Download Electricity

Name ________________________________
HOMEWORK Due Friday, Sep 11
Period: _______
Electricity
Define Key terms:
mechanical energy______________________________________________________________________
Convert______________________________________________________________________________
Filament_____________________________________________________________________________
I. Electric motors-definition
-Electric motors run off of electricity. The fan motor in the circuit kit was an electric motor. A drill is an
electric motor. A box fan is an electric motor.
- An electric motor changes electrical energy into mechanical energy (meaning electrical energy makes
stuff with an electric motor move)
II. Electric generators-definition
-Make electricity (they generate electricity) by using mechanical energy to spin a magnet near a copper
coil to create electricity.
-The mechanical energy used to spin an electric generator can be water through a dam (hydroelectric) or
wind (like windmills) or rising heat in a closed area with the turbine at the top (nuclear and coal power
plants).
Fill in the blanks with electric motor OR electric generator.
1. A fan is an _________________________.
2. Mechanical energy powers an ________________________.
3. This runs off of electricity. __________________________.
4. Spinning magnets near copper coils are parts of an _______________________.
5. Which statement describes the relationship between electric generators and electric motors?
A. Both electric generators and electric motors use motion in a magnetic field to produce electric current.
B. Both electric generators and electric motors transform current from a magnetic field into mechanical
energy.
C. Generators transform mechanical energy into electrical energy whereas electric motors transform
electric energy into mechanical energy.
III. Conductors and Insulators
-Metals are good conductors of electricity. They offer little resistance. Ex: copper(Cu), gold(Au),
silver(Ag)
-Insulators, like non-metals, are poor conductors of electricity. Wood, for instance, has 1 million times
the electrical resistance of copper. Ex: rubber, plastic, wood
6. Circle the three of the following that would make good conductors of electricity.
Aluminum
carbon
iron
plastic
wood
gold
7. Circle the two that would make good insulators.
Plastic
steel
wood
copper
silver
IV. Electrical resistance
8. Electricity is from moving electrons and therefore has a _____________ charge. As electricity passes
through a wire, it meets parts in the wire with a positive charge. Part of the electricity gets cancelled out.
9. The longer the wire, the more cancellations, and the (less, more) electricity that will pass through. For
this reason, you can’t run an extension cord from Horn Lake to Oxford even if you had enough cords
hooked together. The resistance would be too much.
Also for this reason, there need to be power stations located across the United States. If power
lines were hooked up from Hoover Dam in Nevada to the substation in Horn Lake, there would only be
about 1% of the original electricity because of the resistance.
10. Why can’t you run an extension cord from a home in Memphis to one in Hernando?
_____________________________________________________________________________
-Size of the wire-background information
Electricity is like water through a hose. A fire hose has less resistance to the water, and therefore
more water can move through the fire hose.
A garden hose cannot have as much water flow through because it has more resistance.
A thick wire has less resistance. More electricity can flow through a thick wire. This is why
electricity can flow through thick power lines the distance of Horn Lake to Oxford, but electricity cannot
flow through extension cord from Horn Lake to Oxford.
Thin wire has more resistance so less electricity flows through.
11. Which wire has more resistance to electricity?
A) thick wire
12. Which hose has more resistance to water? A) fire hose
B) thin wire
b) garden hose
V. The purpose of step-up transformers
Step-up transformers increase the amount of voltage to send electricity a long way (as far as 120
miles). Some electricity is lost due to resistance.
13. Why does electricity need to be stepped up between the power station and your house?
Some of the electricity is lost due to _________________.
VI. The purpose of step-down transformers
Step-down transformers decrease the amount of voltage coming into your house so it is safe to
use and doesn’t burn up your appliances.
14. Why does power need to be stepped-down before it gets to your house? (2 reasons)
________________________________________________________________________________
________________________________________________________________________________
15. What aspect of AC current makes it more suitable for long-distance transmission than DC current?
A. The current can be stored conveniently in batteries for later use.
B. The current can be easily transformed to higher or lower voltages.
C. The frequency can easily be altered.
16. Two lamps, one with a thick filament and one with a thin filament, are connected to a battery. What
explains why the lamp with the thicker filament burns more brightly?
A. Thin filaments offer less resistance and are better at conducting electrons through a circuit.
B. The lamp with the thin filament is closer to the battery, which causes the voltage to be higher.
C. Thick filaments offer less resistance and allow more current to flow through the circuit.
VII. Circuits
17. If a light bulb is “ON”, the circuit is:
A) open
B) closed
18. Which device is using resistors? A) A radio whose volume is on 10
19. Your house runs on a __________ circuit. A) parallel
20. When the lights are “OFF”, the circuit is _______.
B) A radio whose volume is on 4
B) series
A) open
B) closed
21. Which light bulbs would be brighter with the same amount of voltage flowing through the system?
A) three light bulbs in a series circuit B) three light bulbs in a parallel circuit
C) it doesn’t matter