Electricity

Sources of electrical energy

1. Electrical energy is energy produced when electric current flows.
2. A source of electrical energy is any device that produces electric charges or electric current.

Electric current

1. Moving electric charges (electrons) produce electric current.
2. Electric current is produced when electrons flow in a certain direction in a conductor.
3. Electric current is the rate of the flow of negative charges or electrons through a conductor.
4. The Van de Graaff generator is a device that can produce electric charges (electrostatic charges) of very high voltage on its dome.

Voltage

1. Voltage is electrical energy that is needed to enable electrons to flow from one point to another in a conductor.
2. Voltage produces force that pushes electrons through a circuit to produce electric current.

Resistance

1. The characteristic of a material that opposes the flow of electrons or electrical charges is called resistance.
2. A material with high resistance allows only a small current to pass through it.
3. Resistance in a conductor, for example a wire, depends on
   length of conductor
   The longer the conductor, the higher its resistance.
   diameter or thickness of conductor
   The bigger the diameter of the conductor, the lower its resistance.
   type of conductor
   Different types of conductor have different resistance.
   Copper and aluminium which are widely used as electric wires are a few metals that have low resistance.
4. Some conductors have high resistance to current that flows through them. This type of conductor is called a resistor.
5. The following laboratory activities are carried out to study the effects of length, thickness, and type of conductor on their resistance.

Direction of electron flow and current in an electric circuit

1. In a dry cell, current is produced when electrons flow from the negative terminal of the cell to the positive terminal through a wire.
2. However, the direction of current flow is the opposite of the direction of electron flow.
3. Electric current flows from the positive terminal to the negative terminal of a cell.

Measuring Electricity

Measuring electric current

1. Electric current that flows from a source of electrical energy can be measured with an ammeter.
2. The unit of measurement for current is ampere (A).
3. The ammeter is connected in series to a circuit when measuring current.
4. The positive terminal of the ammeter should be connected to the positive terminal of the

Measuring voltage

1. Voltage can be measured with a voltmeter.
2. The unit of measurement for voltage is volt (V).
3. The voltmeter is connected in parallel to a circuit when measuring voltage.
4. The positive terminal of the voltmeter should be connected to the positive terminal of the electric source in an electric circuit.

Measuring resistance

1. Resistance is measured in the unit of ohm.
2. The symbol of ohm is S2.
3. A resistor is a device that is used to reduce the electric current that flows in a circuit.
4. The bigger the ohm value in a resistor, the bigger is its resistance.