Answer:
point-contact transistors
In an electric circuit, the free electrons are moving around. Since equal charges repel and opposite charges attract, the electrons move from the negatively charged to the positively charged pole of the voltage source.
<em>in Scientific method observation comes first,,,
hypothesis is a short time theory made on the basis of observation..
hypothesis depends upon observation...
you suggest any statement about the phenomenon that you felt either my your mind or senses that is hypothesis...</em>
Frequency = (speed) / (wavelength) = 20 / 0.5 = 40 per second = 40 Hz.