Electricity Unit Review ANSWER KEY
1. -Plutarch’s model: the rubbing of the amber heated the air and made the air
swirl around it and push the particles toward the amber.
- Gilbert believed that a fluid called effluvium came out of the charged
object and attached itself to the nearby objects and pulled them back
toward the charged object
- Dufay believed there were two types of fluid one for each type of charge.
The two fluids could balance each other. If there were more than one
type of fluid the object would be charged with that excess type of charge.
2. Benjamin Franklin was the first to use the terms positive and negative. He
proposed a one fluid model, where a lack of fluid produced a positive charge
and an excess of fluid produced a negative charge. He also said that current
flowed from positive to negative.
3. When J.J. Thomson discovered the electron, the static electricity model
shifted from a one fluid model to an electron particle model.
4. Conventional current is the apparent motion of positive charge from positive
to negative.
5. ‘Electron flow’, involves the motion of electrons from negative to positive.
6. There are two types of charge positive, caused by protons, and negative
charge caused by electrons. The protons are found in the nucleus of the
atom, while the electrons are found on the outside of the atom and can be
detached from the atom, creating the electron flow. Protons do NOT flow.
They stay in the nucleus.
7. ATTRACTION: Opposite charges attract, pull toward each other.
NOTE – It is possible for charged object to attract to neutral
objects (like tiny bits of paper) due to polarization [where the
electrons are moved to one side of the object].
REPULSION: Like charges repel, push away from each other.
8. For an object to be neutral it needs to have the same number of positive and
negative charges.
Atoms can be neutral,
and objects can be neutral.
9. Static electricity is the type of electricity responsible for the shock you get
from a doorknob after walking on a carpet.
10. When a rubber or ebony rod is rubbed with fur or wool, a negative charge
will be produced on the ebony rod. (A positive charge will be produced on
the fur or wool).
11. When a glass rod is rubbed with silk, or when an acetate sheet is rubbed with
a paper towel.
12. An insulator has material whose electrons can NOT detach and separate. The
electrons may shift sides, but will be unable to continuously ‘flow’ off of, or
through, the object.
A conductor has material whose electrons CAN detach and separate. The
electrons may leave the material and ‘flow’ off of the object. See diagram:
13. Static charge spreads evenly over the surface of the object because the
charges repel each other and spread out as far as possible from all other
similar charges. NOTE: If the object is not uniform in shape the charges will
NOT be evenly distributed. Charges tend to concentrate on points.
See diagram:
14. Polarization is caused by the movement of electrons within an object to the
same side. The object REMAINS NEUTRAL.
15. A neutral object can attract to a charged object due to polarization. The
unlike charged side of the polarized object, attracts to the fully charged
object.
16. An electrophorus is used to detect the presence of charge.
17. See the diagram BELOW:
18. When a object is charged by CONDUCTION the newly charged object will
have the SAME CHARGE.
When an object is charged by INDUCTION the newly charged object will have
THE OPPOSITE CHARGE.
19. See diagram:
20. If Charge B repels it would have to be negatively charged.
If charge B attracts it could be positively charged OR neutral (polarized).
21. If Charge B repels it would have to be positively charged. If charge B attracts
it could be negatively charged OR neutral (polarized).
22. The sphere B has to be neutral (polarized). If it was not neutralized it would
attract to one type of charge and be repelled by the other type of charge.
23. The majority of electricity in Manitoba is produced through
electromagnetism. The movement of coils of wire inside a magnetic field. In
Manitoba hydroelectric dams in the north of the province are used. The flow
of water is used to turn the coils of wire inside the magnets inducing electron
flow.
24. Electricity is like water being forced around and
around through a loop. The water pump is like
the battery or voltage, the work the water does
(say turning a propeller) is the resistance. The
rate of flow of water around the loop is like the
current.
25. In an open circuit the electrons can NOT flow
around and around. In a closed circuit the
electrons CAN flow around and around.
26. V stands for VOLTAGE and is measured in VOLTS (V)
I stands for CURRENT and is measured in AMPS (A)
R stands for RESISTANCE and is measured in OHMS (Ω)
27. Voltage can also be called “electric potential difference” or “electromagnetic
force (emf)”
28. V=E/q thus V=10J/2C V= 5v
29. q=E/V q=24J/3V
q=8C
30. The load in a circuit is what the electrons have to push through. The ‘load’ is
the resistance in the circuit. Resistors & load are synonyms.
31. The four factors that affect the resistance of a wire are:
a. The length of the wire…. The longer the more resistance
b. The diameter of the wire…the bigger the diameter the smaller the
resistance
c. The temperature of the wire…. The colder the wire the lower the
resistance
d. The type of material in the wire…
32. An ammeter measures the current.
33. R=V/I R=20V/5A
R=4 Ω
34. I=V/R
I=120v/10 Ω
I=12A
35. V=IR V=11A5.5 Ω
V= 2 v
36. Only (a)
37.
38.
39. Chemical, photoelectric, thermoelectric, electromagnetic piezoelectric
40. B) because it is located BEFORE the three bulbs in parallel and with it open
would not allow any current to flow in the ENTIRE circuit
41. t=Q/I t= 650C/12.5 A t= 52 s
42. Q=It Q=13.5A(55 s) Q=742.5 C
43. P=IV P=8A(120V) P= 960 W
44. I=P/V I=750W/120V I = 6.25 A
45. A circuit breaker prevents a circuit from overloading (causing wires to burn)
or a shortcircuit occurring. It will open the circuit at a certain current limit.
46. Parallel
47. Current cannot exceed 15 A: total power is 1950W and I=P/V I = 1950
W/120V I = 16.25 therefore the breaker WILL trip and open the circuit
48. 1. Switch off the lights when not in use 2. Use shorter showers. 3. Use energy
efficient lights.
49. Cost = kWh x time x rate Cost = 1500W/1000 x 365 x 2 x $0.07381 = $80.82
50. Cost of LED = 11W/1000 x 365 x 8 x $0.07381= $2.37
Cost of Inc. bulb = 100W/1000 x 365 x 8 x $0.07381 = $21.73
Cost savings = $21.73 - $2.37 = $19.36
51. Coal, Wind, Solar, Nuclear