Download Electrcity UA

5/5/2017
P30 Unit B UA pt. A –
Electricity
Name: ______
Date: ______
Show all work, including starting equations, units and proper sig-digs, to receive full
marks.
1. In a classroom demo, the dome of a Van de Graaff generator was initially charged
negatively. A stream of closely spaced neutral soap bubbles was blown toward the dome
of the generator. Much to the surprise of the students, the following observations were
made:
1. The bubbles were initially attracted to the dome
until the first bubble hit the dome.
2. The first bubble hit the dome and splattered
3. All the other bubbles stopped in mid-air before
repelling from the dome of the generator and from
each other.
Using the concepts of electrostatic forces and charge distribution, explain:
 Why the soap bubbles were initially attracted to the top of the generator. (2
marks)
 Why, after the first bubble splattered, the other bubbles were repelled away from
one another. (2 marks)
A diagram or diagrams may be used to help you communicate your idea.
2. A single neutral 2.00 g pithball is touched by a charged
rubber rod which had a charge of 2.3 x 10-8 C. The pithball then
comes into contact with another pithball of equal size and
shape. If the two pithballs are hung by two pieces of 3.00 cm
thread from a single point (as shown) forming an angle of 15.0˚,
what is the charge remaining on the original charged rod?
(1.46 x 10-8 C) (4 marks)
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Use the diagram to the righ to answer the next
question:
3. A proton, electron and alpha particle are arranged as
shown above. Using your data table and the diagram
given, determine the magnitude and direction of the
electric force acting on the proton due to the alpha
particle and the electron.
(5.9 x 10-18 N 74° S of W) (6 marks)
4. Draw a diagram showing the field lines in each of the following situations. (You can
cut and paste the diagrams into your unit assignment!) (1 mark for each diagram)
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Use the diagram to the right to answer the next question.
5. In the early 1800’s Michael Faraday performed an
experiment used to investigate electric fields. This is
now called Faraday’s Ice Pail Experiment.
In the experiment, a hollow conducting ice pail is
placed on an insulated plate. One electroscope is
attached to the outside of the pail and one is attached to
the inside of the pail.
A positively charged rod is brought into the pail.
Predict which electroscope will show a deflection when the rod is brought into the pail
and justify your response using the principles learned in class (HINT: page 557-558 of
your Pearson) (3 marks)
6. A negative charged particle that has a mass of 2.8 x 10-16 kg accelerates upwards at 2.8
m/s2 in the electric field between two horizontal plates that have a separation of 0.15 m.
The potential difference across the plates is 4.2 x 102 V. Taking into consideration the
force of gravity, find
a) The magnitude and direction of the electric force on the particle.
(3.5 x 10-15 N up) (3 marks)
b) The magnitude of the particle’s charge.
(1.3 x 10-18 C) (3 marks)
7. An electron, travelling horizontally at a speed of 5.45 x 106 m/s, enters a parallel plate
capacitor with an electric field of 125 N/C between the plates. The separation between
the plates is 6.20 mm. Ignoring gravitational effects, if the electron passes from the top
plate to the bottom plate, how far will it have traveled into the capacitor? (0.130 m) (3
marks)
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8. Find the net electrical force exerted onto an object (q1 = +2.00 C) due to another
object (q2 = - 4.00 C) and an object on the opposite side (q3 = + 3.00 C) if q1 is
5.0cm away from each other charge.
9. Charge C (q = - 2.00 C) is 5.0 cm due west of charge B (q = + 8.00 C) and 6.0
cm due north of charge A (q = - 6.00 C). Determine the electrical force exerted
onto charge C. If charge C has a mass of 1.62 x 10-2 mg, at what rate will it
accerlerate?
10. An insulated hollow metal sphere with a diameter of 14.0 cm has a charge of 2.0
C added to it. Determine the electric field 6.0 cm from the surface of the sphere.
11. Determine the gravitational field strength and the electrical field strength 4.00 nm
from an electron.
12. What is the magnitude of the electric field when a charge of 4.00 x 10-12 C
experiences a force of 5.00 x 10-8 N after being placed inside this field?
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13. A + 8.00 C enters midway into the electric field (100 N/C) created by two
oppositely charged horizontal plates (positive on top) placed 24.0cm apart. If the
charge (m = 25.0 mg) enters with a horizontal velocity of 15.0 m/s right, find:
a) The vertical velocity of the charge 0.100 s after it enters the electric field.
b) The horizontal distance that the charge travels before it strikes the negative
plate.
14. An electron is placed (starting at rest) at the vertical negative plate across an
electric field from a vertical positive plate. When released, the electron moves
horizontally across the field and strikes the positive plate with a velocity of 4.00 x
106 m/s.
c) Determine the potential difference between the two plates.
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d) If the distance between the two plates is 3.00 cm, find the electric field
strength.
e) Determine the acceleration of the electron within the electric field.
15. A current of 3.60 mA flows through a circuit. How many electrons flow past a
given point in the circuit in 1.20 minutes?
16. A 60.0 W light bulb is 20.0 % efficient (20.0% of energy is actually converted to
light). The remaining energy goes into thermal energy. Determine the number of
joules the light bulb converts to light each minute and the number of joules of
thermal energy produced each minute.
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17. An electroscope is charged by induction by grounding briefly while using a
positively charged rod. Which of the following statements is true?
a) Some positive charge moves from the ground to the electroscope
b) Some positive charge moves from the electroscope to the ground
c) The electroscope becomes positively charged
d) The electroscope becomes negatively charged
18. If an electron is suspended midway between two horizontal electric plates that are
separated by a distance of 55 cm, what velocity will it hit the positive plate with
when the plates (E = 250 N/C) are turned on?
19. What potential difference exists when an alpha particle reaches a speed of 5.0 m/s
as it hits the negative plate in a uniform electric field?
20. What is the electrostatic force exerted on an electron through a 9.0 N/C field?
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21. What is the electrostatic force exerted on an electron when it experiences a
potential difference of 12.0 V at a distance of 6 cm from a charged plate?
22. What is the kinetic energy gained by an alpha particle accelerated from rest
through a potential difference of 3.00 x 105 V? What is this energy in electron
volts?
23. Two horizontal electrical plates are placed 25 cm apart, with the positive plate on
top. When turned on, the plates exert a potential difference of 15.0 V.
a) When an electron is positioned halfway between the plates and the plates are
turned on, what is the electrostatic force it experiences?
b) What is the net force it experiences?
c)
What is the acceleration it experiences?
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