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PHYS-104 – FUND. OF PHYSICS, II
UNIT II (B)
ELECTRIC ENERGY and CAPACITANCE
Objectives:
A.
Using the concept of potential difference and potential
energy of charges, be able to:
(N)
1.
(N)
2.
(N)
3.
(E)
4.
(E)
5.
(E)
6.
(E)
7.
(E)
8.
(E)
*9.
(N)
B.
(N = No Equation Sheet; E = Equation Sheet)
define it between two points using a test charge and
apply to explain a physical situation, i.e.,
cathode-ray tube, cell membrane action potential,
lightning bolts, sign of charges knowing potential
energy charge, etc.
solve for one variable in terms of the other two
(using proper units) involving potential difference,
electric field strength and separation distance.
state what physically occurs near equipotential
surfaces and draw in equipotential lines near
charged bodies.
correctly solve problems involving the potential
difference between parallel plates, separation
distance, and force on a given charge between the
plates.
solve for any variable such as work done in terms of
the:
(a) charge, electric field strength, and separation
distance.
(b) charge and voltage.
explain what is meant by "batteries are a source of
potential difference" and apply to practical
examples.
discuss, using physical principles, the outcome
involving electric fields and potential difference,
i.e., if V = O at a point, must E = O as well?
solve for the power needed to pump ions at a given
rate against a given potential difference.
solve for the number of electrons reaching a CRT
screen given accelerating potential and power
rating.
For a given moving charge, solve for the:
1.
2.
acceleration given the mass, charge, electrode
distance, and potential difference of the field.
kinetic energy in electron volts and joules, mass,
or speed if given the other variables.
Phys104, OBJ, Unit IIB Sp13
- 2 (N)
C.
In relation to capacitance, be able to identify:
1.
2.
3.
4.
D.
For capacitors be able to solve for:
(E)
1.
(N)
2.
(E)
3.
*4.
E.
what a capacitor does and the physical principles of
its operation in electrical circuits.
the effect on capacitance for different dielectrics
(especially how they affect the electric field),
separation distances and plate area for parallelplate capacitors.
practical examples of capacitors.
relate dielectric constant, C, Q and V to a parallel
plate capacitor and apply to explain a practical
situation.
the capacitance, dielectric constant, separation
distance and/or area of parallel plate capacitors in
terms of the other variables.
capacitance, charge or voltage in terms of the other
two given variables.
the energy, capacitance(charge), or voltage given
the other variables
the work required to pull the plates of a capacitor
to a multiple of their original separation.
Be able to solve for the:
(N)
1.
(E)
2.
equivalent capacitance of up to five capacitors in
series; in parallel.
charge across, the potential difference across, and
the energy stored across the equivalent capacitance
as well as across each capacitor in series and in
parallel circuits in (1).
LABORATORY OBJECTIVES
A.
For a given material, be able to classify it as a good
conductor, poor conductor, or non-conductor (insulator) and
discuss the physical principles involved to substantiate your
choice.
B.
Identify the quantities that charge and potential energy
depends upon, what makes charges move in a conductor, and
what happens to charges moving through conductors.
C.
Apply basic principles learned in Objectives A and B to
explain the results of a practical situation.
Phys104, OBJ, Unit IIB Sp13
- 3 D.
Be able to construct a capacitor out of aluminum foil and
plastic wrap and connect it to a signal generator and
loudspeaker circuit to:
1.
2.
identify the relation between frequency and impedance.
read an impedance vs frequency graph to answer questions
such as what is the frequency of a 5 ohm impedance, etc.
Phys104, OBJ, Unit IIB Sp13
- 4 LEARNING ACTIVITIES - ELECTRIC ENERGY
Read:
Textbooks:
College Physics,9thed.,Serway,Chapt 16(skim pp. 555-558, 560-562)
College Physics, 11th ed.(Schaum's Outline), pages 281-294 (pps
252-262 in 10th ed.)
Optional:
Conceptual Physics, pages 425-430 in 10th edition
(pages 428-433 in 9th edition) on reserve in Library.
Homework:
Chapter 16; MC Q’s 2, 9 & 11; Concept Q’s 1, 2, 4, 5, 6, & 10
Problems 1, 3(add What is the energy in eV?), 7,14, 15, 23*,
25(add What is the energy of the charged capacitor?), 33(add Find
the potential difference across each capacitor in (a) and (b)),
37*, 45, 51(add calculate the maximum charge on the plates and
energy stored in the capacitor in (b))& non-extra credit problems
Extra 1: Three capacitors whose capacitances are 5.0, 10.0 and
50 µF are connected in series across a 12.0 V battery. Find the
charge on each capacitor and the potential difference across each
Extra 2: The three capacitors in Extra 1 are connected in
parallel across the same battery. Find the charge on each
capacitor and the potential difference across each.
Answers to Selected Even-numbered Homework Problems:
(14)
-9.08 J
Extra 1:CT =3.12 µF, Q =37.5 µC, V5 =7.5 V, V10 =3.75 V, V50 =.75 V
Extra 2: CT =65 µF; Q5 =60 µC, Q10 =120µC, Q50 =600µC, V = 12 V
Audio-Visual Material:
Video:
Fields Around Point Charges (29 min)
Laboratory:
Fields and Eqipotentials
Charges In Motion - An Investigation of Transfer of Electric
Charges through Various Materials; Production of a Flow of
Electric Charges
Making a Capacitor
Phys104, OBJ, Unit IIB Sp13