Lab: Tone Output Using An Arduino

https://player.vimeo.com/video/463370355

I used photocells as variable resistors to instead the FSRs for the lab, and wire clips to connect a speaker to my breadboard.

However, what I actually tried at first was to use 2 potentiometers instead of FSRs as right image:

I also placed a 10kΩ resistor at the junction of the two branch circuits of the potentiometers to avoid short circuits. After checking the sensor input range, I got a range very similar to the example. However, when I uploaded the final code to the Arduino, nothing happened... The speaker kept humming and its frequency didn't vary when I turned the knob.

Questions:

1. Why potentiometers didn't work in this case? I thought it should be a range problem, but values in the serial monitor were normal when I checked before.
2. What's the difference between photocells and phototransistors? Google told me that phototransistors change their conductance, while photocells change their resistance depending on the intensity of the light falling on them. But changes in conductance will also lead to changes in resistance (right?), so why can't we use phototransistors to conduct this lab?

https://player.vimeo.com/video/463370224

This part is so much fun, though it's kind of complicated to understand the comprehensive programming.

Lab: Servo Motor Control with an Arduino

I directly used male-male jumping wires to connect the servo motor and the breadboard. I think this is exactly the same as our course pages.

Question:

If I have these wires, I don't need to connect the header pins to the servo motor connector, right?