Potential Dividers
Electrical Circuits - OCR A-Level Physics
Key Definition
potential divider
A circuit with two (or more) resistors in series that splits the source p.d. into smaller, usable output voltages.
A circuit with two (or more) resistors in series that splits the source p.d. into smaller, usable output voltages.
$$V_{out} = \frac{R_2}{R_1 + R_2} \times V_{in}$$
- A potential dividerA circuit that uses two or more resistors in series to produce a fraction of the source voltageThe energyThe capacity to do work. Measured in joules (J). transferred per unit chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). between two points. Measured in volts (V). Informal term for potential difference. across one of the resistors. provides an output p.d. less than the supply p.d..
- The ratio of p.d.s equals the ratio of resistances.
- Output is taken across one of the resistors.
- Any component connected in parallel with R_2 shares the same p.d. as R_2.
$$\frac{V_1}{V_{\text{out}}} = \frac{R_1}{R_2}$$
$$V_{\text{out}} = \frac{R_2}{R_1 + R_2} \times V_{\text{in}}$$
Potential dividerA circuit that uses two or more resistors in series to produce a fraction of the source voltageThe energyThe capacity to do work. Measured in joules (J). transferred per unit chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). between two points. Measured in volts (V). Informal term for potential difference. across one of the resistors. circuit with V_out taken across R_2
V_in across series pair R_1 and R_2. V_out is the p.d. across R_2 only.
Common Mistake
MEDIUM
Wrong: Using R_1 in the numerator when finding V_out across R_2.
Right: V_out across R_2 uses R_2 on top: $V_{\text{out}} = (R_{2} / (R_{1} + R_{2})) * V_{\text{in}}. The output resistor goes$ in the numerator.
Right: V_out across R_2 uses R_2 on top: $V_{\text{out}} = (R_{2} / (R_{1} + R_{2})) * V_{\text{in}}. The output resistor goes$ in the numerator.
Examiner Tips and Tricks
- The potential dividerA circuit that uses two or more resistors in series to produce a fraction of the source voltageThe energyThe capacity to do work. Measured in joules (J). transferred per unit chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). between two points. Measured in volts (V). Informal term for potential difference. across one of the resistors. equation only works when no currentThe rate of flow of charge. Measured in amperes (A). is drawn from the output.
- If a load is connected across R_2, the effective resistanceThe opposition to currentThe rate of flow of charge. Measured in amperes (A). flow. The ratio of potential difference to currentThe rate of flow of charge. Measured in amperes (A).. Measured in ohms (Ω). changes and you must recalculate.