Static Electricity Reading

Charge and static
All matter has , in the same way that all matter has mass. Atoms have overall charge – they are . This is because atoms contain equal numbers of and . Electrons carry a electric charge and protons carry a electric charge.

Static
can be made to move from one object to another. However, do not move because they are tightly bound in the nuclei of atoms.
For example, when a plastic rod is rubbed with a duster, are transferred from one material to the other. The material that gains electrons becomes charged. The material that loses electrons becomes charged.

Static charge occurs when electrons build up on an object. Static charge:

can only build up on objects which are , eg plastic or wood
cannot build up on objects that act as , eg metals
Conductors allow the electrons to flow away, forming an .
When a static charge on an object is , an electric current flows through the air. This can cause . is an example of a large amount of static charge being discharged.

Opposite (unlike) charges one another. Like charges one another.

Demonstrating charge
The only way to tell if an object is charged is to see if it another charged object. This is because a charged object can attract an insulator.

For example, a charged plastic object such as a comb or ruler repels electrons in a piece of paper. The near side of the paper to the plastic object becomes charged, so it is to the plastic object. This is why party balloons hair after they have been rubbed on a shirt or jumper.

Current
Current is the of of . In metal wires, electrons move and cause a . The following conditions are needed for an electric current to flow:
1. a source of potential difference, such as a , or
2. a closed , which provides a complete path for the charges to move through

Originally, current was defined as the flow of charges from positive to negative. Scientists later discovered that current is actually the flow of electrons, from to . The original definition is now referred to as ‘conventional current’, to avoid confusion with the newer definition of current.

Calculating current
To calculate current, use the equation:
-charge flow = ×

This is when:
1. charge flow is measured in (C)
2. current is measured in (amps) (A)
3. time is measured in (s)
Each electron in a circuit carries a very small charge but there are many of present. Many everyday currents for small household appliances will be measured in milliamps, mA: 1,000 mA = 1 A.
Example calculation
A current of 60 mA flows through a lamp for half an hour. Calculate the charge transferred.
---- 60 mA = 60 ÷ 1,000 = A
---- 0.5 hours = minutes
---- 30 × 60 = s

charge flow = current × time
= 0.060 × 1,800
= C

Question
A charge of 5.0 C is transferred through a wire in 20 s. Calculate the current that flows in the wire.
Current= Charge Flow/ Time
Current= C/ s
Current= A