Here's a circuit with two resistors. The voltage is still about 5v.

 But if you place the alligator clips in a way that lets you measure the total resistance, you see that there is about a 50% drop in voltage.

 Here we set up a speaker system that would play a tone on equal intervals. The potentiometer allowed us to pitch-shift the tone by changing the analog input value.

The same speaker system with a photoresistor added in allowed us to change the pitch by shifting the light as well as turning the knob on the potentiometer.