# How Many Amps flow through the lightbulb

1. Oct 31, 2009

### Mr530

http://img257.imageshack.us/img257/7161/physics.png [Broken]

I only have one more chance at this problem and I can't understand why it isn't 1. I assumed that power in = power out and power = current x voltage. If the voltage remains constant, wouldn't the current as well?

"In the circuit shown, how many volts are impressed across and how many amps flow through the lightbulb?"

(120V ac)--> 100 turns -->10 turns [1 A] --> 10 turns --> 100 turns --> lightbulb

Last edited by a moderator: May 4, 2017
2. Oct 31, 2009

### rl.bhat

Input power = [120V]*[I A]
Out put power = [..V]*[..A] ?

3. Nov 1, 2009

### Mr530

i'm still confused... are you saying 120v * 1 amp? Sorry, I am really bad at electricity, but dont the turns mean anything?

4. Nov 1, 2009

### rl.bhat

120v * 1 amp
It is not one, it is 'I'
In the first transformer, what is the out put power? From that find the input current.

5. Nov 1, 2009

### Mr530

so if I use V=IR how would I calculate I? I= V/R. but what do I plug in as the resistance? I am so bad at physics :(

6. Nov 1, 2009

### rl.bhat

From the tern ratio you can find the output voltage in the first transformer. The current is given. Find the output power. Equate it to input power and find the input current.

7. Nov 1, 2009

### Mr530

I am still confused. "The current is given?" maybe I am just fundamentally misinterpreting the diagram. Does it say "1A" or "IA." and either way, what does it mean?

8. Nov 1, 2009

### Mr530

I figured it out! Thank you so much!