A 100V, 60 W bulb is connected in series with 100V, 100W bulb and the combination is connected across 200V mains. Find the value of resistance that should be connected across the first bulb, so that each bulb may prope current at proper voltage.

 

Hello,

Just take it apart:
How much current is flowing through the 100W bulb at 100 Volts?
How much current is flowing through the 60W bulb at 100 Volts?

The difference of these currents must flow through the resistor.
If you know the voltage and the current for the resistor, you can calculate it.

Now upto you.

Greetings,
Bertus

 

To have a voltage drop of 100V both bulbs should be of the same wattage. The first bulb is 60W, thus you need 40W more to equal 100W (the second bulb).

Thus the resistor needs to dissipate 40W

R=V^2/W=100^2/40=250 R

 

thank you folks!!!!!!