Download Magnetism-Magnetic Induction

Magnetism-Magnetic Induction
By David Kimball, Emma Kaplan, Nate
Rudolph
Big Idea
• Magnetism can produce electric current, and
an electric current can produce magnetism.
Electromagnetic induction
• In 1831, two scientists Michael Faraday, and
Joseph Henry individually discovered that
magnetism could produce an electrical current
• Electric current can be produced in a wire by
moving the magnet through the coiled wire.
Electromagnetic Induction cont.
• No power source is required to produce the
current
• The production of voltage depends only on
the relative motion of the conductor with
respect to the magnetic field
• The amount of voltage depends on how fast
the magnetic field lines are traversed by the
wire
Induction
• The number of coils also increases the
induced voltage and current in the wire.
– Twice as many coils will induce twice as much
voltage
Faraday’s Law
• The induced voltage in a coil is proportional to
the product of the number of loops, the cross
sectional area of each loop, and the rate at
which the magnetic field changes within these
loops.
• This law describes the relationship between
induced voltage and the rate of change of a
magnetic field
Generators/Alternating Current
• A motor converts electrical energy into
mechanical energy
• A generator converts mechanical energy into
electrical energy
• When the magnet is pushed into and out of
the coiled wire the voltage switches between
a positive and negative value
Simple generators
• Starting perpendicular to the field, the loop
crosses the maximum amount of magnetic
field lines.
• As it rotates it switches between the magnetic
field lines, voltage is produced
• Generators change mechanical energy to
electrical energy
• (picture on the next slide)
Transformers
• A transformer works by inducing a changing
magnetic field in one coil, which induces an
alternating current in a nearby second coil
• It changes the voltage of the energy
• Only AC current can be transformed
• The voltage is either stepped up or stepped
down depending on the ratio of coils of the
primary to the secondary
Transformers (Cont.)
• If the secondary has a hundred times as many
turns as the primary, then a hundred times as
much voltage will be induced
• With a transformer, energy is conserved. The
power used in the secondary is supplied by
the primary.
• If the voltage is increased, the current is
decreased
Multiple Choice Questions
• 1. According to Faraday’s Law, how can an
electric current be produced?
a. spinning a magnet
b. wrapping a wire
c. rubbing a magnet on another object
d. moving a magnet through coiled wire
• 2. Increasing the number of loops of wire that
move in a magnetic field ________ the
induced voltage and the current in the wire.
a. decreases
b. increases
c. does not affect
d. eliminate
• 3. The force that you exert on the magnet
_________ the distance that you move the
magnet is your input work.
a. multiplied by
b. divided by
c. subtracted from
d. added to
• 4. A generator converts ______ energy to
_______ energy.
a. mechanical, electrical
b. electrical, mechanical
c. thermal, mechanical
d. electrical, radiant
• 5. A motor converts ______ energy to
_______ energy.
a. mechanical, electrical
b. electrical, mechanical
c. thermal, mechanical
d. electrical, radiant
• 6. What does a transformer change?
a. current
b. resistance
c. voltage
d. power
• 7. In a transformer, if the secondary has half
as many turns as the primary, then _______ as
much voltage is induced in the secondary.
a. one fourth
b. four times
c. twice
d. half
• 8. If 120V is used to power a toy electric train
that operates at 6V then a ______ transformer
should be used that has a primary to
secondary turns ratio of ________.
a. step up, 20/1
b. step up, 1/20
c. step down, 20/1
d. step down, 1/20
• 9. What is the main benefit of AC compared to
DC?
a. it has the ability to transform
b. it is alphabetically superior
c. DC is more widely used
d. it alternates
• 10. If the first set in a transformer produces
10V with a current of 6 amps and the second
half a transformer has 5 amps, what is the
voltage in the second half of the transformer?
a. 1V
b. 5V
c. 10V
d. 12V
Answers
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1. D
2. B
3. A
4. A
5. B
6. C
7. D
8. C
9. A
10. D