IGCSE 0625 · ELECTRICITY & MAGNETISM · 4.2

Electrical quantities

Charge, current, voltage and resistance, and electrical power and energy including the kilowatt-hour. It builds on energy from Topic 1 and leads into circuits and electrical safety.

TOPIC 4.2: ELECTRICAL QUANTITIES CAMBRIDGE IGCSE PHYSICS 0625 · PATHWAYS TheLucidSTEM · thelucidstem.com BUILDS ON 1.7 Energy LEADS TO 4.3 Circuits 4.4 Safety ELECTRICAL QUANTITIES 1 · CHARGE There are two kinds of charge: positive and negative. Like charges repel; unlike charges attract. Rubbing transfers electrons: one object becomes negative, the other positive. Conductors let charge flow; insulators do not. + − field lines run from + to − (Extended) 2 · CURRENT Current is the rate of flow of electric charge. Measured in amperes (A) with an ammeter placed in series. Direct current (d.c.) flows one way; alternating current (a.c.) keeps reversing. I = Q / t charge ÷ time (Extended) A ammeter (in series) a.c. d.c. 3 · VOLTAGE & RESISTANCE Potential difference is the energy given to or taken from each unit of charge. Measured in volts (V) with a voltmeter in parallel. Resistance opposes the current, in ohms (Ω). R = V / I I V resistor I V filament lamp I V diode These I–V graphs are an Extended idea. 4 · POWER & ENERGY Electrical power is the energy transferred each second. P = I V E = I V t Energy is often metered in kilowatt-hours (kWh): 1 kWh is a 1 kW device running for 1 hour. cost = number of kWh × price per kWh A 2 kW heater for 3 h uses 2 × 3 = 6 kWh. At a price of 0.20 per kWh, that is 1.20.
TOPIC 4.2: ELECTRICAL QUANTITIES CAMBRIDGE IGCSE PHYSICS 0625 · PATHWAYS TheLucidSTEM · thelucidstem.com BUILDS ON 1.7 Energy LEADS TO 4.3 Circuits 4.4 Safety ELECTRICAL QUANTITIES 1 · CHARGE There are two kinds of charge: positive and negative. Like charges repel; unlike charges attract. Rubbing transfers electrons: one object becomes negative, the other positive. Conductors let charge flow; insulators do not. + − field lines run from + to − (Extended) 2 · CURRENT Current is the rate of flow of electric charge. Measured in amperes (A) with an ammeter placed in series. Direct current (d.c.) flows one way; alternating current (a.c.) keeps reversing. I = Q / t charge ÷ time (Extended) A ammeter (in series) a.c. d.c. 3 · VOLTAGE & RESISTANCE Potential difference is the energy given to or taken from each unit of charge. Measured in volts (V) with a voltmeter in parallel. Resistance opposes the current, in ohms (Ω). R = V / I I V resistor I V filament lamp I V diode These I–V graphs are an Extended idea. 4 · POWER & ENERGY Electrical power is the energy transferred each second. P = I V E = I V t Energy is often metered in kilowatt-hours (kWh): 1 kWh is a 1 kW device running for 1 hour. cost = number of kWh × price per kWh A 2 kW heater for 3 h uses 2 × 3 = 6 kWh. At a price of 0.20 per kWh, that is 1.20.
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