Charge (Oxford AQA IGCSE Physics)
Revision Note
Charge
Charge is a property of matter
Charge is measured in units called coulombs, C
Objects can be positively charged, negatively charged or neutral (i.e. not charged)
Objects are neutral if the positive charge and negative charge cancel each other out
For example, a neutral atom has an equal number of protons (positively charged particles) and electrons (negatively charged particles
If a neutral object gains electrons, it becomes negatively charged
If a neutral object loses electrons, it becomes positively charged
When two charged objects are brought close together, there will be a force of attraction or repulsion between those objects
Positive and negative charges
Remember:
Opposite charges attract
Like charges repel
In some objects, the electrical charges can move easily around the object
For example, in metals such as copper, electrons can move easily around the metal
Potential difference
For an electrical charge to flow through a closed circuit, it must include a source of potential difference (p.d.)
This is often called voltage or e.m.f.
Sources of potential difference include:
A cell
Batteries (multiple cells)
Electrical generator
The terminals in a cell make one end of the circuit positive and the other negative
This sets up a potential difference across the circuit
The symbol for the potential difference is V
In a closed circuit with a source of potential difference, electrons flow through the metal wire from the negative end to the positive end
The flow of electrons
The potential difference across a component in a circuit is defined as
The energy transferred per unit charge flowing from one point to another
For more information, read our revision notes about Voltage & Potential Difference
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