# Homework Help: Why don't all lights turn off when connected in parallel

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1. Jan 21, 2016

### prishila

1. The problem statement, all variables and given/known data
When the filament of a light is broken why do others continue to light?

2. Relevant equations
Parallel: U=U1=U2=U3
I=I1+I2+I3+...

3. The attempt at a solution
Is it because there are some nodes? How can you explain this simply?

2. Jan 21, 2016

### CWatters

So what happens (for example) to U2 and I2 if Bulb 1 or 3 fails?

3. Jan 21, 2016

### prishila

U2 doesn't change and I2 ... I don't know, it becomes greater?

4. Jan 21, 2016

### cnh1995

Consider three bulbs in parallel and U1=U2=U3. If bulb 1 fails, how will it affect U2 and U3?

5. Jan 21, 2016

### prishila

U2 will continue being equal to U3 and won't change.

6. Jan 21, 2016

### cnh1995

Right. Hence, the remaining bulbs continue to light.

7. Jan 21, 2016

### Algr

The lights are connected in parallel, so power doesn't need to go through one bulb in order to get to the others. It's like ties on a railroad track - you can remove one tie, and the others still touch both sides of the track.

The exception to this is strings of lights for a christmas tree. These are too small to individually accept 120/240 volts, and so are usually connected in series to reduce voltage.

8. Jan 21, 2016

### CWatters

The voltage on bulb 2 is the same but the current doesn't increase.

Remember Ohms law says V=IR so

I=V/R

The voltage stays the same, what about the resistance?