Question

In this set of exercises (in the pre-lab AND lab), we will test/make the following assumptions: A flow exists in a complete circuit from one terminal of the battery, through the rest of the circuit, back to the other terminal of the battery, through the battery and back around i. the circuit. We will call this flow electric current For identical bulbs, bulb brightness can be used as an indicator of the amount of current through that bulb: the brighter the bulb, the greater the current. We will also see that, for identical bulbs, bulb brightness can be used as an indicator for potential drop across that bulb: the brighter the bulb, the greater the potential difference. ii. iii. Think of the DC power supply as a battery that is the agent that "pushes" or "drives" the current through the circuit. We can obtain a measure of the strength of the power supply (battery) by using an instrument called a voltmeter. When the terminals of a voltmeter (usually marked positive and negative) are connected to the corresponding terminals of a battery, the display indicates the strength of the power supply (battery), that is, the ability of the power supply (battery) to drive current through a circuit. The number obtained from this measurement is expressed in volts (V) and is commonly referred to as the voltage or potential difference of the power supply (battery), or more precisely, as "the potential difference across the power supply (battery)." Starting with these assumptions, we will develop a model that we can use to account for the behavior of simple circuits. The construction of a scientific model is a step-by-step process in which we specify only the minimum number of attributes necessary to account for the phenomena under consideration. 1. In order to measure voltages across circuit elements in a DC circuit, we say that we wire the voltmeter in parallel with the circuit element under test. In order+ to measure currents through circuit elements we say T that we wire the ammeter in series with the circuit element. Consider the circuit diagram at right. The voltmeter is in parallel with the light bulb (the circuit element) and the ammeter is in series with the light bulb. Suppose that you remove the voltmeter and replace it with either (i) a bare wire, (ii) another light bulb, or (iii) a broken wire as shown below. Ammeter Voltmeter Bare wire Broken ire Bulb (iii) If you wanted to keep the ammeter reading (essentially) the same as before, which would be the best choice? Explain.

Answer 1

The best choice would be replacing the voltmeter with a broken wire i.e the circuit (iii).

The battery can not push the flow when the wire is broken, it needs a closed path. The voltmeter across the bulb in the original circuit is measuring the potential difference across it. So there can't be an electric current in the voltmeter which is the same as broken wire. Thus the reading of the ammeter would be the same.