Pardon me, I'm a total newb to electronics. My question is, when a device is measured in watts, such as a 60-watt light bulb, is this ALWAYS supposed to be assumed to be watt-hours, i.e. 60 watts per hour?
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Energy is an amount, while power is a rate at which energy is used.
Watt-hours are like buckets, and watts are like buckets per hour. If you have 5 buckets of energy and you pour one bucket per hour, you'll be able to pour for 5 hours before you run out. If you turn on a 60-watt light bulb for 1 hour, you have used 60 watt-hours of energy. If you use it for 2 hours, you have used 120 watt-hours of energy. If you turn it on for only 1 minute, you have used 1 watt-hour. It's a little confusing since the "per hour" is inside the term "watt", so to make the rate into an amount, you need to multiply by a time unit to cancel it out. It would be a lot more intuitive if we worked in kilojoules and kilojoules per hour. :) |
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One point not yet mentioned: a 60 watt bulb will use 60 watt-hours per hour, or 60 watt-seconds per second, or 60 watt-microseconds per microsecond, or 60 watt-centuries per century. In other words, the "watts" part of the bulb's power usage has nothing to do with hours or any other unit of time. |
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Stimpy, the power rating tells you the rate at which the device consumes energy. So yes, a 60-Watt bulb will consume 60W*h or 0.06kWh of electricity in one hour. Watt-hours measure energy consumption. There is a simple little page here that shows some calculations. I would also strongly recommend reading the HyperPhysics box on Work, Energy, and Power, and especially the links on the Power Concepts page. |
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You are correct in assuming a 60 watt device will consume 60 watt-hours in one hour, but the former (power) is a rate, the latter is an amount (energy). |
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The concept of 'Watt-hours' as Watt x Hours will be confusing to someone who cannot conceptualize Watt - being 'enegergy used per amount of time'. I sometimes try to explain this using more familiar concepts: If we use the term 'Keem' in stead of 'km/hour', one could use 'Keem-Hour' to describe distance travelled - going 60 Keem for half an hour means you've travelled 30km as 60 x 0.5=30 Just like a rental company that's interested in the distance your travelled in their car, the energy company is interested in the energy used - they will charge you per Watt-hour. If a Watt-hour costs 1c, it will cost you 60c if you leave a 60 Watt lamp on for one hour. |
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