The field coil of a DC generator has a resistance of 60 ohms.  The generator is supplied from a 240 Volt source.  What size resistor must be connected in series before the generator in order to maintain a maximum of 2 Amps in the coil? The field coil of a dc generator has a resistance of 60 ohms and is supplied from a 240 V source. If the current in the coil is to be limited to 2 A, calculate the resistance of the resistor that must be connected in series with the coil. What should the minimum rating of the resistor be?  

Expert Answers

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According to Ohm's Law, if the coil has 60 Ohms of resistance and can only support a 2 Amp load, the voltage must be decreased to

V = IR

V = 2A x 60 ohms = 120 Volts

Therefore, the series resistor must provide 120 Volts of drop from the 240 Volt source.  Again, using ohms law we can solve for the size of the resistor that will cause this to happen:

V(drop) = IR

R = V(drop)/I  =  120V / 2 amp = 60 ohms.

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