Voltage
The electromotive force from a power source that pushes electrons through a circuit, often described as electric pressure. Measured in volts (V)
Current
The flow of electric charge through a circuit, caused by the movement of electrically charged particles, such as electrons. Measured in amperes (A)
Resistance
The opposition to the flow of electrons in an electrical circuit. It can be calculated using Ohm’s Law, which relates resistance (R), voltage (V), and current (I): R=V/I. Measured in ohms (Ω)
Power
Power is the rate at which energy is transferred or work is done.
Electrical Calculations
- Designers must understand the relationships between voltage, current, resistance, and power in order to specify components and troubleshoot circuits.
- The key equations come from Ohm’s Law and Power Law.
Key Equations
| Equation | Meaning | Units |
|---|---|---|
| $V = I × R$ | Voltage = Current × Resistance | V (volts), A (amps), Ω (ohms) |
| $P = V × I$ | Power = Voltage × Current | W (watts), V (volts), A (amps) |
Rearranging Formulas
To find any variable, rearrange the formula:
- $I = \frac{V}{R}$ → Current = Voltage ÷ Resistance
- $R = \frac{V}{I}$ → Resistance = Voltage ÷ Current
- $V = \frac{P}{I}$ → Voltage = Power ÷ Current
- $I = \frac{P}{V}$ → Current = Power ÷ Voltage
A resistor in a circuit has a resistance of 10 Ω, and a current of 2 A flows through it. What is the voltage across the resistor and the power used?
Solution
$$V = I × R = 2 \text{ A} × 10 \ \Omega = 20 \text{ V}$$
$$P = V × I = 20 \text{ V} × 2 \text{ A} = 40 \text{ W}$$
Real-World Examples
- Smartphones: Engineers calculate power consumption to optimise battery life and prevent overheating.
- Electric Vehicles: Understanding voltage, current, and resistance is crucial for designing efficient charging systems and motors.
- Renewable Energy: Solar panels and wind turbines rely on these calculations to convert energy efficiently.
- Calculate the current in a circuit with a voltage of 12 V and a resistance of 4 Ω.
- Determine the power consumed by a device with a current of 3 A and a voltage of 5 V.
