Question

Alternating current cannot be measured by DC ammeter because:
A. AC cannot pass through the DC ammeter
B. The average value of current for the complete cycle is zero
C. AC is virtual
D. AC changes its direction

Answer 1

In the question, we need to establish a valid reason why an alternating current cannot be measured by DC ammeter. For this, we will use the properties of the alternating current and DC ammeter.

Complete step by step answer:

The current wave, which changes its direction as well as magnitude at regular intervals of time, is known as the Alternating Current, whereas the current wave, which does not change its direction during its transverse, is known as Direct Current.

Alternating Current is defined properly by three factors, i.e., frequency, phase angle, and absolute value, whereas for defining the direct current, we only need the absolute value.

An ammeter is an instrument that measures the flow of the current in a closed circuit (or path). It is always connected in series with the source so as to measure the total current flowing in the circuit.

DC ammeter always measures the average value of the wave passing through it.

The below figure is the pictorial description of alternating current and the direct current, respectively.

From the figures, we can see that the average value of the alternating current in a complete cycle is always zero as the positive trough and the negative crest will cancel each other and result in zero average currents.

Hence, the alternating current cannot be measured by DC ammeter because the average value of current for the complete cycle is zero.

Option B is correct.

Note: It is worth noting here that option D is also a correct statement that AC changes its direction, but it is not a suitable option with respect to the question so, students must be careful while selecting the options.