I was learning about voltage dividers from here, and I decided to try a test circuit with my Radioshack learning lab. With an input voltage of 4.5V and two 1000Ω resistors, I expected the voltage output would be 4.5*(1000/(1000+1000)) = 2.25V.
After looking at this, I thought that the only way to measure the voltage output from the divider was to measure the voltage drop of a resistor (otherwise I'd just get a 0V reading), so I added a 1000Ω resistor to the circuit (R3 in the drawing below). I measured the voltage across this extra resistor, but I got 1.48V for an output voltage. What I found odd was that when I used higher-resistance resistors, the voltage drop output got closer and closer to 2.25 V (the highest I did, 1MΩ, led to the 2.25V reading I wanted).
Can I use resistors like this R3 to test the voltage output coming out of this voltage divider? If not, how can I check by measurement that this voltage divider gives an output of what I'm sure is 2.25V?