4.4- emf and internal resistance

Electromotive force

The amount of chemical energy converted to electrical energy per columb of charge when charge passes through a power supply

What is emf measured in

Volts

Symbol for emf

ε

Where does emf come from

Battery or power supply

What is emf equal to

Pd but when no current is flowing

How can emf be measured

By Connecting a high resistance voltmeter around the terminals of the cell in an open circuit

Internal resistance

Resistance that all power supplies have between their terminals

What does internal resistance cause over time

Loss of voltage or energy loss in a power supply

What happens if their is no internal resistance

Pd = emf

What happens if a cell has internal resistance

The terminal pd is always lower than the emf

How are lost volts represented

Lower case v- v

Lost volts

Voltage lost in the cell due to internal resistance

Lost volts formula

v= emf- terminal pd

EMF equation

Potential difference

Energy transferred per unit charge flowing from one point to another

EMF equation

Equation that links work done pd and charge

W=VQ

What do these 2 equations show?

1V= 1JC^-1

Equation that links work done elementary charge and pd

Electron volt

Unit of energy equal to the work done by an electron accelerated through a pd of 1V

Speed of an electron equation

Converting between joules and electron volts