Electronics: How Sand Learned to Amplify
From the pn junction to transistors, feedback and oscillators: how doped silicon rectifies, regulates, amplifies and keeps time.
Electronics · 50 questions
Try 3 questions
1. Adding a little phosphorus to pure silicon produces what kind of semiconductor?
- P-type, with extra free holes
- N-type, with extra free electrons
- An insulator with no carriers
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Answer: N-type, with extra free electrons
Phosphorus has five valence electrons; four bond with silicon and the fifth is easily freed to conduct.
2. Unlike a metal, why does pure silicon conduct better as it gets hotter?
- Heat melts its crystal bonds
- Heat makes its atoms vibrate less
- Heat frees more charge carriers
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Answer: Heat frees more charge carriers
Thermal energy breaks electrons loose across the bandgap, and the rise in carriers outweighs the extra scattering.
3. What does the depletion region of a pn junction contain?
- Fixed ions and almost no free carriers
- A dense cloud of mobile free electrons
- Metal atoms that drifted from the contacts
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Answer: Fixed ions and almost no free carriers
Electrons and holes near the junction recombine, leaving charged dopant ions whose field opposes further diffusion.
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