q6 calculate the value of the rheostat

Question

A 20ohm resistor is connected across a rheostat which is then connected in series with a heater element of 600W. What must the value of the rheostat be so that the heater draws 10A when the whole circuit is connected across a 100V supply.

Answer 1

Step 1:

A 20 resistor is connected across a rheostat.

Let R_h be the rheostat resistance.

A heater element is connected in series to it.

Power dissipated by heater element is 600 W.

Supply voltage is 100 V.

Current drawn by the heater element is 10 A.

Current in a series loop is same.

Current in the circuit is 10 A.

Draw a circuit with above specifications :

Step 2:

The power drawn by the heater element is given by .

Resistance of the heater element is 6 .

Resistor R₁ and Rheostat R_h are in parallel, then the parallel resistance is given as

Step 3:

Now apply Kirchoff's voltage law to the circuit.

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

Solution:

Resistance of the rheostat is set to 5 .