# D.C Circuits

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• Created by: Murray_R
• Created on: 15-12-13 18:18

## Circuit rules

• At any junction the total currnet leaving the junction has to be equal to the current entering the junction
• In seris the current entering the component in the same as the current leaving the component (current is not used up)
•  in seris the current passing thought two or mor coponents in seris is the same throught each component(the current splits equally)
• for two or more components in seris , the total pd across all the components is equal to the sum of the potential differences across each component (V =V +V =V)
• the pd across components in parrallel is the samr
• for any complete loop of a crcuit, the sum of the emf round the loop is equal to the sum of the pd round the loop.
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## More Resistance

• in seris R=R +R +R ....
in paralel 1/R=1/R +1/R ...
• Resistance Heating=rate of heat transfer=I R
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## EMF & Internal Resistance

• EMF=eletromotive fource is the electrical energy per unit charge produced by the battery
• the internal resistance of a source is the loss of p.d per unit current in the source when current passes throught the source]

=IR+Ir
power supplied by the cell=I  =I R+I r

• Maximum power is delivered to the load when the load resistor is equal to the internal resistance of the source
• when a graph of voltage (Y) is plotted against current (X) the y intercept= the EMF and the gradient is th einternal resistance
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## More Ciruit calculations

• always draw the circuit diagram

PD across each resistor=Currentxeach resistors resistance

• is a cell is connectedin seris in the same direction of the circuit the voltage is the two voltages added to gether
• if the cells are connected in opposites then the EMF is the difference between the two values

cells in parrallel
V=   -I/R

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## The Potential Divider

• this is two or mor resistors in seris with a source of fixed petential difference it can be used to supply a pd of a fixed value between 0 and the source pd, to supply a varied PD and to deliver a pd that varies with temperature conditions
• the ratio of the pds across each resistor is equal to th eresistance ratio of the two resistors
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