- Energy is the ability to do work.
Examples of energy are:
Light energy, Heat energy, Chemical energy, Mechanical energy, Sound energy
There are natural and artificial sources of light
Basic uses of Light
The process of glowing is known as bioluminescence
- Photosynthesis in plants
- Used in photography
- on roads, it is used for safety (traffic lights)
Properties of Light
i) Light travels in a straight line from the source
The experiment below shows how light travels in a straight line:
The diagram (a) above, the observer can see the candlelight through the holes made on the cardboards A, B and C.
When cardboard B is moved, the observer can no longer see the candlelight as before. Examine the figure below.
Also, looking through a rubber tube as shown below follows the same principle.
ii) Light travels in all directions.
For this experiment, consider a bulb.
Reflection of Light
- Reflection is the bouncing back of light on the surfaces of objects.
- There are two types of refection: Regular
and Irregular (Diffused)
reflection of light.
Characteristics of images on a plane mirror
- the image is virtual (not real)
- the distance between the object and the mirror is the same as the
distance between the mirror and the image.
- the image is upright
- the image is laterally inverted
A periscope uses the principle of refection to observe things around corners. The mirrors are placed at 45°. Observer the image below
Refraction of Light
Refraction is the bending of light waves as it moves from one medium to another e.g from air to water.
refers to the bending of light at the surface of water as it moves from air to water.
From the image above, the pencil appears broken. From the image below, the coin appears raised.
Attempt the experiments above to fully understand the effects of refraction of light.
Here are some effects of refraction of light
- A pool of water appears shallower
- A ruler appears broken when placed in water
- A coin in water appears raised
- Formation of a mirage (as seen on a road during shinny days)
The image below shows a road mirage. In a road mirage, there appears to be water on the road.
Dispersion of Light
Dispersion of light refers to the splitting of white light
into 7 different colours
The 7 colours form the spectrum. Can you name the 7 colours?
Try to remember the colours in order
Opaque, transparent and Translucent materials
materials allows light to pass through and you can see through them (e.g Air, Clear Glass, Clear water)
materials allows light to pass through but you cannot see through them clearly (e.g dirty water, oiled paper, plastics, frosted glass)
materials do not allow light to pass through them (e.g metal, stone, wood, iron sheet).
The sun is the main source of heat energy
Other sources include firewood, electricity, gas and more
The main uses of heat include warming, cooking, cooking, drying clothes and more.
The main effects of heat include
- Increase in body temperature
- enables the change in state of substance
- causes expansion
- permanent changes of some substances
Heat passes through solids, liquids and gases in different processes.
- this is the transfer of heat through solids
After sometime, the pin will fall. This is because, the heat is transferred from the point of heat on the metal to the rest of the metal rod. Once the heat reaches the waxed point, the wax will melt
and the pin will fall. Please note that when multiple pins are attached to the metal rod, the pin closest to the heat source will fall first.
- this is the process by which heat travels through liquids and gases.
To experiment heat transfer through air, place a piece of paper just above a heat source such as a candle. You will observe that the piece of paper
is carried upwards for sometime. This is because the hot air from the candle rises carrying the piece of paper with it as cold air drops.