ANS: Electric current is the flow (movement) of electric charge. I = q/t Where I = current in amps (A) q = charge in Coulombs (C) t = time (s) Symbol : IUnits: Amperes (A) Current is measured with an ammeter placed in series in the circuit Conventional current is where electrons travel from +ve to – ve. Natural current is where it travels from a build up of –ve charge to an area deficient in –ve charge namely and area of +ve charge DO EXERCISES PAGE 156 RUTTER DO EXERCISES PAGE 156 RUTTER

ANS: Voltage (sometimes also called electric or electrical tension) is the difference of electric potential between two points of an electrical or electronic circuit, expressed in volts V = I/q Where V = voltage in volts (V) I = current in amps (A) q = charge in Coulombs (C) Symbol : VUnits: Volts (V) Often thought of as the change in energy as the charge moves between two points.

 E = Vq Thus: Where  E = change in energy (J) V = voltage in volts (V) q = charge in Coulombs (C) The voltage between two points, distance apart ‘d’, in an electric field ‘E’ V = Ed F = Eq Where E = electric field strength F = force on the charge (N) q = charge in Coulombs (C) DO EXERCISES PAGE RUTTER DO EXERCISES PAGE RUTTER

ANS: is defined as the rate at which electrical energy is transferred by an electric circuit. P = IV Where P = power in watts (W) I = current in amps (A) V = voltage in volts (V) Symbol : PUnits: Watts (W) DO EXERCISES PAGE RUTTER DO EXERCISES PAGE RUTTER

ANS: is defined as a measure of the degree to which an object opposes an electric current through it V = IR Where R = resistance in ohms (Ω) I = current in amps (A) V = voltage in volts (V) Symbol : RUnits: Ohms (Ω) Resistance occurs in all conductors. A good conductor has low resistance and vice versa. The current in a conductor depends on the resistance and the voltage applied across it, Ohm’s Law). Resistance often very large kΩ or MΩ

RESISTANCE IN SERIES & PARALLEL R1R1 R2R2 A V1V1 A2A2 V2V2 A V R2R2 R3R3 A3A3 A1A1 I1I1 I2I2 I3I3 V I I I SERIESPARALLEL The current, I, measured by each ammeter has the same value in each part of the circuit. The voltages across the series resistors add up to the supply voltage V s = V 1 + V 2. The equivalent resistance, R s, of the whole circuit is given by: R s = R 1 + R 2. The currents in the parallel components add up to the current from the supply, ie I 1 = I 2 + I 3. The voltage is the same across all branches in parallel The equivalent resistance, R s, of the whole circuit is given by: 1/R p = 1/R 2 + 1/R 3.

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