# Homework question #1

Discussion in 'Homework Help' started by cgeorge5150, Oct 8, 2009.

1. ### cgeorge5150 Thread Starter New Member

Oct 8, 2009
9
0
A 500 Ohm resistive load, that is consuming 30W of power, is connected in series with a protection resistor across a 220V DC source. Determine the resistive value and teh power dissipated in the protection resistor.

2. ### hgmjr Retired Moderator

Jan 28, 2005
9,030
218
Have you taken a stab at solving the problem yourself? If so, go ahead and post your attempt and we can assist you with any problems you may be experiencing.

If you are stumped, then maybe you can describe what problems you are having setting up the problem.

Also, you need to differentiate your posts by using a different title for each. Posts with the same title make it difficult for members to find the one they are assisting you with.

hgmjr

3. ### cgeorge5150 Thread Starter New Member

Oct 8, 2009
9
0
I used I = sq root of (power/resistance) or sqr(30/500) = 250mA
R=220V/250mA = 880 Ohm.
P is 220V squared/880 = 55Watts

4. ### JoeJester AAC Fanatic!

Apr 26, 2005
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1,770
cgeorge,

Kirchoff's Voltage Law applies.

5. ### hobbyist AAC Fanatic!

Aug 10, 2008
885
87
First draw it up in schematic form

W = I^2 x R
W = E^2 / R
W = E x I

Then work with the equationS (plural) that has both variables in your schematic.

Then you should see clearly what the voltage should be across the unknown resistor.

6. ### mik3 Senior Member

Feb 4, 2008
4,846
69
Hints:

Calculate the voltage across the 500R resistor

The resistors are in series so they have the same current