Download Review questions for ISU old book Word document

Grade 12 Physics Independent Study
REVIEW
Old Textbook
Special Relativity:
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Which two scientists set up an experiment in 1887 to eventually establish that the “ether”
and therefore an absolute reference frame, did not exist? Describe the device used to
perform the experiment and how it showed there was no ether.
b)
According to scientists before 1887, what properties did the so-called “ether” possess?
c)
Before 1887, what two reasons did scientists have for believing in an “ether”?
d)
In 1905, Einstein based his special theory of relativity on two postulates. State and
memorize these postulates in full.
A rocket car is moving at 100,000 km/s [E] with respect to the earth. As it moves, it shines its
headlight eastward moving directly toward a “light speed detector” fixed to the earth. What speed
does the detector display as the speed of the light coming from the rocket car’s headlight? If one
erroneously believed in an absolute reference frame such as the ether, what speed would be
expected for the detector to display? Answers ( 300,000 km/s, 400,000 km/s)
State and memorize the formulas for a) time dilation b) length contraction c) mass increase
d) interconvertibility of mass and energy e) relativistic kinetic energy
Identify the symbols
used for relativistic time, proper time, relativistic distance, proper length, rest mass, and relativistic
mass
Distinguish between proper time and relativistic time, proper length and relativistic length, and
relativistic mass and rest mass, rest energy, relativistic total energy and relativistic kinetic energy.
As measured from earth, a star X, which is not moving with respect to the earth, is 8.0 light years
away. Note that a ‘light year’ is actually a distance unit. A spaceship initially passes by the earth
moving at 0.95c with respect to the earth, moving toward star X. At that instant the pilot of the
spaceship starts her ship clock to mark the start of her journey to star X. When the ship arrives at
star X, the pilot stops the ship clock and notes that 2.63 years have elapsed.
What is the time duration of the spaceship’s trip as measured by an observer on the earth?
( Ans 8.4 years)
What distance in light years does the pilot measure from earth to star X ? two methods (Ans 2.5
light years)
If the pilot of the spaceship is 50 kg as measured on a balance in the spaceship, what would an
observer on earth measure the pilot’s mass to be?
(Ans 160 kg)
What is the pilot’s rest energy?
( Ans 4.5 X 1018 J)
According to an earth observer, what is the pilot’s relativistic total energy? (Ans `1.44 X 1019
Joules)
According to an earth observer, what is the pilot’s relativistic kinetic energy? (Ans 9.9 X 1018 J)
a)
Starting with Einstein’s two postulates, and using the diagrams on p 681 and 684, derive the time
dilation and length contraction formulas.
Electrical Force:
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State the equation and proportionality relationship for Coulomb’s law of electrical force. What is
the value of the proportionality constant?
What is the electrical force between charges of 5.0 X 10 -8 C and 1.0 X 10-7 C if they are 5.0
cm apart? (Ans 0.0182 N repulsive)
Two charges exert an electrical force of “K” Newtons on each other. If one charge is doubled, the
other charge is divided by three, and the distance is multiplied by 4, what is the magnitude of the
new electrical force? ( Ans (1/24)K N)
Two identical positive charges of magnitude +2C are 16 cm apart. A third charge of +3C is on the
right bisector of the first two charges with the angles 36.9 degrees as shown: Find the size of the
net electrical force on the +3 C charge? (Ans 6.5 X 1012 N)
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page#2
Define electric field. What is the basic formula in terms of electric force and charge? How are
electric field lines arranged near a) a positive charge b) a negative charge ? What do electric field
lines tell us? ( 2 things )
The electric field strength is 4 N/C [E]. What is the electrical force on a -5 C charge in this field?
(Ans 2 N [ W])
A -6 C charge experiences a 30 N [W] electrical force. What is the electrical field strength?
(Ans 5 N/C [E] )
What is the formula for determining the size of an electric field near a point charge?
A +2 C charge is 20 cm to the right of a –3C charge. What is the electric field on the line exactly
halfway between the two charges? (Ans 4.5 X 1012 N/C [L] )
Millikan’s experiment determined that all charge is an integral multiple of the elementary charge.
What is the value for this elementary charge? If a neutral atom gains 3 electrons, what is its
charge? (Answer 4.8 X 10-18 C)
It takes 4.2 X 10-3 J of energy to move a 1.2 X 10-6 C of charge against an electric field from one
point to another. What is the magnitude of the potential difference between the two points?
(Ans 3500 J/C or 3500 V)
What is special about the electric field between parallel plates? Derive the parallel plate equation
V=Ed starting with V=W/q.
Parallel plates are 5.0 mm apart and have a potential difference of 300 Volts between them. If a
+2C charge is between the plates, what is the magnitude of the electrical force on the charge?
(Answer 1.2 X 105 N)
A charge Q Coulombs is d meters from another charge q Coulombs. What is the equation for the
electrical potential energy of this two charge system?
In a Millikan-type experiment, two horizontal parallel plates are 2.5 cm apart. An oil drop of mass
1.5 X 10-15 kg remains at rest when the potential difference between the plates is 460 V with the
upper plate positive. How many excess or deficit electrons does the drop have? (Ans 5 excess)
An alpha particle of +2 elementary charges and mass 6.7 X 10 -27 kg can be given some speed by
placing it at rest on the positive side of a parallel plate apparatus. Ignoring any gravitational
effects, what speed does the particle have when it reaches the negative plate?
(Ans 4.4 X 105 m/s)
Electromagnetism:
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State the law of magnetic poles. Draw a diagram of the magnetic field lines around a bar magnet,
including direction arrows. What does the direction of a magnetic field line tell us? What does the
spacing of adjacent field lines tell us?
Where is the earth’s south magnetic pole? Explain the difference between magnetic declination
and magnetic inclination?
What are the 4 ferromagnetic materials? Explain how can these materials become magnetized
using ‘domain theory’ .
State Oersted’s basic principle of electromagnetism. Current is defined as the direction of
POSITIVE CHARGE FLOW. If a current in a long straight wire is coming
out of the page, how are the magnetic field lines arranged?
What is a solenoid? How can the direction of magnetic field lines inside a solenoid be
determined? How does magnetic permeability help us?
State and memorize the equation to determine the magnitude of the magnetic force on a charged
particle moving with speed v in a magnetic field B. How can the direction of the magnetic force
be determined if we know the direction of the velocity and direction of the magnetic field
strength?
What are the units of magnetic field?
A uniform magnetic field of 0.4 Tesla is coming out of this page and a single electron is moving
from the bottom of the page directly up the page along the plane of the page. The electron has a
speed of 3.0 X 108 m/s.
What is the magnitude in Newtons for the magnetic force on the electron?
(Ans 1.9 X 10-15 N)
What is the direction of the magnetic force? (Ans left)
page #3
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Explain why a magnetic force can never speed up a moving charge, only change its direction.
A constant magnetic field of 5 T acts 90 degrees to the current in a long, straight wire 4 m in
length. If the magnetic force on the wire is 2 N, what is the current in the wire? ( Ans 0.1A)
Explain what the mass spectrograph does, how it works and draw a diagram of its basic parts.
What force causes the charged ions to move in uniform circular motion? Derive the mass
spectrometer formula m=qB2r2/(2V) An 9.1 X 10-31 kg electron is accelerated in a mass
spectrometer using a voltage of 46 volts. It is sent into a magnetic field of .005 Tesla. Find the
radius of the circular path it follows. (Answer 4.6 mm)
What is the strength of the magnetic field 15 cm from a long straight conductor carrying a current
of 100A? (Answer 1.3 X 10-4 T)
What is the force between two parallel conductors 2.0 m long, carrying currents of 4A and 10 A
respectively, in the same direction, and that are 25 cm apart in a vacuum? Is it attractive or
repulsive? ANS (6.4 X 10-5 N attractive)
Summarize Maxwell’s 4 main ideas on electromagnetism in words.
State 5 properties of all electromagnetic waves.
State 8 types of waves in the electromagnetic spectrum. What do all electromagnetic waves have
in common with regard to speed in a vacuum?
QUANTUM NATURE OF LIGHT
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In the 1890’s, scientists were studying the radiation emitted by hot solids, and encountered a
problem, an “ultraviolet catastrophe”. What is the ultraviolet catastrophe and how die Planck’s
hypothesis resolve it?
What is the formula for Planck’s quantum? What is the value of ”h”?
State Einstein’s photoelectric equation, and state what each symbol stands for. In a few sentences,
summarize the main ideas in his photoelectric effect. What is a “photon”?
Calculate the energy of a photon of blue light with frequency of 6.67 X 10 14 Hz both in Joules and
in electron-volts. (Answer 4.42 X 10-19 J or 2.76 eV)
Calculate the wavelength, in nanometers, of a photon with 3.2 X 10 -19 J of energy. (Answer 622
nm)
Barium has a work function of 2.48 eV. What is the maximum kinetic energy of ejected electrons
if the metsl is illuminated with 450 nm light? (Answer 0.28 ev)
What is the Compton effect? Even though the photon has no mass, what is Compton’s equation
for the momentum of a photon?
What is the momentum of a photon with a frequency of 4.5 X 10 15 Hz? (Answer 9.9 X 10-27
kgm/s)
Explain these ideas: a) wave-particle duality b) de Broglie’s hypothesis and equation
What is the associated wavelength of an electron, mass 9.11 X 10-31 kg, moving at 50000 m/s?
(Answer 1.5 X 10-8 m)
MODELS OF THE ATOM:
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Other than coming up with the planetary model of the atom, what additional information was
obtained by Rutherford, Geiger, and Marsden in their experiments? (4 points)
Outline the differences between continuous, emission and absorption spectrum.
What did the Franck-Hertz experiment show?
An unknown atom has first and second excitation levels of 3.65 eV and 5.12 eV, respectively.
Determine the energy and wavelength of a photon found in the emission spectrum of the atom if
the atom is bombarbed with an electron of energy a) 3 eV b) 4.5 eV, and c) 6 eV
Answers (0,0,3.65 eV,341 nm,5.12 eV,1.47 eV,243nm,846 nm)
Derive E=(-2pi2mk2e4)/(n2h2) using Bohr’s quantum hypothesis.
Page #4
WAVES
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Derive and express Snell’s law ratio sin i / sin R in terms of wavelength and wavespeed.
A water wave with wavelength 30 cm and speed 40 m/s in deep water travels into shallow water
where the wavelength changes to 24 cm. What is the speed of the water waves in the shallow
water in m/s? (Answer 32 m/s)
Water waves travelling at a speed of 28 cm/s enter deeper water at an angle of incidence of 40
degrees. What is the speed in the deeper water in cm/s if the angle of refraction is 46 degrees?
( Answer 31 m/s)
What is diffraction/ Which model, particle or wave, correctly predicts the diffraction of light?
What two factors affect the diffraction of light, and how?
Review other assigned problems in this section.