Worked Example: EMF & Internal Resistance
Electrical Circuits - OCR A-Level Physics
Worked Example
A solar cell has an open circuit 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. of 8.2 V. At its typical operating point, the currentThe rate of flow of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. Measured in amperes (A). is 100 mA and the terminal p.d. is 5.5 V. Determine the internal resistanceThe opposition to currentThe rate of flow of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. 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).The resistanceThe opposition to current flow. The ratio of potential difference to current. Measured in ohms (Ω). within the source of EMFElectromotive force. The energy transferred per unit charge by a source in driving charge around a complete circuit. Measured in volts (V). itself, which causes energyThe capacity to do work. Measured in joules (J). to be dissipated inside the source. of the cell.
Show Solution
1
Identify known values
2
Write the EMFElectromotive force. The energy transferred per unit charge by a source in driving charge around a complete circuit. Measured in volts (V). equation
3
Rearrange for r
4
Substitute and calculate
Answer
The internal resistanceThe opposition to current flow. The ratio of potential difference to current. Measured in ohms (Ω).The resistance within the source of EMFElectromotive force. The energy transferred per unit charge by a source in driving charge around a complete circuit. Measured in volts (V). itself, which causes energyThe capacity to do work. Measured in joules (J). to be dissipated inside the source. of the solar cell is 27 ohms.