# Difference in Potential

1. Five similar lamps are connected in series to a source providing a difference of potential of 550 V.
A) What is the difference of potential across each lamp?
B) If the current flowing in the circuit is 1.10 A, what is the resistance of each lamp?
C) What is the resistance of all five lamps?

2. R = V/I

A) To find the difference of potential across each lamp, I believe you would divide the source difference of potential by 5, giving you 110
B) To find the resistance, Ohm's Law can be re-arranged, giving you R = V/I. I believe dividing the SOURCE different of potential by the given current would give you (550v / 1.10 a) = 500 ohms

C) Last but not least, to find the total resistance, we would just multiply the resistance found in part B times 5 (for each lamp) giving us 2500 ohms

Have I made a mistake in my thought process? If someone could confirm my attempt, it would be appreciated.

looks good to me.

Ok, I'm only unsure for parts B and C, because I didn't know whether to use the difference of potential solved in part A for parts b and c.

nrqed
Homework Helper
Gold Member
Ok, I'm only unsure for parts B and C, because I didn't know whether to use the difference of potential solved in part A for parts b and c.

If you use the total potential difference, 550 V, the resistance you find is the total resistance of all the lamps, not the resistance of one lamp.

ranger
Gold Member
Part A is correct.

Part B gives the total resistance of the circuit.

Part C. Theres a mistake. If you know V for each bulb is 110V and the current through it is 1.10A. Therefore R = V/I = 110/1.10 = ?

EDIT: didnt mean to step on your toes nrqed.

er right. Blew that one on this end. assumed he used the V across the lamp to get R, not the total V.

Thanks so much for your help.. It seems I have one more queston..

If you know the resistance of two resistors (connected in series) as well as the current flowing through them, how do you find the difference of potential across each resistor?

ranger
Gold Member
Thanks so much for your help.. It seems I have one more queston..

If you know the resistance of two resistors (connected in series) as well as the current flowing through them, how do you find the difference of potential across each resistor?

V = IR

**********filling in space

D'oh.. I should have thought of that.

Would I use that formula for EACH resistor, or could I use it once using the Total resistance?

**EDIT**
Retract that, using the total resistance would give me the same result if I just added together the two differences of potential I'm solving for.

Last edited:
ranger
Gold Member
If you want to find the voltage across individual resistances then you use V = IR, where R is individual resistance. This can also be applied on a larger scale.