I have a 10k rotary potentiometer which turns from 0° to 270°. I wire it to an Arduino with the middle pin (2) connected to an analog input (A0) and the other two pins (1 and 3) connected to 5V and GND.
I know the potentiometer is a voltage divider between pin 1, 2 and 3 as above so as expected I get 5 volts on pin 2 when the potentiometer is turned left (0°), 0 volts when the potentiometer is turned right (270°) and something in between in the middle. The problem comes when I try to calculate the angle - voltage function. I expected that it would be a linear function that can be calculated from the two given points (0°, 5V) and (270°, 0V) but when I turn the potentiometer to 135° which is supposed to be the middle point I don't get 2.5 volts instead I get something around 1.5 volts. I also noticed that when close to 270° a single ° in rotation corresponds to a bigger voltage change than when closer to 0°. So is this normal or is my potentiometer busted? And if it is normal why is it so?
I did some measurements and came up with the table below as Umar suggested
Degrees | Ohms | Delta 0° | 3 | - 45° | 480 | 480 90° | 972 | 492 135° | 1704 | 732 180° | 3423 | 1719 225° | 7280 | 3857 270° | 10300 | 3020
So Kevin White is correct it seems that I have a tapered audio potentiometer and the function is logarithmic (the blue curve in Kevin's answer). Thanks, everybody for your time and effort.