Circuit Analysis and Electrical Measurements Understanding electrical circuits is a core topic in the OCR A Level Physics AS specification. This includes analyz...
Understanding electrical circuits is a core topic in the OCR A Level Physics AS specification. This includes analyzing series and parallel combinations of resistors, voltage dividers, potential dividers, internal resistance, electromotive force (EMF), terminal voltage, and using ammeters and voltmeters to take measurements.
When resistors are connected in series, the same current flows through each resistor. The total resistance is the sum of the individual resistor values. In contrast, parallel resistors have the same potential difference across them, and the total resistance is less than any individual resistor value.
Calculating the total resistance allows you to find the current flow and voltage drops across components using Ohm's law.
Find the total resistance of the following circuit:
Solution:
A potential divider consists of resistors in series with a voltage source, allowing different voltages to be 'tapped off' across the resistors. Voltmeters measure the potential difference across circuit components but must have high resistance to avoid loading effects.
In the following potential divider, calculate VX if VS = 9V, R1 = 3kΩ and R2 = 6kΩ.
Solution:
VX = (R2 / (R1 + R2)) × VS = (6 / (3 + 6)) × 9V = 6V
The current through a resistor can be measured using an ammeter connected in series. When connecting cells, their internal resistance causes the terminal voltage to be less than the EMF. Analyzing circuits with internal resistance is important for understanding practical applications.