### F.A.Q's:Quantum Mechanics

1. How should we think about quantum mechanics?  For example, what is meant by a "measurement" in quantum mechanics?  Does "wavefunction collapse" actually happen as a physical process?  If so, how, and under what conditions?  If not, what happens instead?
Many physicists think these issues are settled, at least for most practical purposes.  However, some still think the last word has not been heard.  Asking about this topic in a roomful of physicists is the best way to start an argument, unless they all say "Oh no, not that again!".  There are many books to read on this subject, but most of them disagree.
2. Can we build a working quantum computer big enough to do things ordinary computers can't easily do?
This question is to some extent impacted by the previous one, but it also has a strong engineering aspect to it.  Some physicists think quantum computers are impossible in principle; more think they are possible in principle, but are still unsure if they will ever be practical.Here are some ways to learn more about quantum computation:
• John Preskill, course notes on quantum computation.
• Michael A. Nielsen and Isaac L. Chuang, Quantum Computation and Quantum Information, Cambridge U. Press, Cambridge, 2000.  Errata, table of contents and Chapter 1 available here.

### COMMON COLLECTOR CONFIGURATION OF A TRANSISTOR

COMMON COLLECTOR CONNECTION

In  this  configuration  the  input  is  applied  between the  base  and  the  collector and  the  output  is  taken  from  the  collector  and  the  emitter.  Here  the  collector  is common to both the input and the output circuits as shown in Fig.

Common Collector Transistor Circuit

In  common  collector  configuration  the  input  current  is  the  base current  IB  and  the output current is the emitter current IE. The ratio of change in emitter current to the  change in the base current is called current amplification factor.

It is represented by

COMMON COLLECTOR CIRCUIT

A test  circuit  for determining the  static characteristic  of an NPN transistor is shown in Fig. In this circuit the collector is common to both the input and the output circuits.   To   measure   the   base   and   the   emitter   currents,   milli   ammeters   are connected in series with the base and the emitter circuits. Voltmeters are connected   across the input an…