# Homework Help: Simple Power/Energy Question

1. Jan 3, 2006

### saschouch

Now, I think i know how to do this one, but I'm just not sure if I'm using the correct figures. To figure out how much it would cost to run an appliance for a certain amount of time per month, you would need to know the wattage of the appliance, correct? Does voltage need to be known? For example, a guitar amplifier puts out 120 Watts, and is 250 Volts. I tried to use just the wattage, converted to kW, and multiply by 3600 to get kW/hrs. For some reason, I got outrageous numbers for the amount of $it costs. Can anybody tell me what I'm doing wrong? By the way, power costs$.075 per kW/hr.

2. Jan 3, 2006

### dicerandom

You also need to divide the wattage by 1000 so that you have kilowatts. The voltage doesn't matter, it's already been taken account of in the calculation of the wattage.

As an aside, often devices are labeled with what their maximum power consumption is, i.e. your amp won't be sucking up a full 120 watts if it's just sitting there with the power on but you're not playing anything on your guitar.

4. Jan 3, 2006

### dicerandom

See my second edit, you should be multiplying by hours and not seconds.

5. Jan 3, 2006

### saschouch

yes! Thanks a ton!