# Physics

Chapter 5

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## 5.1-Circuit Rules

CURRENT RULES

At any junction in a circuit, the total current leaving the junction is equal to the total current entering the junction.

The current entering a component is the same as the current leaving component.

The current passing through two or more components in series is the same through each component.

POTENTIAL DIFFERENCE RULES

For two or more components in series, the total pd across all the components is equal to the sum of the potental difference across each component.

The pd across components in parallel is the same.

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Risistors in Series

R =R + R + R ....R

Resistance in Parallel

1/R =1/R +1/R +1/R....

The total current through the combination I =I +I =V/R +V/R

Resistance Heating

The heating of any component in an electrical current is due to the restance of the component because of repeated collisions of charge carriers with positive ions.

There is a net transfer of from charge carriers to positve ions. After a charge carrier loses kinetic energy in such a collision, the force due to the pd across the material aacelerates it until it collides with another positive ions.

the rate of heat transfer= I R

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## 5.3- Emf and Internal Resistance

INTERNAL RESISTANCEresistance inside a source of electrical energy; the loss of pd per unit current in the source when current passes through it.

ELECTOMOTIVE FORCE (emf )-the amount of electrical energy per unit charge produced inside a source of electrical energy.

FORMULA

THE PD ACROSS THE TERMINALS-is the elctrical energy per unit chargedelivered by the the source when it is in a circuit.

EMF=TERMINAL PD + 'LOST' PD

POWER

Power supplied by the cell, I =I R +I r

maximum power is delivered to the load when the load resistance is equal to the internal resistance of the source.

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## 5.3

Measuring of Internal Resistance.

The terminal pd decreases as the current increases. This is because the 'lost' pd increases as the current increases.

THE TERMINAL PD IS EQUAL TO THE CELL EMF AT ZERO CURRENT. This is because the lost pd is zero at zero current.

V= -Ir

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