Note 8
EMF & Internal Resistance — AQA A-Level Physics
✓ ACCEPT
EMFElectromotive force. The energy transferred per unit charge by a source in driving charge around a complete circuit. Measured in volts (V). is the energyThe capacity to do work. Measured in joules (J). per unit chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). converted from chemical (or other forms) to electrical energyThe capacity to do work. Measured in joules (J). by the source. — Covers both marks: (1) energyThe capacity to do work. Measured in joules (J). per unit chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C)., (2) converted by the source.
✓ ACCEPT
The electrical energy transferred to each coulombThe SI unit of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. One coulomb is the charge transferred by a current of 1 A in 1 second. of charge by the powerThe rate of energy transfer. Measured in watts (W). supply. — 'Energy transferred to each coulombThe SI unit of charge. One coulomb is the charge transferred by a current of 1 A in 1 second.' = energy per unit charge. 'By the powerThe rate of energy transfer. Measured in watts (W). supply' = by the source.
✗ REJECT
EMFElectromotive force. The energy transferred per unit charge by a source in driving charge around a complete circuit. Measured in volts (V). is the voltageThe energy transferred per unit charge between two points. Measured in volts (V). Informal term for potential difference. of the battery. — Too vague. Does not state 'energy per unit charge' or mention the source. Zero marks.
✗ REJECT
EMFElectromotive force. The energy transferred per unit charge by a source in driving charge around a complete circuit. Measured in volts (V). is the force that pushes electrons around the circuit. — EMF is not a force. This is a fundamental misconception. Zero marks.
≈ CONDONE
EMF is the total p.d. across the cell when no currentThe rate of flow of charge. Measured in amperes (A). flows. — Operationally correct (V = epsilon when I = 0) but does not define what EMF IS. May get 1 mark for linking to measurement, but misses the 'energy per unit charge' mark.
✓ ACCEPT
EMF is the work doneEnergy transferred when a force moves an object. In electrical circuits, W = QV (charge times potential difference). per unit charge in driving charge around the complete circuit. — 'Work doneEnergy transferred when a force moves an object. In electrical circuits, W = QV (charge times potential difference). per unit charge' is equivalent to 'energy per unit charge'. 'Complete circuit' implies by the source. Full marks.