Physics circuits 21st March - 28th April 2017

• When 2 insulators are rubbed together electrons are transferred 
• Some will gain some will lose
• Happens on surface

Polythene rod > negative

Perpex rod > positive

• A battery = two or more cells
• Size of elctric current > the rate of flow of charge

Charge flow (C) = current, I (A) x time taken

Charge = energy per charge as it travels around a circuit

Potential difference, V = energy transferred / charge, Q (coulombs)

Resistance (ohms) = potential difference, V (volts) /

                                   current, I (amps)

Ohms law >  the current through a resistor at a constant temperature is directly proportional to the potential difference across a resistor

• A filaments lamp's resistane increases if th filament's temp increases
• A thermisistor's resistance decreases if the temp increases
• A LDR's resistance decreases if the light intensity increases

• The total current = sum of the currents through the seperate components
• the potential difference across each component is the same

Current, I (A) = potential difference (V) / component's resistance, R (ohms)

Adding more resistors in a parallel decreases the total resistance because the total current through the resistors is increased and the total potential difference across them is unchanged.