what we’ll need for today… magnets (bar and horseshoe) iron filings compasses two wires, 4...
TRANSCRIPT
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What we’ll need for today…
• Magnets (bar and horseshoe)
• Iron filings
• Compasses
• Two wires, 4 batteries in series, light bulb
• Electromagnets (solenoids)
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Electromagnetism
James Clerk Maxwell Michael Faraday
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Magnets: What do you know?
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Magnets – Key Points• Have poles (N and S) rather than + and – for charges• Like poles repel; Opposite poles attract• Produce a magnetic field: B
similar to gravitational field: g
and electric field: E• Magnetic Flux refers to the density of field lines
The Tabletop Explainer…
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Magnetic Field (B)
• Vector quantity (arrows)
• Points in direction a compass would point
• Runs from North to South
• Allows for FM: Magnetic Forces (the reason a compass needle moves!)
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Where does the electro come in?
• Current carrying wire….
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Current carrying wire…
• A static distribution of charges produces an electric field
• Charges in motion (an electrical current) produce a magnetic field
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1st RHR A moving electric charge produces a magnetic field
•Thumb: Direction of Current
•Fingers: Curl in direction of magnetic field
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What happens then…..
If we have a whole bunch of current carrying wire wrapped tightly?
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ElectromagnetsArranging wire in a coil and running a current through produces a magnetic field that looks a lot like a bar magnet
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Solenoid (electromagnet)
The 2nd RHR:
Fingers: Direction of current through solenoid
Thumb: Points to north pole
Cross section:
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Magnetic fields inside a solenoid
B = µo I n B: Magnetic Field Strenth (Tesla T)
µo : Permeability of free space =
4π x 10-7 T·m/A
I: Current (Amperes A)
n: Loops per meter = N/l
N: total loops l: length
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Example
A hollow solenoid is 25 cm long and has 1000 loops. If the solenoid has a diameter of 4.0 cm and a current of 9.0 A what is the magnetic field in the solenoid?
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3rd RHR
Applies to:
1.Charges moving in a magnetic field
2.A current carrying wire in a magnetic field
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Cross Product
Cross product: Vector product of two vectors. Gives a new vector that is orthogonal (perpendicular) to both
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3rd RHR
Direction:
Thumb: current/particle motion
Fingers: Magnetic Field direction
Force: Palm (positive); Knuckle (negative)
Mass spectrometer
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3rd RHRFor a charge moving in a magnetic field, a magnetic force is applied to it.
FM = q v x B (cross product)
For us…
FM = qvBsinθ q: charge
v: velocity
B: Magnetic Field strength
θ: orientation
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Example
A proton is fired into a magnetic field as follows:
Find/show:
a)It’s path
b)FM
c)Radius of it’s path
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3rd RHRFor a current carrying conductor, the magnetic force is as follows:
FM = B I l sin θ
If the conductor is perpendicular to the magnetic field:
FM = BIl B: Magnetic Field strength (T)
I: Current (A)
l: length of conductor (m)
θ: orientation
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3rd RHR
For a current carrying wire in a magnetic field, a magnetic force is applied to it.
FM = B I L sinθ B: Magnetic Field strength
I: current
L: Length of wire in magnetic field
θ: orientation