Electrical charge and current
There are two types of Moving electric charges, eg electrons moving through a metal wire. - direct and alternating. In a Direct current is the movement of charge through a conductor in one direction only., the flow of Subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons. is consistently in one direction around the circuit, in an Also called ac. An electric current that regularly changes its direction and size., the direction of electron flow continually reverses.
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Charge
Electrons are negatively Property of matter that causes a force when near another charge. Charge comes in two forms, positive and negative. For example, a negative charge causes a repulsive force on a neighbouring negative charge. particles and they transfer energy through wires as electricity.
Charge is a property of a body which experiences a force in an electric field. Charge is measured in coulombs (C).
Since electrons are so small and one electron will not have much of an effect anywhere, it is more useful to refer to large groups of electrons. One coulomb of charge is equivalent to 6,250,000,000,000,000,000 electrons.
Current
In a closed circuit that includes a source of potential difference (voltage) there will be a current flowing around the circuit.
When current flows, electrical Energy transferred by a force. Work done = force × distance moved in the direction of the force. is done and energy transferred. The amount of charge passing a point in the circuit can be calculated using the equation:
charge = current × time
\(Q = I \times t\)
This is when:
- charge (Q) is measured in coulombs (C)
- current (I) is measured in amperes (A)
- time (t) is measured in seconds (s)
One ampere is the current that flows when one coulomb of charge passes a point in a circuit in one second.
Example
A current of 1.5 amps (A) flows through a simple electrical circuit.
How many coulombs of charge flow through a point in 60 seconds?
\(Q = I \times t\)
\(Q = 1.5 \times 60\)
\(Q = 90 \ C\)
Question
How much charge has moved if a current of 13 A flows for 10 s?
\(Q = I \times t\)
\(Q = 13 \times 10\)
\(Q = 130 \ C\)
Question
How much current flows when 10 C passes down a wire in 2 s?
\(Q = I \times t\)
\(I = \frac{Q}{T}\)
\(I = \frac{10}{2}\)
\(I = 5 \: A\)
Measuring current
Current is measured using an A device used to measure electric current.. To measure the current through a component, the ammeter must be placed in A circuit where one component follows directly from another, eg three bulbs in a row with no junctions are said to be connected in series. with that component.