Question

A 4-range milliammeter having ranges of 0-10mA, 0-50 mA, 0-100 mA, 0-500 mA. It is used for measurement of current whose magnitude is not known. In order to prevent damage to the instrument, the selector switch of the ammeter should be first placed at

• A. 0-10 mA
• B. 0-50 mA range
• C. 0-100 mA range
• D. 0-500 mA range

Hint:

Using Multi-Range Meters. When measuring an unknown quantity (current or voltage), always start with the highest range setting to prevent instrument damage. Then reduce the range as necessary for an accurate reading.

Answer 1

The Correct Option is D

When measuring an unknown current (or voltage) with a multi-range instrument, it is crucial to avoid overloading and potentially damaging the instrument's sensitive movement
To ensure safety, one should always start the measurement by selecting the highest possible range
If the reading obtained on the highest range is very small or off-scale low, then progressively lower ranges can be selected until a suitable on-scale reading with good resolution is obtained
Starting on a low range with an unknown, potentially high current could cause the meter needle to deflect violently past full scale, damaging the movement
Therefore, the selector switch should first be placed at the highest range, which is 0-500 mA