Circuits (P1) Flashcards
Charge
Charge (Q)- a property of matter, can be positive or negative. Measured in Coulombs
Comes from the wires
Current
Current (I)- the rate of flow of charge- one Coulomb in one second is one Ampere (amp) (A)
Flows from positive to negative terminal
Potential difference
Potential difference (V)- the change in electrical potential energy between two points. Potential difference causes charge to move and current to flow. Measured in volts (V)
Resistance
Resistance (R)- a property of wires and components which makes it more difficult for charge to flow through. Measured in Ohms
How to connect an ammeter and a voltmeter
To connect an ammeter remove a piece and put the clips either side of where it was, to connect a voltmeter, put it either side of an existing piece
Series circuit rules
Current is the same everywhere
Total potential difference is shared between the components in proportion to the resistance
Resistance is the sum of each resistors resistance
Parallel circuit rules
Potential difference is the same in each path as the power supply
Current splits between the paths in proportion to the resistance
Resistance is lower than that of the lowest resistance
How and why are voltmeters and ammeters placed
Voltmeter in parallel as it measures p.d. throughout the circuit
Ammeter in series as it measures the current throughout the circuit
Equations
PIVIR
EVQIT
Power = current2 x resistance
A level potential difference calculation
V = W/Q
Kirchhoff’s first law
The sum of the currents going into the junction = the sum of the currents going out
Current is conserved
Current the same everywhere in series
Split between the branches in parallel
Kirchhoff’s second law
For any closed loop in a circuit, the sum of the potential differences across the components equals the potential difference of the power supply
Parallel each branch has the same p.d as power supply- split between components
Series p.d split between components
a level power equation.
P = V squared / R
