You're talking about an electronscope, not a microscope! An electronscope is a device used to detect and measure static electricity, not to magnify objects.

Here's how the replacement of the metal knob with a plastic one would affect an electronscope:

* Conductivity: Metal is a good conductor of electricity, while plastic is an insulator. Replacing the metal knob with a plastic one would reduce the electronscope's sensitivity to static electricity.

* Charging: The metal knob would readily acquire and discharge static charges, allowing the electronscope to detect even small changes in electrical potential. The plastic knob would be less likely to acquire or discharge static charges, making it harder for the electronscope to respond to static electricity.

In summary: Replacing the metal knob with a plastic knob would make the electronscope less sensitive and less responsive to static electricity.

Let me know if you have any more questions!