal. ANGLE MON is called the angle of
incidence. (i) this is the angle between the incident ray and the normal , angle NOP is called the
angle of reflection (1). this is the angle between reflected ray and the normal.
103