ELECTROMOTIVE FORCE. Consider the following diagram showing a circuit with an external resistance (R) internal resistance (r) and EMF ( ε ). When.

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Presentation transcript:

ELECTROMOTIVE FORCE

Consider the following diagram showing a circuit with an external resistance (R) internal resistance (r) and EMF ( ε ). When a battery goes dead it is because the internal voltage drop matches the EMF.

Example: If a 12.0 V battery has an internal resistance of ohms, what is the terminal voltage of the battery when a current of 3.00 A flows through the battery?

When a rechargeable battery is being charged an external voltage is applied to the battery. In order to force electrons backwards into the battery the external voltage must be greater than the EMF of the cell. In fact the external voltage must be:

Example: A 12.0 V car battery is being charged by an alternator that can supply 15 V. If the internal resistance of the battery is 1.3 ohms, what is the current through the battery?