A student has begun building a multimeter in the lab and then leaves for lunch.
ID: 306379 • Letter: A
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
If the multimeter is on very low resistance setting then there must be an external high resistance connected with the multimeter in parallel i.e the multimeter will act like an ammeter and can measure current in the circuit.
If the multimeter is on very high resistance setting then there must be an external high resistance connected with the multimeter in series i.e the multimeter will act like a voltmeter and can measure voltage in the circuit.
Thus, the high resistance setting of the multimeter will be for voltage and the low resistance setting will be for measuring the current.
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