# Incandescent lamps

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#### skittleslove

##### Member
An incandescent had operated on a 120 volt circute for 8 hours a day 5 days and 9.6 kilowatt-hours of electrcity. What was the resistance of the lamp?

#### charlie

##### Senior Member
Re: Incandescent lamps

I'll bet your instructor would rather you do the work yourself.

#### bjohnson

##### Member
Re: Incandescent lamps

Oops...good point....sorry post deleted.

[ February 28, 2003, 09:52 AM: Message edited by: bjohnson ]

#### bphgravity

##### Senior Member
Re: Incandescent lamps

Try determining what wattage of lamp would produce 9,600 watts over that period of time, and then apply Ohm's Law to get R.

#### mikeames

##### Senior Member
Re: Incandescent lamps

v= I*R

P= I*V

9.6 KWH = 9600 watt hours

Ill stop there.

#### landelectric

##### Member
Re: Incandescent lamps

CHEATER ! CHEATER ! CHEATER !

#### tim

##### Senior Member
Re: Incandescent lamps

Maybe I'm wrong but here goes anyway. As a residential electrician why would you even need to know the answer to a question like that? For you commercial and industrial guys, Is there a situation where you need information like this?After 20 some odd years, I've never wondered what the resistance of a light bulb was. :roll:

#### russ

##### Senior Member
Re: Incandescent lamps

Tim:

If you work for someone else, you could get by with out any calculations or even opening a code book. That said you still have to know your trade. When licenses or certifications are required there has to be someway to justify issuance. Other wise why require them.

Russ

#### tim

##### Senior Member
Re: Incandescent lamps

Russ, I work for myself and with my father. I have an electrical liscence in 5 jurisdictions. I still wonder why and where I would need to know the resistance of a light bulb in residential settings. Like I stated above, maybe there is a reason to know in an industrial or comercial setting that I don't know about. Thats why I asked. Also by the way, I use the code book and do calculations just about every day!!

#### mikeames

##### Senior Member
Re: Incandescent lamps

Its not the issue of knowing the resistance of a fillament in a bulb. It knowing the principles and understanding why so you can calculate and understand more important and related areas of our trade. Learning to think backwards.

#### roger

##### Moderator
Staff member
Re: Incandescent lamps

Mike, I agree. I think most like to know how and why in any situation.

I know some will change a spark plug in an internal combustion engine and be happy that it runs better, but myself, as well as many, have the need to understand the way the engine works and why the plugs are needed.

Roger

#### luke warmwater

##### Senior Member
Re: Incandescent lamps

I've always liked math. In school I took algebra, geometry ,trig., calculus. My father always said, "the only people who need to know that are the people who teach it."
Tim, I agree that you will probably never need to know the resistance of a light bulb filiment, but I also have to agree with Mike. I, as well as others I'm sure, just like to know the theory.

#### winnr1

##### Member
Re: Incandescent lamps

60 ohms

#### skittleslove

##### Member
Re: Incandescent lamps

The reason i asked this question is because my Instuctor has asked use to use all of our resorces to help us with our final exam it is an open book test but i could not find how to figure this question out so i asked for help here. I am just starting out in this field, i am a senior in high school. I thank everyone who has helped me. And I like the coments from the others.

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