00:01
Hello, in the question we have given that, so we have to tell what happens to the speed of a separately excited dc motor if a resistor is placed in series with the field winding.
00:19
So now here let us see what it does.
00:24
So we are having this circuit.
00:31
So this is part a we are doing.
00:33
So here we have this motor and then we have a resistor and here we have the winding coils.
00:55
So here let us call this as variable resistance rf for instance.
01:03
So now see the current is flowing like this.
01:08
So this is the source voltage.
01:10
Now so what we do not have to solve this circuit as such.
01:14
So let us write one formula.
01:16
So we have n is directly proportional to v minus iara, it is iara plus r divided by this phi where this phi is the flux.
01:35
Now so if the flux decreases, so the speed will increase so and vice versa...