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May 18th. 2004
Test #5 Electricity & Magnetism (SPH 4U1) Name:_________________
Part A: 20 Multiple Choice (Answer with the best choice):
1. The electrostatic force between two point charges is
charge on one of them triples, the force between them will be
a.
d.
N
b.
e.
N
c.
N
. If the distance between the charges is doubled and the
N
N
2. Which of the following is NOT a similarity or difference between Coulomb’s law and Newton’s law of universal
gravitation?
a. The forces act along the line joining the centres of the masses or charges.
b. The electric force can attract or repel, depending on the charges involved, whereas the
gravitational force can only attract.
c. The universal constant G is very small and in many cases the gravitational force can be
ignored. Coulomb’s constant k is very large, so that even small charges can result in
noticeable forces.
d. Coulomb’s law is the product of two masses, whereas Newton’s law of universal
gravitation is the product of two charges.
e. The size of the force is the same as the force that would be measured if all the mass or
charge is concentrated at a point at the centre of the sphere.
3. If point charge +q was absent, the magnitude of the electric field at point B would be E. What is the electric field
between the two point charges, +q and –q, at point B which lies at the midpoint between the two charges?
a. 2E [right]
d.
b. 0
e.
[left]
[right]
c. 2E [left]
4. The magnitude of the electric field between the plates of a parallel plate capacitor is 4.7  104 N/C. If the plates were
separated to a distance that is twice their original separation distance, the magnitude of the electric field would
a. double
d. decrease by a factor of sixteen
b. be halved
e. not be affected
c. decrease by a factor of four
May 18th. 2004
Test #5 Electricity & Magnetism (SPH 4U1) Name:_________________
5. If two parallel plates are 15 cm apart and have a field intensity of 1.2  102 N/C, the potential difference between the
plates would be
a. 18 V
d. 1800 V
b. 1.3  10–1 V
e. 7.2  1012 V
5
c. 2.2  10 V
6. How many electrons are present on a small sphere that has a charge of 7.4  10–4 C?
a. 2.1  10–16
d. 6.7  106 C
b. 1.2  1022 C
e. 4.6  1015
–22
c. 1.2  10 C
7. The potential difference between two parallel plates is 1.7  104 V. To move a small charge from one plate to another
opposing the electric field requires 0.56 J of work. The magnitude of the charge is
a. 3.0  104 C
d. 3.3  10–5 C
b. 9.5  103 C
e. 4.8  10–15 C
–15
c. 1.5  10 C
8. The direction of a magnetic field
plane of the page.
is from right to left as shown below. A proton travels into and perpendicular to the
The direction of the magnetic force acting on the proton is
a. down
b. up
c. right
d. left
e. directly out of the page and perpendicular to the paper
9.
FM
The direction of the positively charged particle’s velocity according to the diagram above must be
a. to the left
b. to the right
c. upward
d. out of the page, perpendicular to the page
e. into the page, perpendicular to the page
May 18th. 2004
Test #5 Electricity & Magnetism (SPH 4U1) Name:_________________
10. Magnetic field strength is measured in
a. N
b. N·C
c. kg/C·s
d. kg·m/s2
e. kg·m2/s2
11. A proton of charge 1.6  10–19 C is moving east with a speed of 8.2  107 m/s, as it enters a magnetic field of 2.5 T
directed downward. The magnitude and direction of the magnetic force acting on the proton is
a. 3.3  10–11 N [N]
d. 3.3  10–11 N [S]
11
b. 1.9  10 N [S]
e. 1.9  1011 N [N]
–12
c. 5.3  10 N [S]
12. A conductor is located between the poles of a horseshoe magnet. Current flows in the direction indicated by the
arrow on the diagram.
In which direction will the conductor move?
a. upward
b. left
c. downward
d. right
e. out of the page
13. Refer to the diagram below. As you start to pull the magnet upward through the horizontal loop of wire, in which
direction does the INDUCED current flow as viewed from above?
a. clockwise then counterclockwise
b. clockwise
c. counterclockwise then clockwise
d. counterclockwise
e. No current is induced.
14. A metal sphere has a charge of Q. It is touched to two neutral spheres that are identical to the first sphere and then the
three spheres are separated. The charge on each sphere is now
separated by a third neutral identical sphere. What is the charge on the third sphere?<br>
a) Q
b) 0.50Q
c) 0.33Q
d) 0.67Q
e) 0.25Q
May 18th. 2004
Test #5 Electricity & Magnetism (SPH 4U1) Name:_________________
15 Four charged spheres, A, D, P, and T are arranged as shown above. Sphere A has a charge of
has a charge of
C, sphere P has a charge of
C, and sphere T has a charge of
C. Which two spheres exert the smallest force on each other?
a. A and D
d. P and D
b. A and T
e. P and T
c. A and P
16. Two 2.0-kg spheres each carry a charge of 2.0 C. How does FE compare with Fg?
a. FE = Fg
b. Fg > FE
c. FE > Fg
d. If the charges on the spheres are the same, then Fg > FE, but if the charges are opposite
then FE > Fg.
e. FE and Fg cannot be compared without knowing the distance between the spheres..
17. Which of the following diagrams represents the field of force around a negative point charge?
a.
d.
b.
c.
e.
C, sphere D
May 18th. 2004
Test #5 Electricity & Magnetism (SPH 4U1) Name:_________________
18. The diagram below shows two point charges, B and C, and the electric field lines in the region around them.
Which one of the following statements is true?
a. A negative point charge placed at point A will move toward the left.
b. The charges on both B and C are negative.
c. The charges on both B and C are positive.
d. The electric field is strongest nearest point B.
e. A negative point charge placed at point A will move toward the right.
19. The charge, in coulombs, required to suspend a 1.7  10–13-kg oil drop in an electric field with intensity 2.5  105 N/C
is
a. 6.8  10–24 C
d. 6.7  10–18 C
–13
b. 4.3  10 C
e. 1.1  10–45 C
c. 6.1  10–14 C
20. A charge +q enters the area between two oppositely-charged plates through a hole in the positive plate. The charge
+q accelerates from rest and reaches the negative plate with a speed v. If a charge of +2q having four times the mass
entered the area through the hole and accelerated from rest, what would its speed be at the negative plate?
a. 2v
d. 0.707v
b.
e.
Part B: Full Solution
1. Two charges B = – 5.0 x 10-5 C and C = + 10.0 x 10-5 C are 1.0 m apart as shown in the diagram below.
a) Calculate the force between charge B and C.
b) Calculate the magnitude and direction of the electric field at point A due to the charged spheres at point B
and C.
0.5 m
mm
1.0 m
A
B
C
vb
2. Two horizontal platesgin a Millikan-like apparatus are placed 16.0mm apart. An oil drop of mass
3.00 x 10-15 kg remains at rest between the plates when a potential difference of 420.0 V is applied across the
plates, the upper plate being positive. Calculate the
a) Net charge on the oil drop
b) The sign of the charge on the oil drop
c) The number of excess or deficit electrons.
May 18th. 2004
Test #5 Electricity & Magnetism (SPH 4U1) Name:_________________
3. An electron is accelerated with an initial speed of 1.0 x 106 m/s through two parallel plates. The uniform electric
field between the plates has a magnitude of 3.0 x 102 N/C.
a) Calculate the work done on the electron by the field when the electron has travelled 2.0 cm
in the field.
b) Calculate the speed of the electron after it has travelled 2.0 cm in the field.
c) How far will the electron move into the field before coming to rest if the direction of the electric field is
reversed.
4. An electron (mass =9.1 x 10-31 kg) is moving in a circular path of radius 1.0 x 10 -4 m, in a plane perpendicular to a
uniform 0.1 T magnetic field. Calculate
a) The speed of the electron
b) What voltage is required to accelerate the electron, from rest in a vacuum, to this speed?
5. Compare the properties of gravitational, electric and magnetic fields.
May 18th. 2004
Test #5 Electricity & Magnetism (SPH 4U1) Name:_________________
ElectricityMagnetism
Answer Section
1C,2D,3C,4E,5A,6E,7D,8B,9E,10C,11A,12C,
13B,14A,15E,16C,17C, 18E, 19D,20D
Part B
Millikan a) -1.12 x 10-18 C b) negative c) 7.00