1. Current and Charge
Chapter 21

2. What is an Electric Current?
An Electric Current is a flow of Electric Charge.
The path around which an electric current flows is called a Circuit.

3. What are Three Effects of An Electric Current?
A Heating Effect
Heat is produced at every point in the circuit, but mostly in the bulb.
A Chemical Effect
A chemical reaction occurs in the beaker as the current flows through it.
A Magnetic Effect
The current creates a magnetic field around the wire. This causes the magnetic compass needle to deflect from its normal North–South position.

4. What is an Electrical Conductor?
An Electrical Conductor is a substance through which electric current can flow.
Name four electrical conductors.
Silver, Copper and Aluminium are metals commonly used as conductors.
Water, the Human Body and the Ground are also conductors.

5. What is an Electrical Insulator?
An Electrical Insulator is a substance through which electric current cannot flow.
Name four electrical insulators.
Glass, any Plastic, Rubber and Air are electrical insulators.

6. The Structure of the Atom.
All matter is made up of atoms.
Every atom has a central part, called the Nucleus, which contains particles called protons.
Particles called Electrons orbit in the space around the nucleus.
Electrons are attracted to the protons and are repelled by other electrons. Protons repel protons.

7. Positive and Negative Charge
The forces of attraction and repulsion between protons and electrons are called Electrostatic Forces.
Particles that exert electrostatic forces on each other are said to be Electrically Charged.
Electrons are said to be Negatively Charged.
Protons are said to be Positively Charged.

8. Electric Current in a Metal Conductor
An Electric Current in a Metal is a Flow of Electrons.

9. What is the SI Unit of Electric Charge?
The SI Unit of Electric Charge is the coulomb (C).
What is the relationship between Current and Charge?
The Current is the amount of charge passing per second.

10. A steady current I flows in a circuit for t seconds
A steady current I flows in a circuit for t seconds. How much charge Q, passes any point in the circuit in this time?
Charge gone past = Current x Time taken
Q = I t

11. What is the SI Unit of Electric Current?
The SI Unit of Electric Current is the ampere (A).
What is the relationship between the ampere and the coulomb?
1 ampere = 1 coulomb passing per second.

12. When an arrow is used to show the direction in which current is flowing in a metal conductor, the electrons flow in the opposite direction.

13. What is a Direct Current (d.c.)?
Direct Current is current that flows in one direction only.

14. Draw the circuit symbol for a battery.
Which side is the positive terminal?
The longer side (The left side in the diagram )

15. What is Alternating Current (a.c.)?
An electric current that reverses direction every so often it is called Alternating Current (a.c.).
Current that flows through a domestic light bulb when connected to the mains electricity supply reverses direction 100 times every second. It is therefore an alternating current.

16. The sum of the currents flowing into the junction O is equal to the sum of the currents leaving the junction.

17. Circuit (A) below is called a Series Circuit since there is only one path for the current to follow.
The same amount of charge passes any point in this circuit every second.
The current flowing out of the battery is the same size as the current flowing back into the battery.
In (B), each ammeter reads the same value.

18. Measuring Current with an Ammeter.
An Ammeter must be connected In Series with the part of the circuit in which the current to be measured is flowing.
To measure the current, the circuit must be broken and the ammeter must be inserted in series with the circuit.

19. The Current is the same at every point in a Series circuit
Each ammeter in the circuit reads the same value.

20. Current in Parallel Circuits
At B the current splits. Some goes through Path 1, some goes through Path 2.
The sum of the values on ammeters 2 and 3 is equal to the value on ammeter 1 (or ammeter 4), i.e. I = I1 + I2.
Path 1 and Path 2 are said to be In Parallel with each other.

22. Draw a diagram to show two filament lamps connected in series with a battery.
Draw a diagram to show two filament lamps connected in parallel with a battery.
What is the advantage of connecting the lamps in parallel?