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Potential difference (V) is the energy transferred per unit charge between two points in a circuit, measured in volts (V). Free GCSE Physics notes.
Current, Potential Difference and Resistance is part of Current, potential difference and resistance in GCSE AQA Higher Physics.
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Potential difference (V) is the energy transferred per unit charge between two points in a circuit, measured in volts (V). Free GCSE Physics notes.
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Use this lesson to stay inside Current, potential difference and resistance while connecting the detail back to the wider Electricity topic.
Read the core explanations from Current, Potential Difference and Resistance before testing yourself from memory.
Why does a torch dim when the batteries run low? Why do phone chargers get warm? The answer lies in understanding three fundamental electrical quantities that control every circuit around you.
These three quantities are connected by the most important relationship in electronics. When Georg Ohm discovered this pattern in 1827, he unlocked the key to understanding all electrical circuits.
The beauty of Ohm's Law is that you can rearrange it to find any quantity if you know the other two. This triangle method helps you remember:
Here's the crucial insight: current depends on both voltage AND resistance. Double the voltage and current doubles. Double the resistance and current halves. This is why your phone charges slowly through a long cable - the extra wire length adds resistance.
Ever wondered why power lines use thick cables over long distances? The answer lies in how resistance changes with wire length. This relationship affects everything from your headphone cables to the National Grid.
At constant temperature, resistance is directly proportional to wire length. Double the length, double the resistance. This happens because electrons have to travel further and collide with more ions in the metal lattice along the way, so there are more opportunities for energy to be transferred.
The relationship is: longer wire → more collisions → higher resistance → lower current (for the same voltage). This is why:Extension leads reduce the power to your devicesPhone chargers work better when shortPower companies use high voltages for long-distance transmission
Exam questions love testing Ohm's Law calculations. Here's the foolproof method that gets you full marks every time. Notice how examiners award marks for method, substitution, and final answer.
Worked example: Finding Current Using Ohm's Law
A 12V battery is connected to a 4Ω resistor. Calculate the current flowing through the resistor. [3 marks]
Answer: Current = 3A
Worked example: Finding Resistance from Current and Voltage
A component has 6V across it and 0.5A flowing through it. Calculate its resistance. [3 marks]
Answer: Resistance = 12Ω
Ohm's Law questions appear in every GCSE physics exam. Students often know the formula but lose marks on technique. Here's how to avoid the common traps and secure full marks.
A common misconception is that current gets used up as it flows around a circuit. This is wrong. In a series circuit the current is the same at all points, while the potential difference is shared across the components. For an ohmic conductor at constant temperature, a bigger potential difference gives a bigger current because V = IR.
Mark scheme language: When explaining why current decreases as resistance increases, use the phrase 'inversely proportional' or 'inversely related'. This shows you understand the mathematical relationship and often secures the explanation mark.
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
Potential difference (V) is the energy transferred per unit charge between two points in a circuit, measured in volts (V). It is also called voltage.
Ohm's Law connects potential difference, current and resistance: V = IR. Double the voltage and the current doubles; double the resistance and the current halves, so current is inversely proportional to resistance for the same voltage.
The Ohm's law triangle is a way to remember how V = IR rearranges to find any quantity when the other two are known: V = IR, I = V/R for current, and R = V/I for resistance.
Current (I) is the rate of flow of electrical charge through a conductor, measured in amperes (A). In a series circuit the current is the same at all points; it does not get used up as it flows around the circuit.
Resistance (R) is the opposition to the flow of current in a circuit component, measured in ohms (Ω). For the same potential difference, a higher resistance gives a lower current, because V = IR.
Current (I) is the rate of flow of electrical charge through a conductor, measured in amperes (A). Potential difference (V) is the energy transferred per unit charge between two points, measured in volts. Resistance (R) is the opposition to the flow of current, measured in ohms (Ω).
At constant temperature, resistance is directly proportional to wire length, so doubling the length doubles the resistance. Electrons have to travel further and collide with more ions in the metal lattice, so a longer wire has higher resistance and a lower current for the same voltage.
Current does not get used up as it flows around a circuit; this is a common misconception. In a series circuit the current is the same at all points, while the potential difference is shared across the components.
A longer wire has more resistance because electrons have to travel further and collide with more ions in the metal lattice, giving more opportunities for energy to be transferred. At constant temperature, resistance is directly proportional to wire length.
A 12 V battery connected to a 4 Ω resistor gives a current of 3 A. Current is found by rearranging V = IR to I = V/R, so I = 12 V ÷ 4 Ω = 3 A, and the unit is amperes.
Resistance is found with R = V/I, potential difference ÷ current. A component with 6 V across it and 0.5 A flowing through it has a resistance of 6 ÷ 0.5 = 12 Ω.
Current halves if resistance doubles, while doubling the voltage doubles the current. Current depends on both voltage and resistance, and current and resistance are inversely proportional for a fixed potential difference.
Current is measured in amperes (A), potential difference in volts (V) and resistance in ohms (Ω). These three quantities are connected by Ohm's Law, V = IR.
Ohm's Law was discovered by Georg Ohm in 1827. It connects current, potential difference and resistance in the relationship V = IR, which is the most important relationship in electronics.
Long cables and extension leads add resistance, because resistance is directly proportional to wire length. More resistance means a lower current for the same voltage, which is why a phone charges slowly through a long cable.