Circuits, Current, Voltage & Resistance
Electric circuits transfer energy via the flow of charge (current) driven by a potential difference (voltage) and opposed by resistance. Applying Ohm's Law (V = IR), series and parallel circuit rules, I-V characteristics of components, and electrical power equations (P = VI and P = I²R) underpins GCSE Physics Paper 1.
- Current
- The rate of flow of electric charge, measured in Amperes (A).
- Voltage (Potential Difference)
- The energy transferred per unit charge passed, measured in Volts (V).
- Resistance
- The opposition to current flow in an electrical circuit, measured in Ohms (Ω).
Electric Field Simulator & Interactive NPN Transistor Builder
Adjust charges and distances to visualize Coulomb’s Law field lines, or switch to the Transistor Lab to wire and test an NPN circuit.
1. Coulomb’s Law Point-Charge Calculation
Formula: F = k · |Q₁ · Q₂| / r² where k = 1/(4πε₀) = 8.99 × 10⁹ N·m²·C⁻²
3.60 N
Attractive (towards each other)7.19e+6 N/C
At r/2 = 0.10 m2. Uniform Parallel-Plate Field Calculator
Formula: E = V / d (units: V m⁻¹ or N C⁻¹)
Key Concepts & Exam Definitions (6)
- Current
- The rate of flow of electric charge, measured in Amperes (A).
- Voltage (Potential Difference)
- The energy transferred per unit charge passed, measured in Volts (V).
- Resistance
- The opposition to current flow in an electrical circuit, measured in Ohms (Ω).
- Charge
- A fundamental property of matter that experiences a force in an electromagnetic field, measured in Coulombs (C).
- Diode
- A component that allows current to flow in only one direction.
- Thermistor
- A resistor whose resistance changes with temperature; as temperature increases, resistance decreases.
Quick-Fire Flashcards (6)
Click any card to check the answer, then mark it as Known to track your progress.
What is the unit of electrical current?
What is the formula linking voltage, current, and resistance?
How does resistance add up in a series circuit?
What happens to the current in a parallel circuit?
What is the purpose of a fuse in a plug?
What color is the Earth wire in a standard UK plug?
Exam-Style Questions & Mark Schemes (4)
Write or think through your answer first, then click Check Mark Scheme to see the exact points examiners award marks for.
- Q1
A circuit has a 12V battery and a resistor of 4Ω. Calculate the current flowing through the circuit.
Click “Check Mark Scheme” to compare your answer, Current (I) = V / R = 12 / 4 = 3 Amps.
- Q2
Explain how the resistance of an LDR changes as light intensity increases.
Click “Check Mark Scheme” to compare your answer, As light intensity increases, the resistance of an LDR decreases.
- Q3
Calculate the energy transferred when a charge of 5 C passes through a potential difference of 10 V.
Click “Check Mark Scheme” to compare your answer, Energy = Charge × Voltage (E = Q × V). Energy = 5 × 10 = 50 Joules.
- Q4
If two 5Ω resistors are connected in series, what is the total resistance?
Click “Check Mark Scheme” to compare your answer, Total resistance = 5Ω + 5Ω = 10Ω.
Common Exam Questions (3)
What is Ohm's Law?
Ohm's Law states that the current flowing through a metallic conductor is directly proportional to the potential difference across it (V = IR), provided the temperature remains constant.
What is the difference between series and parallel circuits?
In a series circuit, all components are connected in a single loop, so the current is the same everywhere and the supply potential difference is shared between components. In a parallel circuit, components are connected on separate branches, so the potential difference across each branch equals the supply voltage and the total current splits between the branches.
How do you calculate electrical power?
Electrical power is calculated using Power = Potential Difference × Current (P = VI) or P = I²R, where power is measured in watts (W), potential difference in volts (V), and current in amperes (A).
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