Question

In a DC generator, the induced emf in the armature coil is
A- DC
B- AC
C- Fluctuating DC
D- Both AC and DC

Answer 1

Hint: Have a good idea about the working of a dc generator and then about production and interconversion of current from one form to another. With that we are good to go.

Complete step by step answer:
When an electric generator is made to work, there will be a rectangular coil placed inside the generator which would be mounted by a magnetic field by the electromagnets which are placed around it. Then, the split ring commutator (which is used for the transfer of current into and out of the generator) passes the Ac current to the coil.
The split ring commutators are designed in a manner to transfer current (AC) in and out without being affected by the rotational motion of the generator. They pretty much look like a copper ring split in the middle.
As the current flows into the coil a torque is generated in the coil which makes the coil rotate within its axis continuously. To prevent the torque from reversing (reversing of torque would have a retarding action on the coil which I undesirable) the rectangularly shaped coil moves through the plane perpendicular to the magnetic field around it.
As, you have seen it is the split rings which reverses the current at the right point and thereby helping in maintaining the direction of the current, making it appear as if the generator itself was producing direct current. Whereas the induced emf in the armature is alternating due to its rotational nature.

So, the correct answer is “Option B”.

Note:
We might be tempted to believe that the emf is DC as it is a DC generator.
Also, the output voltage is a fluctuating DC, but that is not what’s been asked, which is why it’s important to read and understand questions properly.
The rectangularly shaped coil moves through the plane perpendicular to the magnetic field around it.