Download Unit B Review Package

3/21/2011
P30 Unit B: Electricity
and Magnetism Review
Package
Name: ________
Date: ________
Use the following information to answer the next question.
A student is investigating charging a neutral electroscope through induction and grounding.
The student brings a negatively charged rod near the neutral electroscope then touches the
electroscope to ground it. A student then brings a positively charged rod near the neutral
electroscope then touches the electroscope to ground it.
1. After grounding, the first electroscope will have a ___________ charge because electrons
have moved ___________ the grounded hand, the second electroscope will have a ___________
charge because electrons have moved ___________ the grounded hand. (positive, into,
negative, out of)
2. A point charge of magnitude 6.9 x 10-5 C produces an electric field of 1.0 x 103 N/C at point P.
a) Draw a diagram to represent this situation.
b) Determine the distance P is from the charge. (25 m)
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3. Determine the nature of the charge on X and Y. Justify your response. (-ive and –ive)
4. What is the distance between two protons when they exert force on each other of magnitude
4.0 x 10-11 N? (2.4 x 10-9 m)
5. Two small, oppositely charged spheres have a force of electric attraction between them of 1.6
x 10-2 N. What does this force become if each sphere is touched with its identical, neutral mate,
and then replaced twice as far apart as before? The mates are taken far away. (1.0 x 10-3 N)
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6. During a lightning strike, 30 C of charge may move through a potential difference of 1.0 x 108
V in 2.0 ms. Determine total energy released by this lightning bolt. (3.0 x 10 9 J)
7. What is the magnitude and direction of the electric field at point Z in the diagram below due to
the charged spheres at points X and Y? (2.0 x 105 N/C left)
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8. Determine the magnitude and direction of the electric field at point Z in the diagram below,
due to the charges at points X and Y. (1.2 x 105 N/C up)
9. Assume that a single, isolated electron is fixed at ground level. How far above it, vertically,
would another electron have to be, so that its mass would be supported by the force of
electrostatic repulsion between them? Record your answer to the nearest tenth of a meter. (5.1
m)
10. a) Two charged parallel plates are separated by a distance of 12 cm, as shown. The potential
difference between the plates is 750 V. A small positive test charge is placed between the plates
at three different positions, a, b and c. Determine the magnitude and direction of the electric field
experienced by the test charge in each position. (a, b and c are
equal)
b) In the parallel plate apparatus in the last problem, what would the electric field intensity
become if half of the charge were removed from each plate and the separation of the plates was
changed from 12 mm to 8.0 mm? (1.5 times larger)
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11. A ping-pong ball of mass 3.0 x 10-4 kg is hanging from a
light thread 1.0 m long, between two vertical parallel plates, as
shown. When the potential difference across the plates is 420 V,
the ball comes to equilibrium 1.0 cm to one side of its original
position.
a) What is the electric field intensity between the plates? (4.2 x
103 N/C)
b) What is the tension in the thread? (3.0 x 10-3 N)
c) What is the magnitude of the electric force deflecting the ball?
(2.9 x 10-5 N)
d) What is the charge on the ball? (7.0 x 10-9 C)
12. Which of the following is NOT a unit for the electric field?
a) V/m
b) N/C
c) J·m/C
d) C2/m2
13. A hollow conducting sphere is given a negative charge. When placing an electroscope near
the outside of the sphere, the leaves on the electroscope repel. When placing the same
electroscope near the inside of the sphere, the leaves do not repel.
a) Draw the electric field lines produced by this sphere.
b) Explain the results of the electroscope tests.
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14. The potential difference between two parallel plates is 8000 V. If a “free” electron is released
at the negative plate, with what speed does it hit the positive plate? (5.3 x 107 m/s)
15. A pith ball of mass 1.0 x 10-5 kg with a positive charge of 4.0 x 10-7 C is slowly pulled by a
string a distance of 50 cm through a potential difference of 8.0 x 102 V. It is then released from
rest and “falls” back to its original position. Calculate:
a) the work done by the string in moving the pith ball. (3.2 x 10-4 J)
b) the average force required to do this work. (6.4 x 10-4 N)
c) the kinetic energy with which the pith ball reaches its original position. (3.2 x 10- J)
d) its speed just as it reaches its original position (8.0 m/s)
16. A metallic ping-pong ball, of mass 0.10 g, has a charge of 5.0 x 10-6 C. What potential
difference across a set of horizontal parallel plates 25 cm apart would be needed to keep the ball
“floating” in the air? (49 V)
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17. a) Draw in the direction of the electric field in the diagram above. (left)
b) Determine the speed at which an electron will hit the screen. (3.0 x 107 m/s)
c) The diagram to the right shows the deflection coils and the
direction of the current passing through the coils. Label the
direction of the magnetic field on the diagram. (up)
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d) The diameter of the deflection coil is 7.5 cm. The coil has approximately 100 wraps of wire
and carries a current of 2.5 μA. Given that the electron follows a circular radius of 6.5 mm,
determine the magnitude of the magnetic field. (2.1 x 10-9 T)
18. In the diagram to the right, indicate
a) the direction of electron flow.
b) the north pole of the solenoid.
c) the magnetic field lines.
-ive
+ive
19. A 4.1 g wire is suspended in a magnetic field of 1.8 T. What must the current be if the wire
exposed to the magnetic field is 3.6 cm long? (0.62 A)
20. A bar magnet is moved left towards a loop of wire, as shown below. Draw
a) the poles on the bar magnet.
b) the direction of the induced magnetic field.
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