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Module 4 - Chapter 10 - Electrical circuits I - Coggle Diagram
Module 4 - Chapter 10 - Electrical circuits I
Laws
1st law - sum currents in a point = sum of currents out of a point
2nd law - In any circuit, the sum of electromotive forces is equal to the sum of the pds around a closed loop
Closed loop - single possible path for the current
2nd law rephrased - total energy transferred to the charges in a circuit equal the total energy transferred from the charges
series circuit
Charge
Current is the same at all positions
Charge isn't used up, just flows around the circuit
One path for the current, single loop from one terminal to the other
EMF
One source
If components with different resistances, component with the higher resistances takes a greater proportion of the EMF
If the circuit has two components of the same resistance, the emf is shared equally between them
More than one source
If emf sources are connected with opposing polarities, sum of emfs is the difference between the sources
If the circuit has more than one source of emf, the emf from each source must be added before sharing between components
EMF is shared between components and sum of pd across components equals the emf
Adding components in series reduces the emf that is shared between original components
Parallel circuits
Charge
More than one possible path for charges
Greater the resistances of the branch, the lower the current that passes through it
If one branch has half the resistance of another, twice the current will flow through it
Each branch can be thought of as a seperate circuit, changed to one brance doesn't affect other brances
EMF
Total pd across each branch equals the emf from the power supply
Several different loops, each branch forms a loop
If a branch has many components, the sum of pds across these components equals the emf
Combining resistors
Series
Each additional resistor effectively increases the length of the path taken by the charges, so increases the resistance
Total resistances of resistors in series equals the sum of the individual resistors
Parallel
Addition resistors provides another path for the current, which increases the cross sectional area and lowers the resistance
Total resistance is always lower than the resistance of any resistor in combination
Potential divider circuits
Potential dividers
Vary the pd across an output when connected to a fixed input
A circuit can be connected across one of the resistors in parallel
Pd supplied to the circuit can be varied to any value from zero to the EMF supplied from the power source depending on the resistance of the resistors
Pd across each resistor must always add up to the pd from the power source
Ratio of resistances
Pd across each resistor in a potential divider depends on their resistances
If the resistors have the same resistance, pd is shared equally
If one has twice the resistance, it will receive two thirs of the pd
Equation
Loading a potential divider
Connecting a component or circuit to V out
Placing a component in parallel with R2
Lowers the resistance of this part of the potential divider circuit, which lowers the fraction of the total pd across this part of the circuit, so lowers V out
Adding a large load (high resistance) to the circuit has little effect on V out
Adding a small resistance reduces V out significantly
