Magnetic Field: - A Magnetic Field Is A Region in Which A Body With Magnetic Properties Experiences A Force
Magnetic Field: - A Magnetic Field Is A Region in Which A Body With Magnetic Properties Experiences A Force
Magnetic Field: - A Magnetic Field Is A Region in Which A Body With Magnetic Properties Experiences A Force
I
Fleming’s Left Hand Rule
F I B
F Isin
Magnetic Flux Density
• The magnetic flux density is defined as
the force per unit length per unit current
acting on a current-carrying conductor at
right angle to the field lines.
F
B
I
o 4 107 T m A -1 (H m -1 )
B o nI
1
B' o n
2 Distance from the
centre of the sole
12 0 1
2 noid
Magnetic Flux Density due to Some
Current-carrying conductors(1)
o NI
• Circular coil B
2r
8 o NI o NI
• Helmholtz coils B 0.72
125r r
Magnetic Flux density due to Some
Current-carrying Conductors (2)
Force on a moving charge in a
magnetic field
• The force on a moving charge is proportional
to the component of the magnetic field
perpendicular to the direction of the velocity of
the charge and is in a direction perpendicular
to both the velocity and the field.
F qvB sin
Fmax qvB for v B
F 0 for v // B
http://webphysics.davidson.edu/physlet_resources/bu_semester2/c12_force.html
Right Hand Rule
F q v B
Free Charging Moving in a
Uniform Magnetic Field
• If the motion is • In general, with the
exactly at right motion inclined to
angles to a uniform the field, the path is
field, the path is
helix round the lines
turned into a circle.
of force.
Mass Spectrometer
• The mass spectrometer is used
to measure the masses of atoms.
qE qvB
• Ions follow a circular
path in this region.
mv 2
qvB'
r
Aurora Borealis (Northern Lights)
• Charged ions
approach the Earth
from the Sun (the
“solar wind” and are
drawn toward the
poles, sometimes
causing a
phenomenon called
the aurora borealis.
Causes of Aurora Borealis
• The charged particles from
the sun approaching the
Earth are captured by the
magnetic field of the Earth.
• Such particles follow the
field lines toward the poles.
• The high concentration of
charged particles ionizes
the air and recombining of
electrons with atoms emits
light.
http://www.exploratorium.edu/learning_studio/auroras/selfguide1.html
Hall Effect
• When a current carrying conductor is held firmly
in a magnetic field, the field exerts a sideways
force on the charges moving in the conductor.
• A buildup of charge at the sides of the conductor
produces a measurable voltage between the two
sides of the conductor.
• The presence of this
measurable transverse
voltage is called the
Hall effect.
Hall Voltage
• The transverse voltage builds up until the
electric field it produces exerts an electric
force on the moving charges that equal and
opposite to the magnetic force.
• The transverse voltage produced is called the
Hall voltage.
Charge Carriers in the Hall Effect
o I1 I 2
F
2a
• Note that the force exerted on I2 by I1 is equal
but opposite to the force exerted on I1 by I2.
Definition of the ampere
• The ampere is the constant current which, if
maintained in two parallel conductors of infi
nite length, of negligible cross-section, and
placed one metre apart in a vacuum, would
produce between these conductors force of
2 x 10-7 N per metre of length.
Torque on a Rectangular Current-
carrying Coil in a Uniform Magnetic Field
• Let the normal to the coil plane make an
angle with the magnetic field.
• The torque is given by NBAI sin
Moving Coil Galvanometer