P4 Electric Circuits - AQA Trilogy Physics

Circuit Symbols

Current

• electrons passing through a circuit

• charge flow (C) = current (A) x time (s)

• Q = I x t

Potential Difference / Voltage

• potential difference (V) = energy transferred (J) / charge (C)

• V = E / Q

Resistance

• resistance (Ω) = potential difference (V) / current (A)

• R = V / I

Ohm’s Law

• the current through a resistor at a constant temperature is directly proportional to the potential difference across the resistor

Filament Lamp

• the resistance increases if the temperature increases

Diode

Thermistor

• resistance decreases if the temperature increases

Light-Dependant Resistor (LDR)

• resistance decreases as the light intensity increases

Series Circuit

• the current in each component is the same

• the total potential difference is shared between components

• adding components resistances gives the total resistance

• adding more resistors increases the total resistance - the current through the resistors is reduced and the total pd across them is unchanged

Parallel Circuit

• the total current is the sum of the currents through the separate components

• the pd across each component is the same

• the bigger the resistance of a component, the smaller the current that will pass through

• adding more resistors decreases the total resistance - the total current through the resistors is increases and the total pd is unchanged