# Voltage devider

#### fury

Joined Sep 22, 2011
4
Hi, folks. ... this my first post.
Im new in electrical circuits, so i have dummy question about voltage divider. I really can't managet to do this example from socratic project:

http://www.ibiblio.org/kuphaldt/socratic/output/e_divide.pdf problem 15.

If the both resistors are in series - no problem i will use $$Vout = Vin \frac{mR1}{R1+R2}$$ But if they are in parallel i try with formula $$Vout = Vin\frac{mR1R2}{R1+R2}$$ and nothing - rong answer. So i need help for that!

Thanks !

#### mrmount

Joined Dec 5, 2007
59
If the resistors are in parallel they will have the same voltage across them.

Joined Dec 26, 2010
2,148
Question 15 - the 5kΩ potentiometer.

For the 0% and 100% settings the answer should be obvious, but for each of the other settings redraw the pot as a two-resistor divider.

The resistance to ground will be the given percentage of the total, and the resistance to supply will be the total minus the resistance to ground.

Now calculate the effective value of the resistance to ground by working out the parallel combination with the 1kΩ.

Finally work out the modified division ratio, multiply by the input voltage, and you will have the answer.