Unit 2 - D.C Circuits Flashcards
Explain 3 things about series circuits
1) electricity has 1 path to flow through.
2) current stays the same throughout series circuit. This obeys the law of conservation of charge.
3) Sum of the potential difference (voltage) across all the components is equal to the potential difference (voltage) of the source (the battery), this obeys the law of conservation of energy.
Explain 3 things about parallel circuits
1) electricity has 2 or more paths to flow through before the paths combine together again.
2) the current in each branch add up to the current through the source (the battery). This obeys the law of conservation of charge.
3) The potential difference (Voltage) across each branch is equal. This obeys the law of conservation of energy.
Define electro motive force (emf)
energy converted from some other form (eg. Chemical) to electrical potential energy per coulomb of charge flowing through the source
Define potential difference (p.d)
the energy changed from electrical potential energy to another energy per charge passing between two points. (aka voltage)
How to calculate total resistance in series and parallel
Series = Rtotal = R1 + R2
Parallel = 1/Rtotal = 1/R1 + 1/R2
then you rearrange and flip1/Rtotal to Rtotal/1, calculate it and get the answer
(remembe this it wont be in exam)
What is the potential divider
Circuits with 2 resistors and an emf. Usually a fixed resistor and a variable resistor or thermistor or LDR. potential dividers are circuits which aim to deliberately divide the potential difference (voltage) from a sourfce to 2 or more components. P.D shared based on resistance. (more resistance more voltage, directly proportional)
What is potential divider used for
used when a certain output p.d is required.
what are Thermistors used for in a potential divider circuit?
Can be used to alter the output of the device.
EG. in a temperature sensing system,as temperature increases, the resistance of thermistor decreases, and p.d across the fixed resistor increases.
Temperature decrease = opposite
What is light dependant resistor (LDR) used for in potential divider circuit?
Can be used to alter the output of the device.
EG. in a light sensing system, as light intensity increases, resistance of LDR decreases, and so potential difference across it decreases.
Light decreasing = opposite
What is the equation to calculate EMF
V = E-Ir
V is pd across resistor R
E is EMF from cell
Ir is lost volts in cell due to internal resistance
What happens when more than 1 voltage source is used?
When the voltage sources are in series facing the same direction, their EMF adds up.
If the voltage sources are facing in opposite directions, their EMF subtracts.
What is kirchoff’s 1st law?
At a junction in a circuit, the sum of the currents entering the junction is equal to the sum of currents leaving the junction
What is kirchoff’s 2nd law?
In any closed loop, the sum of emf is equal to the sum of the pd’s around the loop
What is the principle of conservation of charge
Electric charge cannot be created or destroyed, (though positive and negative charges can neutralise each other) charge cannot pile up at a point in a circuit
What are kirchoff’s 1st and 2nd law a consequence of?
1st consequence of charge
2nd consequence of energy
