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## Physics II PHY 202/222 Magnetism

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### Physics II. PHY 202/222. Magnetism. 452 South Anderson Road. Rock Hill, SC 29730. www.yorktech.com ... MC: odd, SP: 1 19 odd. Beiser Chapters 29. SP: 3 ... – PowerPoint PPT presentation

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Title: Physics II PHY 202/222 Magnetism

1
Physics II PHY 202/222 Magnetism
• Rock Hill, SC 29730
• www.yorktech.com

2
Magnetism Test 5
Beiser Chapters 27 MC odd, SP 5 17
odd Beiser Chapters 28 MC odd, SP 1 19
odd Beiser Chapters 29 SP 3 Browne Chapter
26-29 for PHY 222 Students 26 1,5,9
27 2, 28 7 29 1, 2
3
Chapter 27 Magnetism
Beiser p.319
4
Magnets
When we think of magnets we either consider
permanent magnets or magnetic effects of moving
charge. Since permanent magnets come from moving
charge, we consider moving charge first.
Beiser p.319
5
Magnetic Fields
Unit of magnetic field is the Tesla where 1 T 1
N/Am 1 Weber/m2 10,000 Gauss The field
around a strong permanent magnet is 0.1 T. An
MRI is from 0.2 to 1.5 T. A junkyard
electromagnet for lifting cars is 1 T.
Beiser p.319
6
Magnetic Field of a Straight Current
Every current in a wire generates a magnetic
field. Point the thumb of your right hand in
the direction of the current, and your curled
fingers will point in the direction of the
field. The magnitude at a distance s from the
wire is given by the formula
Beiser p.320
7
Magnetic Field of a Loop
A current in a loop of wire generates a magnetic
field. Point the fingers of your right hand in
the direction of the current, and your thumb will
point in the direction of the field inside the
coil. The magnitude of the field inside the loop
is given by the formula
Beiser p.321
8
Earth Magnetism
The Earth has a magnetic field due to currents of
molten material in the core. The magnitude is
around 3 x 10 -5 T
Beiser p.322
9
Magnetic Force on a Moving Charge
A charge Q moving in a magnetic field B with
velocity v will experience force F. In the
picture, the charge is moving to the right in a
magnetic field into the screen. The magnitude of
the force is given by The force will be upwards
as follows Put the thumb of your right hand in
the direction of v. Put your fingers in the
direction of B. Curl fingers up. Force will be
in direction of fingers for a positve charge, and
opposite for a negative charge.
Beiser p.323
10
Magnetic Force on a Current
F I L B
The force will be upwards as follows Put the
thumb of your right hand in the direction of I.
Put your fingers in the direction of B. Curl
fingers up. Force will be in direction of
fingers.
Beiser p.323
11
Force Between two Currents
If currents are in opposite directions, the force
is repulsive same attractive.
Beiser p.324
12
Ferromagnetism
Beiser p.327
13
27.6
14
27.10
15
27.12
16
27.14
17
27.16
18
Chapter 28 Electromagnetic Induction
Beiser p.335
19
Electromagnetic Induction
• A current is produced if
• If a conductor is moved in a magnetic field
• If a magnet is moved near a wire, especially a
coil of wire
• A magnetic field changes near a conductor/coil.

For a straight conductor moving perpendicular to
a magnetic field.
Beiser p.335
20
For a magnet moving in a coil
Lenzs Law an induced current is always in the
direction so that its own magnetic field opposes
the effect that created it. Hence the negative
sign above.
Beiser p.335,6
21
Transformers
N1
N2
Beiser p.337
22
Self Induction
A change in current in a conductor causes a
change in magnetic field. A change in magnetic
field causes an self-induced emf.
Where L is the inductance of the circuit
component.
For a solenoid
Beiser p.339
23
Inductors in Combination
24
Energy of an Inductor
Beiser p.341
25
Time Constants and Current
When a switch in an inductive circuit is closed,
the current builds up to its full value
according to the formula
Where the time constant, T L / R.
Beiser p.341-3
26
28.4
27
28.6
28
28.8
29
28.10
30
28.12
31
28.14
32
28.16
33
28.18
34
28.20
35
Chapter 29 Alternating Current Circuits
Beiser p.350
36
Alternating Current
AC Alternating Current V Vmax sin ?t I Imax
sin ?t
DC Direct Current V constant
Beiser p.350
37
Generators
Split ring commutator
Slip rings
Generator Move the coil, electricity out.
Motor Electricity in, motion out.
38
Effective Values
Since the average AC voltage V Vmax sin ?t is
zero, we need a way to be able to calculate its
capacity to do work. So we use the effective
value or root-mean-square (rms) value.
Beiser p.350
39
Phase Angle
ELI ICE In an AC circuit with only an inductor
(L) the voltage (E) leads the (I) current by
900. In an AC circuit with only an capacitor (C)
the current (I) leads the voltage (E) by 900. In
AC circuits with both inductors and capacitors
you would have to find the phase angle as shown
in the book.
Beiser p.353
40
Maxwells Equations
Gausss Law for electricity Electric fields come
from charges
Gausss Law for Magnetism There are no magnetic
charges/monopoles. Any ball has the same B out
as in sum 0
Faradays Law Change in magnetic field makes
electricity.
Amperes Law Change in electric field makes
magnetism.
?E ? ?B ? ?E ? propagates through space as
light or other EM waves. WOW!
Browne p.343