Download elec and mag study guide KEY - SmithScience

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Physical Science - Study Guide - Electricity and Magnetism
1. The diagram shows two copper spheres. Sphere 1 is negatively charged, and Sphere 2 is neutral.
a. How will charge be transferred when the two spheres touch?
Charge will be transferred by conduction when one charged object touches another.
b. What charge will Sphere 2 have?
Sphere 2 will pick up a negative charge.
c. After they touch, will the charge of Sphere 1 be more, less, or the same than in
the diagram?
The charge of Sphere 1 will be less negative.
2. If a neutral metal comb is held near an object with a negative charge, the comb will become charged by _induction__
3. When charge is transferred, the subatomic particle involved is the _electron__________________
4. If the two charges represented in the figure below were brought near each other, they would __attract_________
5. In walking across a carpet, how is charge being transferred?
Electrons are being transferred by friction.
6. Which materials allow charges to flow easily? Give examples!
Conductors like metals
Which materials make it difficult for charges to flow? Give examples!
Insulators like woo and plastic
7. Give 4 ways to reduce the resistance of a metal wire.
a. shorten the wire
c. increase the wire thickness
b.lower the temperature
d. choose a different type of wire
8. A complete path through which charge can flow is an electric __circuit__________________.
9. Give the unit and unit symbol for the following quantities.
a. Electrical Power: __watts (W)___________, ___P____
c. Current: __amperes_(A)___________, __I_____
b. Potential Difference:_volts_(V)__________, __V____
d. Resistance: __ohms_(Ω)___________, __R____
Calculations
Show all of your work to solve the following calculations problems. Include correct units.
10. What is the current through a generator that generates 5000 Watts of power and has a potential difference of 250 V?
Given: P = 5000W
P = IV
V = 250V
I = P/V
I=?
I = 5000W/250V
I = 20A
11. If the voltage in a circuit is 80 volts and the resistance is 20 ohms, what is the current?
Given: V = 80V
V = IR
R = 20 Ω
I = V/R
I=?
I = 80V/20Ω
I = 4A
12.
What is the power used when 120 Volts pushes a current of 10 Amps?
Given: V = 120V
P = IV
I = 10A
P = 10A x 120V
P=?
P = 1200W
13. What is the voltage in a circuit if the current is 4 amps and the resistance is 4 ohms?
Given: I = 4A
V = IR
R = 4Ω
V = 4A x 4Ω
V=?
V = 16V
14. The current in a clothes iron measures 5.0 amps. The resistance of the iron is 24 ohms. What is the voltage?
Given: I = 5A
V = IR
R = 24Ω
V = 5A x 24Ω
V=?
V = 120V
15. A series circuit has a current of 5 A. The circuit contains a 10- resistor. What is the voltage of the circuit?
Given: I = 5A
V = IR
R = 10Ω
V = 5A x 10Ω
V=?
V = 50V
16. A flashlight bulb connected to a 8-V battery draws a 0.5-A current. What is the power used by the flashlight bulb?
Given: V = 8V
P = IV
I = 0.5A
P = 0.5A x 8V
P=?
P = 4W
Use the circuit drawings to answer questions 17-19.
17. Label the circuits in the above diagram as series or parallel. A:_series__________ B:___parallel_________
18. Which circuit, if any, would have the brighter bulbs? How do you know?
The parallel circuit would have the brighter bulbs since each bulb is receiving the full current.
19. Based on the circuit diagrams, what would happen to the other bulbs if one of the bulbs in Circuit A burned out?
If one of the bulbs in circuit A burned out, all of the other bulbs would go out too.
What would happen to the other bulbs if one of the bulbs in Circuit B burned out?
If one of the bulbs in circuit B burned out, the other bulbs would still light.
20. Are most of the circuits in your home series or parallel? How do you know?
Most of the circuits in the typical home are in parallel so that everything doesn’t shut down if one lightbulb goes out.
21. Calculate the current for each circuit. Show your work!
I = P/V
I = 9W/15V = 0.6A
I = P/V
I = 16W/9V = 1.8A
I = P/V
I = 15W/12V = 1.25A
I = P/V
I = 18W/12V = 1.5A
22. The diagram below represents a closed circuit. How much current flows through the circuit? Show your work!
Given: V = 12V
R = 6Ω
I=?
V = IR
I = V/R
I = 12V/6Ω
I = 2A
23. Draw a series Circuit and a Parallel circuit, each with a 9-V battery, and 3 resistors. How many pathways does the
current have to flow in each circuit?
9V
9V
1 pathway
3 pathways
24. Like poles __repel____ and opposite poles __attract____________ each other.
25. How does the magnetic force exerted by a magnet change as the distance between two magnets increases?
The further apart the two magnets get, the weaker the attractive force.
26. The region where a magnet’s force is strongest is at the ___poles______________________.
27. Draw 3 magnets arranged end-to-end so that there will be no attraction between them.
N
S
S
S
N
N
S
28. What will happen to the poles of a permanent magnet if you cut the magnet in half? How many total poles will there
be between the two magnets? You may draw a picture.
There will be 4 total poles. Each magnet will have a N and a S pole.
29. Define “magnetic domain.”
Magnetic domain is the tiny groups of atoms whose electrons are all aligned in the same direction.
30. Explain the difference in the magnetic domains of temporary and permanent magnets.
In permanent magnets, the domains are always aligned. In temporary magnets, the domains are induced to align when
an electric charge is applied and they revert as soon as the charge stops.
31. How can a permanent magnet be demagnetized?
You can heat it to a specific point, you can rub it with a stringer magnet in the direction opposite of its poles, you can hit
or drop it repeatedly.
32. How can we artificially create magnetism?
We can induce magnetism by running a current through a wire wrapped around an iron core.
33. Moving a magnet inside a coil of wire will induce a voltage in the coil. How can the voltage in the coil be increased?
Increase the size of the coil of wire.
34. A coil of wire that is carrying a current and produces a magnetic field is a ___solenoid_________________________
35. A student builds an electromagnet using a variable power source and 40 turns of wire. The electromagnet is used to
pick up metal paper clips. The student changes the voltage and counts the number of paper clips that are picked up.
What will happen to the number of paper clips the magnet picks up as the voltage increases?
The number of paper clips will increase.
36. What 3 properties can you change to increase or decrease the strength of an electromagnet?
1. the number of turns of wire
2. the amount of current running through the wire
3. the amount of iron in the core