Physics 4.3 (Electrical circuits) Flashcards
What is Kirchoff’s first law?
-The sum of the currents entering a junction is equal to the sum of the currents leaving the junction
What is Kirchhoff’s second law?
-The sum of the electromotive force is equal to the sum of the products of the current and the resistance in a closed loop
What are the rules for current, e.m.f and resistance in a series circuit?
-Current has the same value everywhere
-E.m.f of the cell is equal to the e.m.f across the components
-The total resistance is equal to the sum of the individual resistors
What is the rule for voltage and current in a parallel circuit?
-The total voltage is the same on each branch of the parallel circuit as the cell
-The total current of the cell splits up between the branches depending on their resistance, less current will flow where there is more resistance (V=IR)
Do Revision cards
What is a potential divider?
-A circuit that contains two resistors connected in series to split the voltage into a ratio so that a chosen voltage can be provided to a device/circuit.
How would you use a potential divider to use a thermistor and a LDR?
-Create a Circuit with a resistor and an LDR or thermistor and attach the circuit for a heater or light around the thermistor or LDR
-When the light or temperature is low the resistance is high so your circuit will get lots of P.D but as the light/temperature increases resistance goes down decreasing the p.d share and turning of the heater or street lamp
What is the terminal P.D?
-The p.d across the terminals of the cells
-The e.m.f minus the terminal p.d is equal to the lost volts/internal resistance
