Transcript Electricity and Magnetism1

Electricity and Magnetism
Chapter 17 – Intro to Electricity
Chapter 18 – Electromagnetism
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1. Like charges _____ each other, unlike
charges ____ each other. (p. 423)

1. Like charges repel each other, unlike
charges attract each other. (p. 423)
2. What are the 3 ways that an object can
become charged? Explain each one.
 a. Friction: by rubbing 2 objects
together, electrons move from the
surface of 1 object to the other
resulting in an imbalance of charges.
 b. Conduction: electrons are
transferred from one object to another
by direct contact.
 c. Induction: Charges in an uncharged
object are rearranged without direct
contact.

3. What is static electricity? (p. 427)
 The buildup of electric charges on
an object.

4. How (and why) do lightning rods
protect buildings from lightning? (p. 429)
 Lightning rods direct the lightning
down
 into the earth where the charges
are dispersed without harm.

5. How is current electricity different
from an electric discharge?
 Electric current is the continuous
movement of electrons . Electric
discharge is the loss of static
electricity as charges move off an
object.

6. Order the following from the least
resistance to the most resistance: a thick,
short wire, a thick long wire, a thin long
wire, and a thin short wire. (p. 436)
 1.Thick short 2.Thin short OR 3.
Thick long 4.Thin long
 1.Thick short 2.Thick long OR 3.
Thin short 4.Thin long
 WHY?

7. Do the “Math Break on page 437 and
show your work.
 Use R = V / I and I = V / R
Remember, V = voltage in volts (V)
I = current in amperes (A)
 1. R = 10V x 0.5 A = 20 Ω
R = resistance in ohms (Ω)
 2. I = 36V/4 Ω = 9 A

8. What is a circuit, and explain the
difference between an open and closed
circuit? (p. 440 – 441)
 Circuit: a pathway for electrons to
travel;
 Closed Circuit: pathway is continuous
and the electrons will travel incessantly
through the circuit;
 Open Circuit: pathway is not
continuous and electrons will not
travel through this circuit


9. Draw a series and parallel circuit with a
power source, switch and 3 light bulbs.
Explain what happens when a light bulb
breaks in each circuit? (p. 442 – 443)
Series Circuit

Series:
When a bulb goes out in
a series circuit, the entire circuit
goes out. The burned out bulb acts
like an open switch.
Parallel Circuit

Parallel: In a parallel circuit, if a
bulb burns out, the other bulbs
continue to burn because each bulb
has its own independent circuit or
source of electrical current.
10. What does the switch do in the
previous drawings?
 The switch, if open, stops the
continuous flow of electrons. If
closed, it allows the continuous flow
of electrons.

11. How do circuit breakers and fuses protect
circuits?
 Fuses contain a thin strip of metal through
which charges flow. If the current is too
high, the metal in the fuse warms up and
melts, creating a break or gap in the
circuit.
 A circuit breaker is a switch that
automatically opens if the current in the
circuit is too high. Open circuit breakers
can be closed easily by flipping a switch
inside the breaker box once the problem
has been corrected.

12. How does a magnet impact a
compass? (p. 455)
 Causes the compass needle to point
North


13. Like poles of a magnet ____ each
other. Unlike poles of a magnet _____
each other? (p. 455)

Like poles of a magnet repel each other.
Unlike poles of a magnet attract each
other? (p. 455)
14. Explain what happens when you cut a
magnet in half (p. 458)
 You get 2 smaller magnets. Both
have a N and S pole.


15. An electric current induces a ______
field. (p. 462 – 463)

An electric current induces a magnetic
field. (p. 462 – 463)
16. How do you turn on and off an
electromagnet?
 By introducing an electric current
through a solenoid or removing the
electric current.

17. How do you make an electromagnet
more powerful? (p. 464)
 By adding more loops to the
solenoid.



18. Explain how an electric motor works? (p. 466)
An electric current in the armature causes
the magnet to exert a force on the
armature. Because of the direction of the
current on either side of the armature, the
magnet pulls up on one side and down on
the other, causing the armature to rotate.
As the armature rotates, the commutator
causes the electric current in the coil to
change directions. When the electric
current is reversed, the side of the coil that
was pulled up is pulled down, and the side
that was pulled down is pulled up. This
keeps the armature rotating.
19. What is electromagnetic induction and
how is it used to generate electricity? (p.
469 – 471)
 An electric current is produced by a
changing magnetic field. For
example, when a battery is
connected or disconnected, an
electric current is produced.



20. How are an electric motor and
generator similar?
They both have a rotating armature
between the poles of a magnet
creating an electric current. They are
basically the same machine acting in
reverse. An electric motor converts
electrical energy into kinetic energy
and a generator converts kinetic
energy into electrical energy.
21. Explain how you would use a transformer to
increase and decrease the voltage. (p 472)
 There are 2 types of transformers: Step-up
(used to increase the amount of voltage)
and Step-down (used to decrease the
amount of voltage). Step-up transformers
are used as electricity is leaving the power
station. This is to compensate for the loss
of electricity over a long journey to your
home. When the electricity arrives at your
home, it travels through a Step-down
transformer so that the electricity is at a
usable level inside your home.

22. When electricity enters your home
from the power lines it ________
 C. involves the flow of negatively
charged particles.

23. Static electricity is different from
current electricity because static
electricity occurs when _______
 C. negative charges move to an
object because of friction or
induction.

24. Lightning occurs when _____
 A. negative charges built up in the
clouds must be discharged to
positively charged areas or objects.


25. Which diagram shows the path of
electrical current in a circuit?
26. What do the three objects above
have in common?
 D. Electrical charges move easily
through these conductors.

27. If Bulb A burns out in the circuit
above, what would happen?
 B. Bulbs B and C would NOT light
because this is a series circuit.


28. Two magnets of equal strength are
placed end to end. How would you place
the two magnets so that they have the
strongest attractive force toward each
other?
29. A coiled wire is connected to the
positive and negative poles of a battery.
The current moving through the wire
produces an electric field. When you
move the compass to opposite ends of
the coiled wire, why does the compass
show an opposite direction for North?
 C. The electric field produced
around the coiled wire induced a
magnetic field.

30. Why is alternating current typically
used to deliver electricity to your school
or home?
 C. Power companies can easily
transmit high voltage AC current
and reduce it before it enters a
building.


31. Which diagram represents the best
transformer to deliver electricity from the
power lines to the house?

D A step-down transformer lower
high voltage current to a lower
voltage for use in your home.