Devil physics The baddest class on campus IB Physics...
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DEVIL PHYSICS THE BADDEST CLASS ON CAMPUS IB PHYSICS
Transcript of Devil physics The baddest class on campus IB Physics...
DEVIL PHYSICS THE BADDEST CLASS ON CAMPUS
IB PHYSICS
TSOKOS LESSON 5-6 MAGNETIC FIELDS
IB Assessment Statements
Topic 6-3, Magnetic Force and Field
6.3.1. State that moving charges give rise to magnetic fields.
6.3.2. Draw magnetic field patterns due to currents.
6.3.3. Determine the direction of the force on a current-carrying conductor in a magnetic field.
IB Assessment Statements
Topic 6-3, Magnetic Force and Field
6.3.4. Determine the direction of the force on a charge moving in an electric field.
6.3.5. Define the magnetic field and direction of a magnetic field.
6.3.6. Solve problems involving magnetic forces, fields, and currents.
Objectives
Understand the meaning of magnetic field and find its magnitude and direction in simple situations involving straightline conductors
and solenoids
using the right-hand rule
where appropriate
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Objectives
Find the force on moving charges
and currents,
in magnetic fields and appreciate the definition of the ampere as a fundamental SI unit, using the right-hand rule for forces where appropriate.
sinqvBF
sinBILF
Electric Field, Magnetic Field
A charge will generate an electric field around itself
Any other charge (small positive test charge) that enters the field will experience a force on it = electric force
Electric Field, Magnetic Field
Same is true for a magnet or an electric current (moving charge)
Each of these produce a magnetic field around them
When another magnet or electric current enters the magnetic field, it will experience a force on it
Direction of magnetic field is determined by relation to magnetic field of the earth
Electric Field, Magnetic Field
Electric Field, Magnetic Field
Magnetic Fields
Magnetic fields are produced by permanent
magnets and by electric currents
Magnetic Field from Coil
Magnetic Field from Solenoid
Magnetic Field from a Loop of Wire
Magnetic Field from a Loop of Wire
Magnetic Field from a Straight Wire
Electric Field, Magnetic Field
Magnets and electric currents (moving charges) produce magnetic fields around them
When another magnet or electric current enters the magnetic field, it will experience a force on it
Force on a Current
Force on a Current
Force on a Current
Using the right hand place the thumb in the direction of the current and the fingers in the direction of the magnetic field. The direction away from the palm is the direction of the resulting force.
Force on a Current
Current
Field
Force
Thumb
Fingers
Palm
Force on a Length of Wire
Θ is the angle between the current and the direction of the magnetic field
sinBILF
Force on a Length of Wire
Θ is the angle between the current and the direction of the magnetic field
sinBILF
I
B
θ
Magnetic Force on a Moving Charge
sinBILF
t
qI
tvL
sin
sin
qvBF
tvt
qBF
Magnetic Force on a Moving Charge
sinqvBF
Magnetic Force on a Moving Charge
Work Done by Magnetic Force
None
Since the magnetic force is always perpendicular to the velocity, it cannot do work
Magnets in particle accelerators merely deflect or direct particles
Electric fields are used to increase the particle’s kinetic energy
Orsted’s Discovery
The magnitude of the magnetic field B created by the current in a wire varies linearly with the current in the wire and inversely with the perpendicular distance from the wire.
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What does that remind you of?
What does that remind you of?
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Orsted’s Discovery
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Orsted’s Discovery
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µ0 is the magnetic permeability of a vacuum
(ε0 is the electric permittivity of a vacuum)
27
0 104 ANx
Orsted’s Discovery
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Unit for the magnetic field is the tesla (T)
Magnetic field of the earth at the surface is 10-4 T
A high voltage transmission line carrying a 2000 A current produces a magnetic field of 8x10-5 T
Direction of the Magnetic Field
Direction of the Magnetic Field
Strength of the Magnetic Field
Field Strength from Single Wire Loop
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Field Strength from a Solenoid
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Field Strength Between Two Current-Carrying Wires
Field Strength Between Two Current-Carrying Wires
Field Strength Between Two Current-Carrying Wires
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0sinBILF
LIr
IF
LIBF
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LIr
IF
LIBF
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Field Strength Between Two Current-Carrying Wires
The force on each wire will be the same, even though the magnetic fields produced by each wire individually is different
r
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LIr
IF
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120
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r
qqkF 21
r
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Fun Facts:
The Ampere is defined through the magnetic force between two parallel wires. If the force on a 1m length of two wires that are 1m apart and carrying equal currents is 2x10-7 N, then the current in each wire is defined to be 1 A.
Fun Facts:
The coulomb is defined in terms of the ampere as the amount of charge that flows past a certain point in a wire when a current of 1 A flows for 1 second.
Summary: Are you able to
Understand the meaning of magnetic field and find its magnitude and direction in simple situations involving straightline conductors
and solenoids
using the right-hand rule
where appropriate
r
IB
2
0
L
NIB 0
Summary: Are you able to
Find the force on moving charges
and currents,
in magnetic fields and appreciate the definition of the ampere as a fundamental SI unit, using the right-hand rule for forces where appropriate.
sinqvBF
sinBILF
QUESTIONS?
Homework
SL: #1-20, 23, 25-27, 30-32
HL: #1-32, skip 21, 22, 24, 28, 29
