Question

What will be the reading of a d.c. ammeter in a.c. circuit where the current flowing is 4A.

Answer 1

Hint: The device used to measure the direct current is called d.c. ammeter. When a resistor is placed in parallel with the Permanent Magnet Moving Coil galvanometer, the arrangement so formed is called the d.c. ammeter. And the instrument, which is used to measure the Alternating Current which flows through the branch of an electric circuit is called AC ammeter.

Complete answer:
The d.c. ammeter is a device which is used to measure the average value of the direct current which has a fixed or positive magnitude. And in the a.c. circuits the current is oscillating in nature so the average value will be always zero. Also, the d.c. current has frequency zero. So, for any magnitude of the current flowing in the a.c. circuit there will always be $0$ reading in the d.c. ammeter.
The average value will always come out to be zero for a full cycle in the a.c. circuit that is why d.c. ammeter is limited to the d.c. current. The a.c. the ammeter measures the R.M.S value in the circuit so, it won’t give any result in zero for either the d.c. current or the a.c. current. The R.M.S value does not mean the average value in a.c. circuit, it means root means square value.

Note:
Whenever we measure the d.c. Currently we need to use the d.c. ammeter and while measuring the a.c current always use the a.c. ammeter. The difference is that d.c. ammeter measures the average value of current in the circuit while a.c. ammeter measures the R.M.S. value of the current in the circuit.