Units Used In This Topic:

## Current, Potential Difference & Resistance

Circuit symbols are used to make sure everyone understands the diagram clearly and to avoid mistakes being made.

The symbols you need to be able to draw and name are:

For electrical charge to flow through a closed circuit the circuit must include a source of potential difference, measured in Volts. Charge is measured in Coulombs.

Electric current is a flow of electrical charge. Current is measured in Amps.

The size of the electric current is the rate of flow of electrical charge.

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Charge flow, current and time are linked by the equation:

charge flow = current × time

Question:A lithium-ion battery is put on charge for 1800 s
The current is 40 A
Calculate the total charge flow during this time.

Question:Calculate the charge flow when there is a current of 0.50 A in the wire for 17 s

A current has the same value at any point in a single closed loop.

Resistance is measured Ohms.

The Potential Difference is the energy transferred to/from each unit of Charge.

Unit: Volt (1 Volt = 1 Joule/Coulomb)

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The current (I) through a component depends on both the resistance (R) of the component and the potential difference (V) across the component.

The greater the resistance of the component the smaller the current for a given potential difference (pd) across the component.

Current, potential difference or resistance can be calculated using the equation:

potential difference = current × resistance

Question: The resistance of a 24 W, 12 V filament lamp depends on the current flowing through the lamp. For currents up to 0.8 A, the resistance has a constant value of 2.5 Ω.
Calculate the potential difference across the lamp when a current of 0.8 A flows through the lamp.

Question:Calculate the resistance of a lamp when the potential difference across the lamp is 3.3 V the current is 0.15 A.