Problem Set 1 (due 2/23/06)
CH332 (SP ’06)
1. Identify the four main components (as discussed in class) of the following
instruments. What is the domain of the analytical and the transduced signal?
a) mechanical balance
b) digital analytical balance
c) quartz crystal microbalance (QCM)
d) 0.1o mercury thermometer
e) thermocouple
f) infrared (IR) digital thermometer
What are the relative merits of these instruments which are used to measure the same
physical variables? What factors might be considered in selecting one over another
for a given application?
2. Why is it important that a good voltage measuring device (like the DMMs you use in
lab) has a high internal resistance? What is the minimum internal resistance of a
voltmeter necessary to accurately measure the output from a voltage divider with R1 =
R2 = 100 Ω to within 0.5% error? From a divider with R1 = R2 = 10 MΩ? Which of
the above dividers would you choose for a generic load of unknown resistance?
3. Answer Skoog problem 2-5 for the following resistor values: R1= 10 Ω, R2= 25 Ω,
R3= 15 Ω, R4= 50 Ω .
4. A current of 1 mA charges a 1µF capacitor. How long does it take the ramp to reach
10 V? Disconnect the current source. How long would it take to discharge the
capacitor to 1% of its initial charge through a) a 10 kΩ resistor, and b) a 10 MΩ
resistor?
5. The following Op-Amp circuit can act as a current source for a load resistance. What
values of R1, R2, R3 and V+ could you use to source 1mA of current through the
load?
V+
R1
+
-
R2
R3
load
6. Design a circuit to perform each of the following functions. Use any number or
combination of OP-AMPs, capacitors and resistors necessary.
a) Photomultiplier tubes are transducers that convert incident light into a current
signal. They characteristically have a small “dark current” produced even in the
absence of light. Design a circuit to convert the output of a photomultiplier tube
to a voltage and correct for the dark current baseline.
b) Correct for a baseline and integrate the area under a spectroscopic peak
c) Take the difference of two voltages (from a sample and reference signal) and
amplify the difference by a factor of 50.
7. For the following circuit with a time-dependent input signal, sketch the frequency
dependence of Vout/Vin for C= 0.1 µF, R1= 1 kΩ and R2= 1 kΩ (indicate f3dB). Now
replace with R2= 10 kΩ. What is the advantage of using such a circuit for filtering?
C
Vin
R1
+
R2
Vout
8. I’d like to know more about the background and interests of everyone in CH332. List
all Chemistry courses and other related courses in the sciences you’ve taken at Colby
(or elsewhere). Additionally, describe any research work you’ve done that involved
the use of instruments. Indicate the instrumental techniques you’ve encountered and
your degree of familiarity with each. Is there a technique that you have become
particularly proficient with? Is there any technique that you have used or expect to
use in the future that you are interested in exploring in detail?