Step 1:

A 20 resistor is connected across a rheostat.

Let R_h be the rheostat resistance.

A heater is connected in series to it.

Power dissipated by heater is 600 W.

Supply voltage is 100 V.

Current in the circuit is 10 A.

Draw a circuit with above specifications :

The power across the heater is given by .

Current in a series loop is same.

Resistance provided by the heater is 6 .

Step 2:

Here R₁ and R_h are in parallel, then the equivalent resistance is given as

Now apply Kirchoff voltage law.

The value of the rheostat must be 5 so that heater draws 10 A of current.

Solution:

Resistance provided by rheostat is 5 .