equations

EQUATIONS

Equations are frequently used in electronics.

For example take the following (which is Ohm's Law).

V = I x R

Where V = voltage measured in Volts, I = current in Amps and R is resistance in Ohms.

So if we know the current and resistance in a circuit we can find the voltage by multiplying the current by resistance.

For example if the current is 10 amps and the resistance is 2 ohms the the voltage is

10 x 2 = 20 volts

Since the values on both sides of an equation must be equal, if we do something to one side we must do the same to the other side.

Taking the same equation.

So if we multiply the L.H. by 2 we do it to the R.H. side as well.

2 x I x R = 2 x V

2 x 10 x 2 = 2 x 20 = 40

V + 3 = (I x R) + 3

Incidentally, instead writing I x R it is the custom to write IR without the multiply sign which can be confused with the letter x.

V = IR

If we divide a value by itself such as I/I in an equation then that value disappears from the equation.

Taking our first equation and dividing both sides by I.

The two I's on the right disappear and we are left with

We have made R the SUBJECT of the equation instead of V.

We call this process THE TRANSPOSITION OF FORMULA.

Now if we know the values of voltage and current in the equation then we can calculate the resistance.

If the voltage is 20 volts and the current is 10 amps, then the resistance is 2 ohms.

If we divide both sides of the original equation by R, then R disappears from the R.H. and appears on the L.H.

We have made I the subject of the equation.

We can now calculate I if we know V and R.

V = 20, R = 2, then I = 10 amps.

We now have Ohm's Law in three forms.

Knowing any two values we can find the third.

Watts = Volts x Amps

W = VI

Now find the other two equations by transformation, making V the subject in one, and I the subject in the other.