Unfortunate book

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A circuit must contain a source of potential difference, and a path for the flow of charge. It will probably also contain a load or resistance (a user of energy).

Charges moving through a cell experience a voltage rise equal to the potential difference between the terminals. As the charge moves through the external circuit it experiences a voltage drop equal in magnitude to the initial voltage rise.

In any circuit, the total of all voltage rises is equal to the total of all voltage drops. This is one of Kirchoff’s laws for electric circuits.

The emf of the circuit is the drop in potential across the total circuit, but Ohm’s law (V = IR) applies equally well to any part of circuit that does not include a source of emf.

If a circuit contains a load with a resistance R, and a source with an emf , the current in the entire circuit is I = /R.

A battery has an emf of 12.0 volts . The load has a resistance of 6 ohms. What are the total resistance and current of the circuit?

For a part of the circuit Ohm’s law is: V = IR.

What is the drop in potential across the external circuit in the previous example?

Notice that the drop in potential adds up to the total emf of the battery.

A good voltmeter has a high resistance. If it is connected across the terminals of a source of emf, negligible current is drawn from the source and the voltmeter registers the emf of the source.

A dry cell gives an open-circuit voltmeter reading of 1.5 V. The voltmeter is then removed from the circuit and a load of 3 Ω is added. What will an ammeter in the external circuit read?