ELECTROMAGNETISM

LAB RESULTS

• CIRCUIT LAB – a compass needle deflected when placed near the circuit. WHY?

• ELECTROMAGNETIC INDUCTION LAB• Moving magnets result in current• The size of the induced current(as read on the galvanometer) was

bigger when we1. Used a stronger magnet.2. Moved the magnet at a faster speed.3. Used more turns of wire on the coil.

• WHY?

ANSWER TO CIRCUIT LAB

CURRENT INDUCES A MAGNETIC FIELD

• Current running through a conductor will produce a magnetic field

MAGNETIC FORCE

• A conductor that has current running through it, will also have a magnetic field surrounding it

• If this conductor is placed within the vicinity of ANOTHER magnetic field, the two fields influence on another via a magnetic force

MAGNETIC FIELD FOR LONG STRAIGHT WIRE

• B = Fmax / IL

• B = magnetic field in tesla

• F = maximum value of force on wire in newtons

• I = current in amperes

• L = length of wire in meters

Direction of Magnetic FieldYou can work out the direction of the field using your right

clenched fist.Point your thumb upwards in the same direction as the current.The direction of the field is the same direction in which your fingers curl.

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SAMPLE PROBLEM

• The force on a wire carrying 30.0A is a maximum of 3.80 N when placed between the pole faces of a magnet. If the pole faces are 25.0 cm in diameter, what is the strength of the magnetic field?

SOULTION

• B = Fmax / IL

• B = 3.80N/30.0A( .250meters)

• .507 Tesla

MAGNETIC FORCE

• B = Fmax / IL

• BIL = Fmax

• B( q/t) L = Fmax

• B(qL/t) = Fmax

• B(q)(L/t) = Fmax

• Bqv = Fmax

MAGNETIC FORCE

Fmag = qvBsin ө• Where q is the amount of charge

• v is the velocity of the particle

• B is the magnetic field

• ө the angle formed between the velocity and magnetic field directions.

• http://solar-center.stanford.edu/magnetism/magneticforce.html

http://www.waukesha.k12.wi.us/South/physics1/2.6/RHrule3.jpg

RIGHT HAND RULERight thumb points in the direction of the current. Your fingers, all point in the direction of the field. Your palm will then be in the direction of the magnetic force.

SAMPLE PROBLEM

• Determine the magnitude and direction of the force on a proton traveling in a vacuum tube at 2.84 x 105 m/s horizontally to the east in a vertically upward magnetic field of strength 1.60 T.

SOLUTION

Fmag = qvBsin ө• F = 1.6 x 10-19C(2.84 x 105 m/s )(1.60T)sin 90

• 7.27x 10-14 N• Direction – use right hand rule for force• Direction – out of paper or south

ANSWER TO ELECTROMAGNETIC

INDUCTION LAB

INDUCED CURRENT

• Just as a current flowing through a wire will produce a magnetic field,likewise a moving magnetic fieldnear a stationary wire will produce a current flowing through the wire.This is called induced current.

• gcsescience.com 

Induced Current in a Coil.When a magnet is moved towards and inside a coil of wire,

a current is induced inside the wire.

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INDUCED emf

• In order for an induced current to be generated- you must first have an induced electromotive force

A conductor near a moving magnetic field experiences separation of positive and negative charges within the conductor. This leads to an induced EMF across the conductor

http://bama.ua.edu/~calexand/PH102/labs/ind.htm

INDUCED EMF

• Ε = Blv• Ε= induced emf in volts

• B = magnetic field in tesla

• L = length of conductor in meters

• V= velocity of field relative to conductor

• (m/s)

PRACTICE PROBLEM

• A bar of length 10 cm slides along metal rails at a speed of 5 m/s in a magnetic field of 0.1 T. What is the motional emf induced in the bar and rails?

SOLUTION

• Emf= Blv

• Emf = .1T(.1m)(5m/s)

Emf = 5 x 10-2 V