Download Chapter 19-3 and 20

19-3 Magnetic Force
► Charged
particles at rest are not affected by magnetic field
(stationary)
► When moving, charged particles can be deflected by
magnetic fields
► Used in TV tubes to create picture on screen
► Earth’s magnetic field deflects charged particles from outer
space (cosmic rays)
Magnetic Force on a charged particle
𝐹𝑚𝑎𝑔 = 𝑞𝑣𝐵
q = charge
v = velocity
B = magnetic field
FB is a centripetal force
● A charge moving
through a magnetic
field follows a
circular path
Magnetic Forces and Current-Carrying Wires
► Current-carrying
wire placed in magnetic field is deflected
► Reversing current cause deflection in opposite direction
► Greatest deflection occurs when current is perpendicular to
magnetic field
Force on a wire
𝐹𝑚𝑎𝑔𝑛𝑒𝑡𝑖𝑐 = 𝐼𝐿𝐵
► Two
parallel
conducting wires exert
a force on one another
► When two conductors
are parallel, the force
on a wre is based on
magnetic field created
by the other wire
► When current is in the
same direction, force is
attractive
Meters
► Meters
use magnetic needle
 Current moving through wires in meter creates magnetic field that
interacts with magnetic field of needle
 Cause needle to be deflected (like repel, etc.)
 Amount of deflection indicates amount of current
Loudspeakers
Galvanometer
use of magnetic force on
a wire to produce sound
waves
device that operates on a
torque acting on a
current loop in a
magnetic field that causes
a coil to twist
20-1 Electricity from Magnetism
► The
process of creating a current in a circuit loop by
changing the magnetic flux in the loop is called
electromagnetic induction.
Electromagnetic Induction
► Imagine a wire moving to the
right as shown.
 According to the RHR the
magnetic force is directed
upward
 This force will separate the
charges.
 As negative charges move
upward, the wire will develop
a potential difference.
Electromagnetic Induction
► Three
ways to induce a
current in the coil
► Vary the size of the coil (ex:
as coil enters the field the
area increases)
► Change the orientation of the
coil
► Change the strength of the
magnetic field
Chapter 20
Characteristics of Induced Current
► Lenz’s
Law
The magnetic field of the induced current is in a direction to
produce a field that opposes the change causing it.
► This rule can be used to find the direction of the current in the
loop.
► Note: the induced current does not oppose the applied field, but
rather the change in the applied field.
► The magnitude of the induced emf can be predicted by Faraday’s
law of magnetic induction.
Faraday’s Law
► The
magnitude of the induced emf depends on
the number of loops (N), the magnetic flux (M),
and the rate of change.
► M = AB cos
Classroom Practice Problem
►A
coil with 25 turns of wire is moving in a uniform magnetic
field of 1.5 T. The magnetic field is perpendicular to the
plane of the coil. The cross-sectional area of the coil is 0.80
m2. The coil exits the field in 1.0 s.
 Find the induced emf.
 Determine the induced current in the coil if the coil’s resistance is
1.5 .
► Answers:
 3.0  101 V, 2.0  101 A