ENERGY

Energy is the ability to do work.

Moving, lifting, heating and lighting are examples of work.

We use energy to light our cities, heat our homes, move our cars, cook our food, play our music and give us pictures on television.

Energy from the Sun gives us light and heat.

When we eat, our bodies transform the energy stored in our food into energy to do work.

Everything we do is connected with energy in one form or another.

ENERGY SOURCES

There are two types of energy sources:

- Non-renewable energy sources cannot be replenished in a short period of time. These energy sources are fossil fuels, such as oil, coal and natural gas, and uranium.

- Renewable sources of energy can be replenished naturally in a short period of time. Traditional examples of these energy sources are sunlight, wind and water. There are some newer sources of renewable energy, such as biomass, which uses plants and other biological matter to produce energy.

ACTIVITY "ENERGY"

CLASSIFY THE FOLLOWING WORDS INTO TWO GROUPS: RENEWABLE AND NON-RENEWABLE ENERGY SOURCES.

Biomass, natural gas, sunlight, coal, oil, water, uranium, wind, fossil fuels.

TYPES OF ENERGY

- Electrical energy is the energy produced by the flow of electrical charge, such as the electricity used by washing machines and computers.

- Chemical energy is the energy produced by fossil fuels and biomass. In our bodies, it is the energy produced by the food we eat.

- Mechanical energy is the energy produced by things in motion, such as the wind.

- Thermal energy is the energy released as heat, from a stove, for example.

- Nuclear energy is the energy found in elements such as uranium and plutonium.

- Light energy is the energy found in light, such as the energy from the Sun.

ENERGY CONVERSION

One type of energy can be converted into another type of energy.

- In a fan, electrical energy is transformed into mechanical energy.

- At a nuclear power station, nuclear energy is transformed into electrical energy.

- In a light bulb, electrical energy is converted into light energy and thermal energy.

- In a car engine, chemical energy is trnsformed twice: into thermal energy ( the engine becomes warm) and into mechanical energy ( the car moves).

ACTIVITY " TYPES OF ENERGY"

MATCH THE TWO HALVES OF EACH SENTENCE

1. In a fan, electrical energy is
2. At a nuclear power statation, nuclear energy is
3. In a light bulb, electrical energy is
4. In a car engine, chemical energy is

a. transformed into thermal energy and mechanical energy.
b. transformed into mechanical energy.
c. transformed into electrical energy.
d. converted into light energy and thermal energy.

MAGNETS

A magnet is an object which can attract objects made of iron or mixtures of iron, such as steel. This attraction is called magnetism.

Magnets can be natural, such as the mineral magnetite, or artificial, such as magnets manufactured from metal.

Magnets have two poles: north and south. When the opposite poles of two magnets are placed together, the magnets attract each other. If the same poles are placed together, the magnets repel each other.

MAGNETIC FIELDS

Magnets create magnetic fields. They are the space around a magnet where materials, such as iron filings, are affected by magnetic forces.

ELECTROMAGNETS

An electromagnet is a conducting wire wrapped around a piece of iron, called a coil, which acts as a magnet when electrical current flows through it.

THE USES OF MAGNETS

Magnets are used in electric motors and generators for telephones, lights, televisors, computers and more.

- Magnetic recording media are used in audio cassettes, floppy disks and hard disks to store information in a very small space.

- Magnetic strips store information on credit cards.

- Electromagnets are used in televisions, computer monitors, loudspeakers and microphones.

ACTIVITY " MAGNETS AND MAGNETISM"

READ THE DEFINITIONS AND WRITE THE CORRESPONDING WORDS

1. An object which can attract other objects made of iron or mixtures of iron is called a .........
2. When the opposite poles of two magnets are placed together they..........
3. When the same poles of two magnets are placed together they.......
4. The area around a magnet affected by magnetic forces is called a ..............
5. A conducting wire wrapped around a piece of iron which acts as a magnet when an electrical current flows through the wire is called an .............

ELECTRICITY PRODUCTION

Electricity is produced at power stations or power plants.

Water, steam or wind moves a turbine connected to a generator. When the turbine rotates, the generator converts mechanical energy into electricity, using a magnetic field and a conductor.

Power stations use different energy sources to move the turbine. Some use non-renewable energies, such as coal, while others use renewable energies, such as wind.

ELECTRICITY TRANSMISSION

The electricity generated at a power station is transmitted through conducting wires to substations near populated areas. It is transmitted through tall towers and special electrical power lines called high-tension power transmission lines.

ELECTRICITY DISTRIBUTION AND CONSUMPTION

Power lines distribute electricity to homes, offices and industries. It is used by different appliances to produce:

- Heat: for example, radiators.
- Movement: for example, washing machines.
- Light: for example, computers.
- Sound: for example, doorbells.

ACTIVITY " ELECTRICITY"

COMPREHENSION: Answer these questions:

1. What moves a turbine?
2. What is the turbine connected to?
3. How do they work?
4. Where are substations located?
5. What is another name for the electrical power lines which transmit the electricity generated at a power station to substations?

ELECTRICAL CHARGES

There are two types of electrical charge: positive and negative. Negative charges can move from one place or object to another.

- If an object has more positive than negative charges, it is positively charged.

- If an object has more negative than positive charges, it is negatively charged.

- If an object has the same number of positive and negative charges, it is neutral.

Objects with opposite charges attract each other, and objects with the same charges repel each other.

If we rub an object with something made from a different material, we make electrical charges move, creating static electricity.

For example, if you rub a balloon onto your hair, negative charges move from your hair onto the balloon.Your hair becomes positively charged and the balloon becomes negatively charged. You can stick the balloon to your hair, and your hair stands on end.

ACTIVITY " ELECTRICITY"

Complete the sentences with the correct words.

1. There are ......... types of electrical charges.
2. Negative charges can............. from one place or object to another.
3. An object with the same number of positive and negative charges is..............
4. Objects with opposite charges................each other.
5. Objects with the same charges..................each other.

ELECTRICAL CURRENT

Electrical current is the flow of electrical charges. It transmits energy called electricity.

Electrical current flows differently, depending on the type of material through it flows.

- Conductors : electrical current flows easily through conductors. Most metals are conductors.

- Insulators: electrical current does not flow easily through insulators, such as air, glass, plastic, wood and rubber.

ELECTRIC CIRCUITS

An electric circuit consists of different components connected to each other to allow the flow of an electrical current.

The four basic components of an electric circuit are:

- A generator, which is the source of electricity, such as an electrical plant or a battery.

- An electrical component, such as a light bulb or a motor.

- Conducting wires.

- A switch to control the flow of electrical current. A switch in the on position closes the circuit and allows the flow of electrical current. A switch in the off position opens the circuit and breaks the flow of electrical current.

ACTIVITY "ELECTRICAL CURRENT"

TRUE OR FALSE? Decide if the sentences are true or false, and correct them if neccesary.

1. Electrical current flows easily through conductors.
2. Rubber is a conductor.
3. Electrical current does not flow easily through insulators.
4. Most metals are insulators.
5. An electric circuit has four basic components.
6. When the switch is on, it opens the electric circuit.