(A)forms of energy
Energy can be defined as the capacity to perform work. Thus the unit of energy is the same as that of work, i.e., the SI unit of energy is the joule, j. In the world we live in, energy appears in various forms as mentioned earlier.
- Kinetic energy, such as the energy of a moving car or a falling stone .
- Chemical energy, such as the energy in our food which makes us grow.
- Heat energy, such as the energy developed in a steam engine, or a car.
- Electrical energy, such as the energy travelling through wires and used in driving our fans, running refrigerators and lightning houses.
- Light energy which enables us to see
- Sound energy such as that from loudspeakers
- Nuclear energy: energy from the nucleus of the atom
- Elastic energy: energy stored in a spring
(B)world energy resources
The word energy resources are of two types: renewable and non-renewable.
Examples of the renewable resources are:
- Solar energy: when it falls on solar cells, electricity is produced. Light also is important in the production of carbohydrates in green plants
- Wind: this turns the windmill, which produces electricity for work in the farm.
- Hydroelectricity: in dams, water turns generators and produces electricity e.g kainji dam. Other examples are tides and oceans.
Examples of non-renewable resources are:
- Petroleum: the gas is used in power stations to produce electricity, e.g a farm power station. The gas and kerosene are used to drive vehicles. Thus, chemical energy is transformed to mechanical energy.
- Coal: burning of coal produces much heat to boil water in turbines for driving trains and ships. Coal is used as fuel for cooking.
- Nuclear energy: this produces enormous heat to operate turbines and drive ships and aircrafts. With time, it will be put into more uses.
- Food eaten by man is broken down and energy released for human activities.
(C) conservation of energy
All forms of energy can be transformed from one form to another by means of suitable machines or apparatus. For example:
(I) the energy in the nuclei of atoms produces heat energy, which in turn can be used to generate electrical energy.
(II) solar energy (energy from the sun) can be collected, stored and transformed into various forms of useful energy.
(III) the mechanical energy that moves a car comes from heat energy derived from the burning of fuel, which is stored as chemical energy.
(IV) the telephone works on the principle of energy conversion from sound to electrical and back to sound.
(V) when brakes are applied to a moving car, the mechanical energy originally possessed by the car is not lost when the car stops, but is changed to heat in the brakes and tyres and some sound energy.
Note: the principle of conservation of energy states that although energy can be changed from one form to another,the total energy of a given system remains unchanged, i.e, energy can neither be created nor destroyed during a transformation.
1.which of the following best describes the energy changes which take place when a steam engine drives a generator which lights a lamp? (Jamb 1983)
A. Heat —- light —- sound —- kinetic
B. Kinetic—- light —- heat —- electricity
C. Heat —- kinetic —- electricity —- heat and light
D. Electricity —- kinetic —- heat —- light
E. Heat —- sound —- kinetic —- electricity
2. A Dynamo primarily converts (jamb 1988)
A. Mechanical energy into electrical energy
B. Electrical energy into kinetic energy
C. Potential energy into kinetic energy
D. Kinetic energy into potential energy
3. Which of the following correctly describes the energy changes in the generation of light by a hydroelectric power station? (Jamb 1993)
A. Electrical —- mechanical —- potential —- light
B. Potential —- mechanical —- electrical —- light
C. Mechanical —- sound —- electrical —- light
D. Kinetic —- mechanical —- electrical —- light
4. Electrical resistance is the property of an electrical conductor that causes electrical energy to be converted into(Wassce 1993)
A. Mechanical energy
B. Solar energy
C. Heat energy
D. Magnetic energy
E. Chemical energy
5. Electrical motor primarily converts( Wassce 1993)
A. Electrical energy into chemical energy
B. Electrical energy into heat energy
C. Kinetic energy into potential energy
D. Electrical energy into mechanical energy
E. Mechanical energy into light energy
6. Electrical energy supplied by leclanche cell is obtained from (wassce 1994)
A. Nuclear energy
B. Magnetic energy
C. Solar energy
D. Chemical energy
E. Mechanical energy
7. The main function of the mouthpiece of a telephone is to convert sound energy into ( Wassce 1996)
A. Heat energy
B. Light energy
C. Chemical energy
D. Electrical energy
E. Mechanical energy
8. State the energy transformation which occurs when a car is brought to rest by its brakes.
Answer: when brakes are applied to a moving car , the mechanical energy originally possessed by the car is not lost when the car stops, but is changed to heat in the brakes and tyres along with sound energy.