A-Level Physics · Topic 5
Electricity and circuits: every key term you need (+ practice quiz)
16 flashcard terms for A-Level Physics Topic 5, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 8-question quiz — free, no account needed.
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Electric current Rate of flow of charge, measured in amperes. One ampere is one coulomb per second.
Potential difference Energy transferred per unit charge between two points, measured in volts. One volt is one joule per coulomb.
Electromotive force Energy supplied per unit charge by a source. Unlike potential difference, it refers to energy delivered to the circuit, not taken from it.
Resistance Potential difference divided by current. A component is ohmic only if this stays constant as current changes.
Ohm's law Current is proportional to potential difference, provided temperature and other physical conditions stay constant.
Resistivity A property of the material, equal to resistance times cross-sectional area divided by length. Measured in ohm metres.
Filament lamp characteristic A curve, not a straight line: rising temperature increases lattice vibrations, so resistance grows with current.
Thermistor A negative temperature coefficient thermistor's resistance falls sharply as it warms, because more charge carriers are released.
Light dependent resistor Resistance falls as light intensity rises, since more charge carriers are freed. Used in light-sensing potential divider circuits.
Kirchhoff's first law Total current into a junction equals total current out — a statement of conservation of charge.
Kirchhoff's second law Around any closed loop, the sum of electromotive forces equals the sum of potential drops — conservation of energy.
Internal resistance Resistance within the source itself. It causes lost volts, so terminal potential difference falls as current rises.
Potential divider Two resistors in series split the supply voltage in proportion to their resistances, giving a controllable output.
Superconductivity Below a critical temperature, resistivity drops abruptly to zero. Allows currents to persist with no power dissipation.
Power in a circuit Current times potential difference, which can also be written as current squared times resistance.
Root mean square value The steady direct value delivering the same mean power as an alternating supply. Equal to the peak value divided by the square root of two.
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