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Registered Member #2063
Joined: Sat Apr 04 2009, 03:16PM
Location: Toronto
Posts: 352
take a look at question 15 part c) yeah i'd like to see what happens if you stick 100,000,000,000,000,000,000 volts into an op-amp on thing for sure, it won't output 25v ;)
Registered Member #1451
Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661
Are you commenting on how the equation doesn't put a limit on the input or output? They are assuming an ideal op-amp in an attempt to relate math to real life.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
... as well as confusing the students as to the way the term "op-amp" is used today. Once upon a time, when valves were replacing wheels, shafts and discs in analogue computers, operational amplifiers were modules that performed "an operation", so your analogue computer might contain adders, gain blocks, logging amplifiers, to be patched together with 1/4" jack leads.
These days of course, an "op-amp" is just an amplifier with huge gain intended to be tamed with some sort of feedback, and the function they describe would tend to be called a log-amp.
The input may need to be in the order of 10^20 volts, but log() is not well defined. It could be log10, but loge or ln is another possibility. Even if it was log2, the input would still be a bit large for an op-amp (for large values of "a bit").
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040
Dr. Slack wrote ...
... as well as confusing the students as to the way the term "op-amp" is used today. Once upon a time, when valves were replacing wheels, shafts and discs in analogue computers, operational amplifiers were modules that performed "an operation", so your analogue computer might contain adders, gain blocks, logging amplifiers, to be patched together with 1/4" jack leads.
These days of course, an "op-amp" is just an amplifier with huge gain intended to be tamed with some sort of feedback, and the function they describe would tend to be called a log-amp.
The input may need to be in the order of 10^20 volts, but log() is not well defined. It could be log10, but loge or ln is another possibility. Even if it was log2, the input would still be a bit large for an op-amp (for large values of "a bit").
mathematical convention is to assume that log x = log [base 10] of x unless a different base is denoted (log base e of x has a special form, "ln x," which is used whenever it is "e")
Registered Member #49
Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362
DaJJHman wrote ...
Dr. Slack wrote ...
... as well as confusing the students as to the way the term "op-amp" is used today. Once upon a time, when valves were replacing wheels, shafts and discs in analogue computers, operational amplifiers were modules that performed "an operation", so your analogue computer might contain adders, gain blocks, logging amplifiers, to be patched together with 1/4" jack leads.
These days of course, an "op-amp" is just an amplifier with huge gain intended to be tamed with some sort of feedback, and the function they describe would tend to be called a log-amp.
The input may need to be in the order of 10^20 volts, but log() is not well defined. It could be log10, but loge or ln is another possibility. Even if it was log2, the input would still be a bit large for an op-amp (for large values of "a bit").
mathematical convention is to assume that log x = log [base 10] of x unless a different base is denoted (log base e of x has a special form, "ln x," which is used whenever it is "e")
-Jimmy
This seems to apply in math education but many other fields disagree. I recall a number of physics texts where log is assumed to be natural log. Several computer algebra systems or scripting languages (e.g. matlab) define "log()" as natural log; base ten log is "log10()."
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Math text book fail.......again
