Question

a coil develops heat of 800 cal/sec .when 20 volts is applied across its ends.what is the resistance of coil?

Answer 1

Power dissipated by a resistor coil =  P = I^2 * R = V^2 / R
     V = voltage across resistor,  I = current thru the resistor and  R = resistance
                 R = V^2 / P

             R = 20^2 / [ 800 cal /sec * 4.184 Joules/cal ]
               = 0.1195 ohms