- #1

yakabod

What is the shortcut on solving problems that deal with ohms law?

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- Thread starter yakabod
- Start date

- #1

yakabod

What is the shortcut on solving problems that deal with ohms law?

- #2

Tom Mattson

Staff Emeritus

Science Advisor

Gold Member

- 5,549

- 8

You'll have to be more specific.

- #3

Dx

E

------

I | R

Here is a pyramid so if you want to solve for eg; E = IR. Just cover up what you want to solve for and the remaining letters left are your formulas. Another eg; I = E/R. Is that what you mean, sir? Does that help?

Dx

------

I | R

Here is a pyramid so if you want to solve for eg; E = IR. Just cover up what you want to solve for and the remaining letters left are your formulas. Another eg; I = E/R. Is that what you mean, sir? Does that help?

Dx

Last edited by a moderator:

- #4

yakabod

used these kind of formulas:

resistance = voltage/current

and

current = voltage/resistance

now i was asking if there was easier shortcuts on solving these.

now looking at the last problem i am stuck. instead of asking for ohms or amps it asked find the current of a watt.

Code:

`calculate the current in a 140-w electric blanket connected to a 120-v outlet`

now my question is how to solve that with a diffrent formula? what formula is this?

- #5

Tom Mattson

Staff Emeritus

Science Advisor

Gold Member

- 5,549

- 8

Originally posted by yakabod

now i was asking if there was easier shortcuts on solving these.

That's not short enough for you? [?]

calculate the current in a 140-w electric blanket connected to a 120-v outlet

You need to learn basic units, and you need to start reading your book. I am not going to tell you the formula, because that gives away the whole thing. I am going to ask you a couple of questions that will lead you to the answer.

1. What quantity is measured in Watts?

2. Is there a formula in your book that relates the quantity in #1 to current (answer: YES, there is).

- #6

- 39

- 0

The pyramid is "V" on top, with "I" and "R" on the bottom. It can be expressed as three complimentary equations:

1)

2)

3)

Any time you have two of the factors from one side of the equation, you will know the third factor (the other side). In your question "calculate the current in a 140-w electric blanket connected to a 120-v outlet", you have

Now you need to figure out what the "Watts" means. Watts is volts*amps. Again, you can draw a pyramid to help remember it all. Put Watts at the top, and across the bottom you have volts and amps (amps being current). Again, this allows three expressions:

1)

2)

3)

Now, Watts is voltage*amps. Since you know the Watts and voltage, you can divide Watts by voltage to get current. 140/120 = 1.15 Amps, roughly.

Now you have two factors necessary for working with Ohm's Law. You have the voltage (120) and the current (1.15).

Watts = voltage*amps.

You've got voltage and watts:

So, by re-arranging the factors you can get:

Simply fill in the "?".

Last edited:

- #7

Dx

remember P=IE, my friend.

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