# DC Machines

## Homework Statement

A dc machine(6W, 120V,1500rpm) is separately excited and delivers rated current at rated terminal voltage.Field winding is connected to 120V supply. Rfw=100$$\Omega$$.
a) Determine the value of field current
b) Determine the value of Rfc required.

Vf= IfRf

## The Attempt at a Solution

In the question the value of Vf is given, while both If and Rf are variables. So I need another relation to find out both the values. Is there another relation that I'm missing?

## Answers and Replies

Unless I misunderstand the problem, you can get everything you need from the power equations P=IE and P=I^2*R.