A student has begun building a multimeter in the lab and then leaves for lunch.

Question

A student has begun building a multimeter in the lab and then leaves for lunch. The multimeter has three settings, OFF, VOLTAGE, and CURRENT. Whether the multimeter functions as an ammeter or a voltmeter is determined by the internal resistance (high or low) of a particular setting. The first student forgot to label the settings before he left. The display gives a number without units. The components of the multimeter are not encased, and the user can see whether the internal resistance is high or low. A second student comes into the lab and uses the multimeter. He wishes to measure the current through a bulb and the voltage across a bulb when the bulb is connected to a battery. The only information he has about what setting the multimeter is on is from the resistors. Explain how he will determine which setting is for voltage and which is for current.

Explanation / Answer

We know while measuring the current the multimeter has to be used as ammeter in that
case the internal resisitance of multimeter should be low.
Hence when we have to use it as multimeter we kept the internal resistance low and bulb will be in series with the resistance.
Now if we have to use it as voltmeter than the internal resistance shouuld be high.
Hence when the internal resistance is kept high then we have to connect the bulb in parallel condition for meausrement of the voltage.

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