Download How can you make the field stronger? Add more loops!!!

0Magnetic Fields and Magnetic force and Electromagnetic Induction
A. Magnetic Fields – permanent magnets
1. What are permanent magnets made of? Why can these materials
become magnets?
Iron, Nickel, Cobalt
2. Bar Magnet Magnetic field
Non-uniform, strongest at the poles
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3. Horseshoe magnet
Uniform field, strongest at
the poles
http://hendrix2.uoregon.edu/~dlivelyb/phys161/L8.html#emfields
B. Magnetic fields due to moving charge
1. Current-carrying wire
The ”first right-hand rule”
Higher current = Stronger
field
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How can the magnetic field strength be increased?
- Increase Current
- Add wires
- Loop the wire
2. Current-carrying loop
How can you make the field stronger? Add more loops!!!
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3. Bar electromagnet
2nd right- hand rule
A current can cause a piece of iron to become magnetized
C. Force on a moving charge (current) in a Magnetic Field
A magnetic field exerts a force on a moving charge, causing the
current stream to deflect or bend.
F = ILB
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The direction of the deflection is perpendicular to both the current
direction and the magnetic field line direction.
Examples:
http://www.cyberphysics.co.uk/Q&A/KS4/magnetism/motorEffect/questions_motor.html
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D. Earth’s Magnetic field
1. Sketch
http://www.bbc.co.uk/schools/gcsebitesize/science/21c/chemicals_in_our_lives/minerals_in_britainrev2.shtml
The geographic North is a Magnetic South
The geographic South is a Magnetic North
2. Consequences of the earth’s magnetic field:
Exerts a force on moving charges
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pg. 575 # 1,2,8-12
E. Electric Motor - converts electrical energy into mechanical work
http://www.cyberphysics.co.uk/Q&A/KS4/magnetism/motorEffect/questions_motor.html
F. Electromagnetic Induction- relative motion between magnet and
conductor (wire) produces a current!!
1. Faraday’s Law:
𝑉=𝑁
∆(𝐵𝐴)
𝑡
The induced voltage (and therefore the current) depends on
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G. Electric Generator
1. A generator turns mechanical work into electrical energy:
2. Examples of generators:
Coal plant:
http://www.stork-gears.com/images/coal_fired_powerplants.jpg
http://engineering.asu.edu/
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Nuclear power:
http://www.45nuclearplants.com/nuclear_reactor_designs.asp
Hydropower:
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H. Electric Power Transmission
1. Transformers
- Alternating current causes a changing magnetic field in a coil,
called the primary
- A current is then induced in the adjacent coil, called the
secondary. This current is AC, also. However, the Voltage may
be higher or lower depending on the ratio of turns in the primary
and secondary coils
2. Step-up transformer
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3. Step-down transformer
Activity: Make a transformer.
A. Objective:
B. Procedure/Materials:
1. Two electromagnets placed in close proximity
2. A switch to “mimic” a crude AC current
3. 3-V voltage source
4. Ammeter connected to secondary.
C. Data/ Discussion
1. Make a schematic illustrating your circuits. What is the appropriate
ratio of turns between your primary and secondary?
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2. Describe the readings on the ammeter when you simulated AC
current with the switch.
4. Power Lines
5. From power plant to home:
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Pg. 592 #2, 7, 10,13,14
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