1. How is heat generated?
The Universe is made up of matter and energy. Matter is made up of atoms & molecules. Energy causes the atoms & molecules to always be in motion - either bumping into each other or vibrating back and forth.
The motion of atoms and molecules creates a form of energy called heat or thermal energy which is present in all matter.

2.  It is the total energy of molecular motion in a substance.
What is heat?
 It is a form of energy transferred from one body to another body because of a temperature difference between bodies.
 It is the total energy of molecular motion in a substance.
Examples of Heat transfer
a. If you touch a hot stove, heat energy enters your hand ( thus you feel hurt ) because the stove is warmer than your hand.
b. If you touch a piece of ice, energy passes out of your hand and into the colder ice thus the ice melts.

3. What are the sources of Heat?
 The Sun
Most of our heat may be traced from the sun.
 Earth’s Interior
The earth’s interior is hotter than its surface.

4. Sources of Heat
 Chemical Action
Our food are cooked by the heat of burning wood or by LPG.
The oxygen we breathe burns the food we eat.
We get heat energy from the food we eat.

5. Sources of Heat Machines can be sources of heat  Mechanical energy
Infrared image of a hair dryer
Infrared image of light bulb
 Electrical Energy

6.  Nuclear Energy
Radioactive substances give off heat.
 Friction
When you rub your hands.
When you use the brakes on your car.

7. What are the effects of Heat?
 Change in temperature
Heating water in the kettle
Excessive heat in a feverish child

8. What are the effects of Heat?
 Phase change
Melting/Fusion – “heat releasing process”
Vaporization – “heat absorbing process”
Evaporation – “Cooling process”
Condensation – “Warming process”
 Expansion
Change in Length or dimension
Change in Volume

9. Amount of Heat (Q) to change the temperature
Q = mct
Where Q – heat to change temperature
c – specific heat (constant)
 t – change in temperature
 t is in C
c is in j/Kg C
m is in kg
Unit of heat: joules ( j ), calorie (cal) , British Thermal Unit ( BTU )

10. Specific Heat ( j/KgC )
Specific heat ( c ) of selected substances
Substance
Specific Heat ( j/KgC )
Aluminum
900
Silver
230
Water
4186
Zinc
388
Copper
390
Ice
2060
Lead
128
Iron
450
Steam
2020
Glass
837

11. Heat to change temperature
Example 1: An 80-kg man has a fever of 2 C above the normal. Assuming that the human body is mostly water, how much heat must be removed from the body to eliminate the fever?
Example 2:What is the heat required to raise the temperature of 0.5kg of ice from 0 C to 5 C?

12. Heat to change temperature
Example 3: A 50g sample of copper is initially at 25 C. If 1200 joules of heat is added to the copper, then what is its final temperature?
Example 4: A certain substance was heated from 50 C to 80 C. If 200joules of heat has been added to the substance that is 30g then what is its specific heat?

13. EXERCISE :Heat
1. A 80g piece of zinc is 35C. If 400joules of heat is added then what is its
final temperature?
2. A certain substance was heated from 65 C to 90 C. If 110joules of heat has been added to the substance that is 50g then what is its specific heat?
3. How many joules of energy is required to raise the temperature of 300g of
lead from 45 C to 120 C?
4. How many joules of energy is required to raise the temperature of 100g of
iron from 20 C to 100 C?
5. A 50g piece of Aluminum is at 20 C. If 400joules of heat is added then what is its
6. A certain substance was heated from 65 C to 90 C. If 150joules of heat has been added to the substance that is 50g then what is its specific heat?