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4.1 ELECTRICITY

P41 004.m

In the circuit shown, the ammeter measures the current drawn from the battery and the voltmeter measures the terminal battery voltage.

When the switch is closed, an additional resistance R₂ is added in parallel to the resistance R₁. How will the ammeter and voltameter readings change the when the switched is closed if (a) the internal resistance of the battery is zero and (b) the internal resistance is not zero?

View solution below only after you have completed the answering the question.

Solution

R_INT = 0

When the switch is closed, the two resistance both have the same terminal battery voltage across them. The voltmeter reading will not change. A current will now flow through both resistors, so more current is drawn from the battery. The ammeter reading will increase.

R_INT > 0

A current will now flow through both resistors, so more current is drawn from the battery. The ammeter reading will increase. But, there is a current through the internal resistance of the battery and consequently, a voltage drop across it. So, the terminal battery voltage must decrease. Therefore, the voltmeter reading will decrease.