Question

An ammeter can be converted into a voltmeter by connecting
A. a low resistance in series
B. a high resistance in series
C. a low resistance in parallel
D. a high resistance in parallel

Answer 1

Hint: A voltmeter is a device connected in parallel to a component across which the potential difference must be found. An ammeter is a device attached in series in the circuit to measure the amount of current flowing through it. Both the devices must be designed such that they disturb the circuit as least as they can.

Complete answer:
We know that ammeters are used in series in a circuit and voltmeters in parallel to a circuit. In order for them to have negligible effect on other components and interfere with the experiment, the resistance in ammeter must be very small so that there is no potential difference across it. And for voltmeter, the resistance must be very high so that no current flows through it.
Now we are given an ammeter, which as we know is supposed to have very low resistance and have to convert it into a voltmeter. For this we will need to increase the resistance of the ammeter, this can be done by adding a very large resistance in series with the ammeter. And the complete system of resistance and ammeter will act a voltmeter.

Hence, the correct option is B, i.e. a high resistance in series.

Note:
An ammeter can detect a high range of currents and can be used here to detect and measure very high voltages due to the range of current it can measure. Although it is not advised to use them at such high voltages due to the danger of heavy heating of wires and resistance, which can destroy lab equipment.