rjmockster
Member
Okay, I remember the E, I, and R formula according to Ohm's law, but can some one remind me of the Watt formula? I know E x I = W, but how do I figure resistance from 100 watts and 120 volts?
Basic theory/formula's
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charlie
Senior Member
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- Indianapolis
Re: Basic theory/formula's
Don't forget that you can substitute from E=IR to P=IE and vice-versa. An example would be to substitute for E, P=I(IR) becomes P=I^2R.
Don't forget that you can substitute from E=IR to P=IE and vice-versa. An example would be to substitute for E, P=I(IR) becomes P=I^2R.
physis
Senior Member
Re: Basic theory/formula's
I find that an Ohm's law equation can always be solved by remembering one rule:
I x R = E can be changed to
E / R = I or
E / I = R
It might be clearer to use numbers:
2 X 3 = 6 can be changed to
6 / 3 = 2 or
6 / 2 = 3
Given any two variables the third can always be deduced. I also think of this as being able to "unmultiply" something by dividing it in the opposite direction.
100w / 120v = .833333A and you need resistance
that's E / I = R or 120v / .833333A = 144ohms
[ May 09, 2003, 03:54 PM: Message edited by: physis ]
I find that an Ohm's law equation can always be solved by remembering one rule:
I x R = E can be changed to
E / R = I or
E / I = R
It might be clearer to use numbers:
2 X 3 = 6 can be changed to
6 / 3 = 2 or
6 / 2 = 3
Given any two variables the third can always be deduced. I also think of this as being able to "unmultiply" something by dividing it in the opposite direction.
100w / 120v = .833333A and you need resistance
that's E / I = R or 120v / .833333A = 144ohms
[ May 09, 2003, 03:54 PM: Message edited by: physis ]
jmc
Member
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- Massachusetts
Re: Basic theory/formula's
Watts = volts x amperes, P = E x I. however, this is only where you have a purely resistive load or unity power factor, no inductive loads. Where inductive loads are supplied, watts = volts x amperes x power factor, P = E x I x PF.
Watts = volts x amperes, P = E x I. however, this is only where you have a purely resistive load or unity power factor, no inductive loads. Where inductive loads are supplied, watts = volts x amperes x power factor, P = E x I x PF.
bphgravity
Senior Member
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- Florida
Re: Basic theory/formula's
DOCTOR WATTS pocket guide is pretty good too by Mark Shapiro.
DOCTOR WATTS pocket guide is pretty good too by Mark Shapiro.
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