Chapter 14, Sound
14.1 Producing a Sound Wave 1. When a sine wave is used to represent a sound wave, the crest corresponds to: a. rarefaction. b. condensation. c. point where molecules vibrate at a right angle to the direction of wave travel. d
Chapter 6, Momentum and Collisions
6.1 Momentum and Impulse 1. A valid unit for momentum is which of the following? a. kgm/s2 b. kg/m2 c. kgm/s d. Nm 2. The dimensional equivalent of the quantity impulse in terms of the fundamental quantities (m
Chapter 5, Energy
5.1 Work 1. The unit of work, joule, is dimensionally the same as: a. newton/second. b. newton/kilogram. c. newton-second. d. newton-meter. 2. Rupel pushes a box 5.00 m by applying a 25.0-N horizontal force. What work does she
Chapter 12, The Laws of Thermodynamics
12.1 Work in Thermodynamic Processes 1. The volume of an ideal gas changes from 0.40 to 0.55 m3 although its pressure remains constant at 50 000 Pa. What work is done on the system by its environment? a. 7
Reading chapter 20-1 to 20-3
Electric field and electric potential
Electric potential of point charges
When a force is conservative, there is a potential
energy associated wi
Excess charge on a conductor
Since excess charge on a
conductor is free to move, the
charges will move so that they are
as far apart as possible.
The excess charge on a conductor
resides on its outer surface.
Electric field and electrons in conductors
Equipotential surfaces & E field
Any surface, imaginary or
physical, with a constant
electric potential is called
Electric field points in the
direction of decreasing
Electric field lines are
perpendicular to t
System of point charges
The potential due to a system of charges can be
calculated from the superposition of the potentials
due to individual charges.
V = 0 at infinity
Reading chapter 19-6 to 19-7.
Charge by Induction
Faraday ice pail
of charge residing only on the outside of
Electric potential difference V is defined to be
The function V as a function of position is called electric potential or
Only differences in the potential are physically important (similar to
Reading chapter 20-5 to 20-6.
The storage of electrical energy
A capacitor is a device consisting of two
One conductor with charge Q, and the other with
charge -Q w
Where should you hide during lightning?
During lightning, electrons travel in lightning bolts
between clouds and Earth.
If a lightning bolt strikes a conductor, electrons would
quickly (in the order of nano seconds) move to the
surface, and E inside the
Gravitational potential energy analogy
The work done by the gravitational field is equal to the
decrease in the gravitational potential energy.
The work done by the electric field is equal to the
decrease in the electric potential energy.
Charge in a conducting shell 2
Define a closed surface
outside the metal shell.
enclosed is equal to the
positive charge in the
Charge at the center
E field due to hollow sphere
E due to a uniformly charged thin spherical s
Clicker question: 1
A single point charge is
placed at the center of
an imaginary cube that
has 20-cm-long edges.
The electric flux out of
one of the cubes sides
C. How much charge is
at the center?
The voltage between the
cathode and the screen of
an old-fashioned television
set is V=22kV. If we
assume a speed of zero for
an electron as it leaves the
cathode, what is its speed
just before it hits the screen?
V from a point charge
Potential vs. potential energy
The potential is characteristic of the electric field
only, independent of a test charge that may or may
not be placed in the field.
Potential energy is characteristic of the charge-field
system due to an interaction bet
Gausss law and charges in conductors
Consider any arbitrary gaussian surface that resides
completely inside a conductor.
E is zero everywhere on the gaussian surface.
The net flux through the gaussian surface is then also zero.
The charge enclosed by t
Electric potential energy
As a charge q0 moves a distance
d in the opposite direction of a
uniform electric field E, electric
field does work on the charge.
W = Fd = q0 Ed
The change in potential energy in
this process is
U = W = q0 Ed
An electron is projected with
an initial speed of
toward a proton that is fixed
in place. If the electron is
initially a great distance
away from the proton, at
what distance from the
proton is the speed of the
capacitor used in AM radios, in which the
overlapping area between the plates can be changed.
Q 0 A
Two sheets of aluminum foil have
the same area, a separation of
d=1.00mm, and a capacita
, E, and the shape of a conductor: 2
If r1 < r2 , 1 > 2 .
If 1 > 2 , E1 > E 2 since E =
Dielectric break down occurs where the radius of
curvature is the smallest.
If a conductor has a sharp point, dielectric
breakdown can occur at relatively low po
A storage capacitor on a
random access memory
(RAM) chip has a
capacitance of C=55fF. If
the capacitor is charged to
V= 5.3V, how many excess
electrons are on its negative
Parallel plate capacitor
A common capacitor geometry is the
The exact mechanism of how lightning initially forms is
Charges are separated into layers within the cloud,
creating a huge potential difference between the
lower part of the cloud and the ground.
The negative charge on
Charge inside a hollow conductor: 2
Regardless of how much charge there might be at the
outer surface, the smaller conductor is at a higher
potential than the larger conductor.
If the two were connected with a conducting wire, all
the charge on the sm
Equipotential surfaces for two charges
Equipotential surfaces and electric field lines for two
An infinite flat sheet of
charge has a uniform surface
charge density equal to
=3.50 C/m2. The
electric field due to an
Reading chapter 20-4.
Equipotential region and surface
Since E is zero everywhere inside a conductor:
The value of potential is the same throughout the conductor.
If multiple conductors are touching, they a
There is a capacitor under each key.
As you press a key, the spacing between the
capacitor plates change, increasing the
Q 0 A
In a condenser microphone, also called a capacitor
microphone or el
1.5 F capacitors connected in parallel are
charged to 400 volts.
Capacitors store energy and could be dangerous.
U = CV 2 = ( 4.5F ) ( 400V) = 3.6 10 5 J
material is called a
Dielectric breakdown occurs
when a material is ionized
in very high electric fields
and becomes a conductor.
The magnitude of the E
field for which dielectric
breakdown occurs in a
material is called the
dielectric strength of that