Download Student : MengZi Guo

Student : MengZi Guo
SPH4U Unit Test #1
Gravity, electric field and magnetic field .
Note: There are more than 10 MC questions and more than 2 short answer questions in both
tests . Therefore, these tests can be rearranged into more copies to serve students better .
The MC questions on both test are put in the same order since there are 20 MC questions, so
teachers can take out their best 10 questions to make another copy of the test.
Multiple Choice Questions
[20 marks]
Select the best answer for each of the following questions :
1.Gravity is an _______force.
A. Attractive
B. Universal
C. Mutual
D. None of these
E. All of above
2.Weight is a measure of_________.
A. your mass.
B. the gravitational attraction between you and the earth.
C. mechanical equilibrium
D. all of these
E. none of these
3. In which case would you have the largest mass of an object? If the object weighed 1 N on the
A. Jupiter
B. earth
Student : MengZi Guo
C. moon
4.The gravitational force between 1kg of iron and earth is ___________ 1kg of marshmallows
and earth
A.
B.
C.
D.
greater than
less than
the same as
None of the above
5. What is static electricity?
A. electricity produced by friction
B. the energy of motion
C. the path along which electrons flows
6. crossing the wires in an electromagnet can reduce its magnetism
A. true
B. false
7. Electric current passing through a wire produces __________
A. a permanent magnet
B. a magnetic field around the wire
C. a compass
D. geographic poles
8. like charges repel, unlike charge attract and force between two charges is F=
is a description of _______.
A.
B.
C.
D.
Electrostatic forces acting between charges
Electromagnetism between charges
Potential Energy between charges
EM field
9. Magnetic field lines are same as lines of force
A. True
B. False
Student : MengZi Guo
10. Alternating current changes the ______of the current flow.
A. direction
B. amount
C. strength
D. voltage
11. Magnetic field lines that curve away from each other show
A. where the magnetic field is strongest
B. a magnetic domain
C. repulsion
D. attraction
12. Magnetic field lines _______
A. never cross.
B. cross at the north pole.
C. cross at the south pole.
D. cross halfway between the poles.
13. Magnetic fields are created by ___________
A. magnetic field lines
B. potential energy of molecules
C. spinning neutrons
D. moving electric charges
14. Different electromagnetic waves travel through vacuum at different speed
A. .True
B. False
15. _________is the measure of the force of gravity on an object.
A. mass
B. weight
C. density
D. equation
16. Electric Field lines always come from positive to negative charges
A. true
Student : MengZi Guo
B. false
17. which of the following in the universe is conserved.
A. energy
B. charge
C. linear momentum , p=mv
D. angular momentum
E. all of above
F. none of these
18. If there is no test charge present to measure electric field, then electric field does not exist.
A. True
B. False
19. The ________around a positive charge points away from the charge, and decreases in
magnitude with distance r
A. Electricity
B. electric field
C. electric force
D. magnetic field
Short Answers
1.
a) Find the magnetic forces in following figures, JUSTIFY your answer : [3 marks each]
Student : MengZi Guo
For the first figure, the F =0 since sin(0)=sin(180)=0, there is no force if v and B are either parallel or
antiparallel
For the second figure, the force is maximum when v and B are perpendicular to each other since
sin(90)=1.
b) Three points are arranged in a uniform magnetic field. The magnetic field points into the
screen.
i.
The negative charge moves from point A toward B. what is the direction of magnetic
force on the particle? Justify [ 3 marks]
ANS : The direction of the force on the particle is to RIGHT. The cross product of the velocity with the
magnetic field is to the left and since the charge is negative the force is then to the right
ii.
A positive charged particle is located at point A and is stationary. what is the direction
of magnetic force on the particle? Justify
[3 marks]
ANS: The answer is zero since velocity is zero , therefore the force is also zero.
2. Find the net force on an electron due to two nearby protons, each at distance r away and 90
degrees apart. [4 marks]
ans :
Student : MengZi Guo
3. Jack has rubbed a balloon with wool to give it a charge of -1.0 x 10^-6 C. He then acquires a
plastic golf tube with a charge of 4.0 x 10^-6C at a given position. He holds the location of
charge on the plastic golf tube a distance of 50cm above the balloon. Determine the electrical
force of attraction between the golf tube and the balloon. [4 marks]
ans :
Q1 = -1.0 x 10^-6 C and Q2 = +4.0 x 10-6 C
d = 50.0 cm = 0.50 m
F = 0.144N
4. The normal hydrogen atom consists of a proton nucleus and an orbital electron, each carrying
the fundamental charge of magnitude e= 1.60 x 10^-19 C. Assuming that the orbit is circular and
the separation between the particles is 5.3x 10^-11 meters. Find :
a) the force of electrical attraction between the particle. [ 2 marks]
8.14 x 10^-8N
b) the gravitational force of attraction between them. [ 2 marks]
3.61 X 10 ^-47N
c) which force is greater? how many times ?. [ 2 marks]
Student : MengZi Guo
Electric force is greater, 2.25 x 10 ^-47 times greater.
Communication problem
When a charged particle is fired into and perpendicular to a uniform magnetic field, it moves
along a circular path until it escapes the field. Is this statement true or false, justify your answer
in full details. Use a diagram to support your explanation . Find the expression of radius of the
orbit and angular speed . [ 6 marks]
this statement is true. when a charged particle moves in a magnetic field it experiences a force
that is perpendicular to the velocity. since the force is perpendicular to the velocity, the charge d
particle experiences an acceleration that is perpendicular to the velocity. The magnitude of the
velocity does not change but the direction will change and produce a circular motion.
circular motion produces centripetal accerlation,
a= V^2/R, R is radius of orbit
Newton's second law gives us F=ma=m( v^2/R)=qvB
Thus, R=mv/qB
Angular speed ω= v/R=qB/m
Bonus questions : what is the motion like if the velocity is not perpendicular to B ?
we break the velocity into components along the magnetic field and perpendicular to the
magnetic field. The perpendicular component will still produce circular motion. the parallel
Student : MengZi Guo
component produces no force and this motion is unaffected, thus the combination will be a
helical type motion.
Student : MengZi Guo
SPH4U Unit Test #2
Gravity, electric field and magnetic field .
* Note: There are more than 10 MC questions and more than 2 short answer questions in both
tests . Therefore, these tests can be rearranged into more copies to serve students better.
The MC questions on both test are put in the same order since there are 20 MC questions, so
teachers can take out their best 10 questions to make another copy of the test.
Multiple Choice Questions
[20 marks]
Select the best answer for each of the following questions :
1.Gravity is an _______force.
F. Attractive
G. Universal
H. Mutual
I. None of these
J. All of above
2.Weight is a measure of_________.
F. your mass.
G. the gravitational attraction between you and the earth.
H. mechanical equilibrium
I. all of these
J. none of these
3. In which case would you have the largest mass of an object? If the object weighed 1 N on the
Student : MengZi Guo
D. Jupiter
E. earth
F. moon
4.The gravitational force between 1kg of iron and earth is ___________ 1kg of marshmallows
and earth
E.
F.
G.
H.
greater than
less than
the same as
None of the above
5. What is static electricity?
D. electricity produced by friction
E. the energy of motion
F. the path along which electrons flows
6. crossing the wires in an electromagnet can reduce its magnetism
C. true
D. false
7. Electric current passing through a wire produces __________
E. a permanent magnet
F. a magnetic field around the wire
G. a compass
H. geographic poles
8. like charges repel, unlike charge attract and force between two charges is F=
is a description of _______.
E.
F.
G.
H.
Electrostatic forces acting between charges
Electromagnetism between charges
Potential Energy between charges
EM field
9. Magnetic field lines are same as lines of force
C. True
D. False
Student : MengZi Guo
10. Alternating current changes the ______of the current flow.
E. direction
F. amount
G. strength
H. voltage
11. Magnetic field lines that curve away from each other show
E. where the magnetic field is strongest
F. a magnetic domain
G. repulsion
H. attraction
12. Magnetic field lines _______
E. never cross.
F. cross at the north pole.
G. cross at the south pole.
H. cross halfway between the poles.
13. Magnetic fields are created by ___________
E. magnetic field lines
F. potential energy of molecules
G. spinning neutrons
H. moving electric charges
14. Different electromagnetic waves travel through vacuum at different speed
A. .True
B. False
15. _________is the measure of the force of gravity on an object.
E. mass
F. weight
G. density
H. equation
16. Electric Field lines always come from positive to negative charges
C. true
Student : MengZi Guo
D. false
17. which of the following in the universe is conserved.
G. energy
H. charge
I. linear momentum , p=mv
J. angular momentum
K. all of above
L. none of these
M.
18. If there is no test charge present to measure electric field, then electric field does not exist.
C. True
D. False
19. The ________around a positive charge points away from the charge, and decreases in
magnitude with distance r
E. Electricity
F. electric field
G. electric force
H. magnetic field
20. For each of the arrangements of velocity and magnetic field
below, determine the
direction of the force. Assume the moving particle has a positive charge.
A. into, down, right
B. down, into, left
C. out, down, right
D. into, up, left
Student : MengZi Guo
Short Answers.
1. a) Find the magnetic forces in following figures, JUSTIFY your answer : [ 3 marks each]
For the first figure, the F =0 since sin(0)=sin(180)=0, there is no force if v and B are either parallel or
antiparallel
For the second figure, the force is maximum when v and B are perpendicular to each other since
sin(90)=1.
b) Three points are arranged in a uniform magnetic field. The magnetic field points into the
screen.
i.
A positive charged particle is located at point A and is stationary. what is the direction of
magnetic force on the particle. Justify.
[ 3 marks]
ANS: The answer is zero since velocity is zero , therefore the force is also zero.
Student : MengZi Guo
ii.
The positive charge moves from point A toward C. what is the direction of magnetic
force on the particle? Justify.
[3 marks]
ANS: Up and left since the cross product is to the upper left and since the charge is positive the
force remains to be at upper left.
2. Four point charges, labeled 1 through 4, all with the same magnitude q are placed around the
origin as shown. the only negative charge is #2. what is the direction of the electric field at the
origin ?
[4 marks]
ans :
3. At what distance of location must we put two 1.00 micro Coulomb charges in order for the
repulsive force between them to be equivalent to the weight of a 1.00kg mass on earth ? [4 marks]
Q1 = 1.0 x 10-6 C and Q2 = 1.0 x 10-6 C
Felect = Fgrav = mg = 1.0 • 9.8 m/s/s = 9.8 N
d= 3.0cm
Student : MengZi Guo
4. The normal hydrogen atom consists of a proton nucleus and an orbital electron, each carrying
the fundamental charge of magnitude e= 1.60 x 10^-19 C. Assuming that the orbit is circular and
the separation between the particles is 5.3x 10^-11 meters. Find :
a) the force of electrical attraction between the particle [ 2 marks]
8.14 x 10^-8N
b) the gravitational force of attraction between them [ 2 marks]
3.61 X 10 ^-47N
c) which force is greater? how many times ?
[2 marks]
Electric force is greater, 2.25 x 10 ^-47 times greater.
communication problem
5.When a charged particle is fired into and perpendicular to a uniform magnetic field, it moves
along a circular path until it escapes the field. Is this statement true or false, justify your answer
in full details. Use a diagram to support your explanation. Find the expression of radius of the
orbit and angular speed . [ 6 marks]
Student : MengZi Guo
this statement is true. when a charged particle moves in a magnetic field it experiences a force
that is perpendicular to the velocity. since the force is perpendicular to the velocity, the charge d
particle experiences an acceleration that is perpendicular to the velocity. The magnitude of the
velocity does not change but the direction will change and produce a circular motion.
circular motion produces centripetal acceleration,
a= V^2/R, R is radius of orbit
Newton's second law gives us F=ma=m( v^2/R)=qvB
Thus, R=mv/qB
Angular speed ω= v/R=qB/m
Bonus questions : what is the motion like if the velocity is not perpendicular to B ? [3
marks]
we break the velocity into components along the magnetic field and perpendicular to the
magnetic field. The perpendicular component will still produce circular motion. the parallel
component produces no force and this motion is unaffected, thus the combination will be a
helical type motion.