UNIVERSITY OF MASSACHUSETTS DARTMOUTH
COLLEGE OF ENGINEERING
EGR 101 INTRODUCTION TO ENGINEERING I
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This assignment is due Thursday, October 23, 2013.
Use engineering paper.
Show all of your steps.
Present your work neatly and clearly.
Box your final answers.
Problem 1
Consider the following circuit that consists of series and parallel capacitors. Each
capacitor has capacitance equal to 0.047  F
 Find the total capacitance CT in  F .
Problem 2
Consider the following circuit in which R1  R2  5M  and each capacitor has
capacitance equal to 12 pF.
 Draw a simple circuit with one total resistor and one total capacitor, and label
their values with proper units.
 Find the time constant in ms.
Problem 3
Consider a capacitor with a plate area equal to 900cm 2 . The plate spacing is 0.01 mm.
The design requires a capacitance of 923.9 nF. In order to select the dielectric material,
calculate the following:
 The material permittivity  in F/m, and
 The material relative permittivity  r .
 What material do you select from Table 12.1 on p. 368 based on your relative
permittivity?
 By what factor should you increase or decrease the capacitor spacing if the
capacitor is 923.9 pF instead of 923.9 nF?
Problem 4
Consider the following circuit in which the SPDT switch is set to discharge the capacitor
and has been closed for a long time. The capacitor is 10 F and R2  1k  .
 Use Ohm’s law to find R3 in order to limit the initial discharge current to 5 mA.
 Report in ms the time constant of the circuit in the discharge mode.
In the discharge mode, the voltage across the capacitor is given by
vC  t   VS e

t
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where   RC .
 Find an expression for the current as a function of time, i  t  .
 Plot i  t  in the interval t  0 using Excel with a time interval equal to 5 103 s
and fill in the first 25 rows.
a. Submit a copy of the graph.
b. Submit a print of the table that consists of two columns: the left column
containing time and the right column containing current values.