# Proper voltage

Discussion in 'Homework Help' started by sidheshenator, Aug 23, 2009.

1. ### sidheshenator Thread Starter New Member

Aug 23, 2009
2
0
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.

Apr 5, 2008
18,339
3,514
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

3. ### mik3 Senior Member

Feb 4, 2008
4,846
69
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

4. ### sidheshenator Thread Starter New Member

Aug 23, 2009
2
0
thank you folks!!!!!!