# Current and Watts

1. Jul 15, 2011

### gkangelexa

Can you determine current given only the watts?

Ex) if you have a lightbulb with 120 Watts, can you determine the current (charge) that flows through it in a second, for example?

2. Jul 15, 2011

### sophiecentaur

Nope.
In a low voltage circuit, you need a lot of current to produce the same power as for a high voltage circuit.
Remember - Power (Watts) = Volts (Volts) X Current (Amps)

3. Jul 15, 2011

### potatoecannon

From the way the question is phrased, no was the correct answer.
You need any 2 (Voltage/Current/Resistance/Power) to determine an unknown in basic circuits.

However, if you MEANT (since you referenced a 120W light bulb) how much current will the bulb draw on a standard 120 VAC circuit, then that is simply P=V*I ---> I = P/V = 120W/120V = 1 Amp.

A 120 W rated bulb will not actually draw/dissipate 120 W of power unless it is powered by the expected voltage (ie a 12V battery will not push 10 amps through it).

4. Jul 15, 2011

### jambaugh

In general no, you need also voltage:
Power = voltage times current.

In the lightbulb example you probably know the voltage implicitly i.e. it's a lightbulb used with 120V AC house lights. In that case you would solve to find the current is 1 amp (1 coulomb per second).

current = power / voltage