How do i derive the formula for "E" in terms of P & R using the equations E= I x R & P= I x E

Expert Answers
violy eNotes educator| Certified Educator

Solve for I on P = I x E. 

Since, E is being multiplied on right side, we divide both sides by E. 

`(P/E) = (I x E)/E`

Cancel common factor on top and bottom of right side.

`P/E = I` or `I = P/E` 

Replace the I on E = I x R by what we got. 

`E = (P/E) x R`

Multiply both sides by E. 

`E x E = E x (P/E)x R` 

`E^(2) = P x R`

Take the square root of both sides. 

`E = sqrt(P x R)`


pramodpandey | Student

Eliminate I from both equation (only I prsent in both equation)

since  `E=IxxR`

`E/R=I`                  (i)



`P/E=I`                   (ii)

from (i) and (ii) ,we have


cross multiply


which is required formula.