Author: Radoje Jankovic.

The figure from Jankovic dokumentation.

The bulb rated voltage is 4,5 V and the current Ib = 0,3 A. The resistance of rheostat is 10 Ohms and the battery voltage is 4 V.

The bulb is connected in the circuit as shown left and in the pictorial view right.

The nominal resistance of bulb is:

Rb = Ur/Ib

The current passing through the bulb when the rheostat R is in position (1) is:

I1 = U/(Rb + R)

where: Rb – bulb resistance; R – rheostat resistance.

In the position (2) of rheostat the current through the bulb is:

I2 = U/Rt

In the position (3) of rheostat, the current through the bulb is highest:

I3 = U/Rb.

You try to check the calculated values.