Helpmyphysics

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The Wheatstone Bridge is used to find the value of an unknown resistor.

When there is no p.d. across the bridge the we say the Wheatstone Bridge is balanced.

If the value of resistance in the decade box is changed then it follows there is a direct proportional change in the current that will flow across the bridge.

Provided the resistance is not changed too much away from the balance point then it can be written

Further info about the Wheatstone Bridge
BBC Bitesize Higher Physics: Wheatstone Bridge.

In the simulation below it can be seen that when electric current is taken from an electric cell the potential difference between the terminals decreases.

When no current is taken the tpd is at its maximum. This is the EMF of the electric cell.

The EMF of an electric cell is the maximum energy given to each Coulomb of electric charge.

This lost energy per coulomb, usually called "lost volts" is lost in the internal resistance of the electric cell.

You can download a poster for your notebook below.

InternalResistance

Hi physics lovers. Check these two videos below on internal resistance.

How to calculate the internal resistance of a cell.

Investigating the internal resistance of a cell.

You can download the physics simulation from the here:

PhET Electrical Circuit Simulation