General
UNIT 7: Light and heat
In our environment, work can be done during day time or at night when there are other sources of light other than sunlight. Some sources of light can also give us heat.
The essential questions to be answered after this unit are:
• What are the various sources of light and heat?
• What is the importance and dangers of light and heat?
• What can I use to measure my body temperature and how?
Activity 1
1. Look at the pictures a, b, c, d, e and f;
2. Explain what you see in the pictures. What is the common characteristic of materials in pictures?
3. Identify sources of light you know.
What have you discovered from the pictures?
I have discovered that
• There is light and darkness.
• Major sources of light are: sun, torch, fire, candle, lanterns, Kerosene lanterns, bulbs, match stick, pressure lamp, fire wood…and others.
Activity 2
1. Look at the pictures a, b and c.
2. What separates the two parts observed in picture a?
3. Can a person in picture c search and get easily any material he /she is looking for in that room? Why?
4. Prepare a dark room by putting curtains on the windows and doors such that no light can enter. Explain what is darkness?
What have you discovered from the pictures?
I have discovered that
There is always darkness when there is no light.
Activity 3
1. Look at the pictures a, b and c;
2. What do the pictures show?
3. Why do the shadows in pictures a, b, and c have different height?
4. What is the role of the sun in the presence of the shadow?
5. Measure the height of the shadow for any tree in your school
compound at different time intervals (morning, afternoon and
evening). Give reasons why the tree’s shadow has a different height.
6. Using a torch, make a shadow of a notebook and pen in your
classroom. What do you think is a shadow?
What have you discovered from the pictures?
I have discovered that
A shadow is an image formed when light is blocked.
Activity 4
1. Look at the pictures (a and b);
2. What do the pictures and b show?
3. Find where there is fresh green grass in your school compound.
Find a big stone and cover some grass. Wait for seven days and then remove the stone.
What have you seen? Now, explain the importance of sunlight to plants.
What have you discovered from the pictures?
I have discovered that
• Light helps people to see.;
• Light allows plants to have green color.
• Light helps plants to make their own food (starch).
Activity 5
1. Look at the pictures a, b, c and d;
2. What do the pictures a, b, c and d show?
3. In the pictures a, b, c and d choose a picture which shows a pupil who is reading while avoiding the dangers of light.
Why have you chosen that picture?
4. What are the dangers of too much light or dim light?
What have you discovered from the pictures?
I have discovered that
• Too much light affects the eyes.
• Dim light also affects the eyes.
Ways of avoiding the dangers of light:
• We should avoid reading under too much light or dim light.
• We should use recommended sun glasses (sun gurgles) to reduce the amount of light.
Activity 6
1. Look at the pictures a, b, c, d, e and f;
2. What do the pictures a, b, c, d, e and f show?
3. Which of the materials shown in pictures a, b, c, d, e and f can produce heat?
4. Identify some of the materials you use at home that give out heat?
What have you discovered from the pictures?
I have discovered that
Sources of heat are: Sun, candle, lantern, kerosene lantern, electrical bulb, match stick, gas lamp, firewood and others.
Activity 7
1. Look at the pictures a, b, c and d;
2. Look at the picture a, b, c and d show?
3. Basing on Pictures a, b, c and d explain the importance of heat to livings things.
What have you discovered from the pictures?
I have discovered that
Heat is important because:
• Heat helps in cooking of food;
• Heat helps in warming the house;
• Heat helps in drying of clothes and crops
• Heat helps young animals to grow well (chicken).
• Heat helps in ironing of clothes
Activity 8
1. Look at the pictures (a and b);
2. What do the pictures a and b show?
3. What are the dangers of heat shown in the pictures a and b?
4. In which way can you protect yourself from the dangers of too much heat ?
What have you discovered from the pictures?
I have discovered that
Heat causes the following effects:
• Heat leads to loss of water in living things;
• Heat leads to burning of food when cooking;
• Heat leads to drying of plants and crops;
• Heat causes bush burning (it is easy for dry grass to catch fire).
Activity 9
1. Look at the pictures a, b, c and d;
2. What do the pictures a, b, c and d show?
3. What are the types of thermometers shown in the pictures a, b, c and d?
4. What are the parts that make up a thermometer ?
5. What is the use of a thermometer ?
What have you discovered from the pictures?
I have discovered that
There are three types of thermometers:
• Medical/clinical thermometer;
• Laboratory thermometer;
• Meteorological thermometer (Six’s thermometer) A thermometer has three major parts:
Capillary (Mercury or alcohol) tube, bulb and Stem.
The use of a thermometer is to measure the temperature of the human body, object or place.
Activity 10
1. Look at the pictures a, b, c and d;
2. What do the pictures a, b, c and d show?
3. Measure your body temperature following the steps below:
• Shake (calibrate) the thermometer until it reads 0;
• Place the thermometer under your armpit and wait for three (3) minutes;
• Remove the thermometer from your armpit and read the new number it is showing.
What have you discovered from the pictures?
I have discovered that
To measure human body temperature, you follow the steps below:
• Bringing back the thermometer reading to 0 (by shaking);
• Put the thermometer under armpit;
• Read the new thermometer reading number after 3 minutes.
NB: The normal human body temperature is 37OC
Activity 11
1. Look at the pictures a, b, c, d, e, f and g;
2. What do the pictures a, b, c, d, e, f and g show?
3. Which objects in the pictures a, b, c, d, e, f and g give both light and heat?
4. Do all the sources of light also give heat? Explain and give examples.
What have you discovered from the pictures?
I have discovered that
• Most of the light sources are also heat sources.
Examples: Sun, torch, fire, candle, lantern, petrol/oil lamp, gas lamp, electrical bulb, match stick, fire wood.
• However, there are some small insects (beetles/ fireflies/ lightning bugs) that give out light but don’t produce heat.
End of Unit Assessment 7
1. Identify five objects that give out light.
2. What is the difference between light and darkness?
3. Write True or False:
a) Shadow is lack of light.
b) All sources of light are also sources of heat.
c) Our eyes can be affected badly when we read from sunshine without eye protection tools.
d) The normal human body temperature is 40oc.
4. Give two dangers of heat to plants and animals. 5. Show how a medical thermometer is used?
6. List four objects/materials that give out light but don’t give out heat.