Potential difference and resistance
Potential difference
The current through a component depends on both the The opposition in an electrical component to the movement of electrical charge through it. Resistance is measured in ohms. of the Parts of an electrical circuit, eg resistors, lamps, motors etc. and the The potential difference (or voltage) of a supply is a measure of the energy given to the charge carriers in a circuit. Units = volts (V). This is the voltage between two points that makes an electric current flow between them. across the component.
Measuring potential difference
To measure the potential difference across a component, a A device used to measure potential difference or voltage. must be placed In a parallel circuit, the current divides into two or more paths before recombining to complete the circuit. Lamps and other components in these different paths are said to be in parallel. with that component in order to measure the difference in energy from one side of the component to the other. Potential difference is also known as The potential difference across a cell, electrical supply or electrical component. It is measured in volts (V). and is measured in volts (V).
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Energy, voltage and charge
When a charge moves through a potential difference, electrical Energy transferred by a force. Work done = force × distance moved in the direction of the force. is done and energy transferred. The energy transferred can be calculated using the equation:
Energy transferred = charge moved × potential difference
\(E = Q \times V\)
This is when:
- potential difference (V) is measured in volts (V)
- energy (E) is measured in joules (J)
- charge (Q) is measured in coulombs (C)
One volt is the potential difference when one coulomb of charge transfers one joule of energy.
Example
What is the potential difference between two points if 2 C of charge shifts 4 J?
\(V = \frac{E}{Q} \)
\(V = \frac{4}{2} \)
\(V = 2 \ V \)
Question
How much energy is transferred when 3 C of charge moves through a potential difference of 6 V?
\(E = V \times Q\)
\(E = 6 \times 3\)
\(E = 18 \ J\)
Resistance
When a charge moves through a potential difference, electrical Energy transferred by a force. Work done = force × distance moved in the direction of the force. is done and energy transferred. The potential difference can be calculated using the equation:
potential difference = current × resistance
\(V = I \times R\)
This is when:
- potential difference (V) is measured in volts (V)
- current (I) is measured in amps (A)
- resistance (R) is measured in ohms (Ω)
From the equation, it can be seen that increasing the resistance for a certain potential difference will reduce the current passing through. For example, if a variable resistor is adjusted to double its initial resistance, the current passing will be halved.
Example
What is the potential difference if a current of 2 A flows through a resistance of 40 Ω?
\(V = I \times R\)
\(V = 2 \times 40\)
\(V = 80 \ V\)
Question
What is the resistance of a component if 12 V causes a current of 2 A through it?
\(V = I \times R\)
\(R = \frac{V}{I}\)
\(R = \frac{12}{2}\)
\(R = 6 \ Ω\)
