magnetism. chapter 19 problems 19-3 1,2,5,7 19-4 11,15,17 19-5 19,21,23 19-7 30-33, 19-8 36,38,39...

Magnetism

Magnetism

Chapter 19 Problems

19-3 1,2,5,7

19-4 11,15,17

19-5 19,21,23

19-7 30-33,

19-8 36,38,39

19-9 42,43

19-11 45,47

MagnetismOBJECTIVES After studying the material of this chapter, the student should be able to

1. Draw the magnetic field pattern produced by iron filings sprinkled on paper placed over different arrangements of bar magnets.

2. Determine the magnitude of the magnetic field produced by both a long, straight current carrying wire and a current loop. Use the right hand rule to determine the direction of the magnetic field produced by the current.

3. Explain what is meant by ferromagnetism, include in your explanation the concept of domains and the Curie temperature.

4. State the conventions adopted to represent the direction of a magnetic field, the current in a current carrying wire and the direction of motion of a charged particle moving through a magnetic field.

Objectives

5. Apply the right hand rule to determine the direction of the force on either a charged particle traveling through a magnetic field or a current carrying wire placed in a magnetic field.

6. Determine the magnitude and direction of the force on a current carrying wire placed in a magnetic field and a charged particle traveling through a magnetic field.

7. Determine the torque on a current loop arranged in a magnetic field and explain galvanometer movement.

8. Explain how a mass spectrograph can be used to determine the mass of an ion and how it can be used to separate isotopes of the same element

bar magnet galvanometer movement north pole magnetic moment south pole permeability of free space magnetic field ferromagnetism magnetic field strength right hand rule

mass spectrograph Curie temperature

KEY TERMS AND PHRASES

MAGNETS AND MAGNETIC FIELDS Two BAR MAGNETS exert a force on one another. If

two NORTH POLES (or SOUTH POLES) are brought near, a repulsive force is produced. If a north pole and a south pole are brought near then a force of attraction results. Thus, "Like poles repel, unlike poles attract”’

MAGNETS AND MAGNETIC FIELDS The concept of a field is applied to magnetism as

well as gravity and electricity. A MAGNETIC FIELD surrounds every magnet and is also produced by a charged particle in motion relative to some reference point. The presence of the magnetic field about a bar magnet can be seen by placing a piece of paper over the bar magnet and sprinkling the paper with iron filings.

The magnetic field produced by certain arrangements of bar magnets are represented in the diagrams shown below

MAGNETS AND MAGNETIC FIELDS The magnetic field lines drawn to represent the magnetic field produced by

certain arrangements of bar magnets are represented in the diagrams shown below

Notice the similarity between the lines of this slide and the previous slide particle distribution

FORCE ON A CHARGED PARTICLE MOVING IN A MAGNETIC FIELD

An electrically charged particle (q) moving through a magnetic field (B) at speed v may be acted upon by a force (F). The magnitude of the force F on the particle is

FORCE ON A CHARGED PARTICLE MOVING IN A MAGNETIC FIELD

An electrically charged particle (q) moving through a magnetic field (B) at speed v may be acted upon by a force (F). The magnitude of the force (F on the particle is

FORCE ON A CHARGED PARTICLE MOVING IN A MAGNETIC FIELD

is the angle between the direction of motion of the particle and the direction of the magnetic field. If = O, then the particle is traveling parallel to the field and no force exists on the particle (sin = 0). If = 90'. then sin 90'= 1, the particle is traveling perpendicular to the magnetic field and the force is a maximum.

FORCE ON A CHARGED PARTICLE MOVING IN A MAGNETIC FIELD

FORCE ON A CHARGED PARTICLE MOVING IN A MAGNETIC FIELD

ELECTRIC CURRENTS PRODUCE MAGNETISM A wire carrying a current (I) produces a

magnetic field. The magnitude of the magnetic field strength (B) a perpendicular distance r from a LONG, STRAIGHT WIRE the wire is given by

ELECTRIC CURRENTS PRODUCE MAGNETISM

The direction of the magnetic field produced by a current carrying wire can be predicted by using the RIGHT HAND RULE. The thumb of the right hand points in the direction of the conventional current in the wire. The fingers encircle the wire in the direction of the magnetic field.

ELECTRIC CURRENTS PRODUCE MAGNETISM

The magnitude of the strength of the magnetic field (B) at the center of a LOOP OF WIRE of radius r which carries a current I is

ELECTRIC CURRENTS PRODUCE MAGNETISM

The direction of the magnetic field at the center of the loop can again be predicted by using the right hand rule. The thumb is placed tangent to a point on the loop and is directed in the same direction as the current in the loop at that point. The fingers encircle the wire in the same direction as the magnetic field.

CONVENTIONS

Certain CONVENTIONS have been adopted in order to represent the direction of the magnetic field and the current in a wire. A magnetic field directed into the paper is represented by a group of x's, while a magnetic field out of the paper is represented by a group of dots.

CONVENTIONS

A current carrying wire which is arranged perpendicular to the page is represented by a circle. If the current is directed into the paper then an x is placed in the center of the circle. If the current is directed out of the paper then a dot is placed in the center of the circle.

FORCE ON A CURRENT CARRYING WIRE IN A MAGNETIC FIELD A current (I) in a wire

consists of moving electrical charges and a force (F) may be produced when a current carrying wire of length l is placed in a magnetic field. The magnitude of the force is given by the equation:

FORCE ON A CURRENT CARRYING WIRE IN A MAGNETIC FIELD

B is the MAGNETIC FIELD STRENGTH in tesla (T). Other units for magnetic field strength include newtons per ampere meter (N/A*m), newtons per coulomb meters per second (N/C*m/s), webers per square meter (wb/m2) and gauss (G).

FORCE ON A CURRENT CARRYING WIRE IN A MAGNETIC FIELD

is the angle between the directions of the current in the wire and the magnetic field. The force on the wire is zero if

FORCE ON A CURRENT CARRYING WIRE IN A MAGNETIC FIELD

A SECOND RIGHT HAND RULE is used to predict the direction of the force on the wire: "First you orient your right

hand so that the outstretched fingers point in the direction of the (conventional) current; from this position when you bend your fingers they should then point in the direction of the magnetic field lines, if they do not, rotate your hand and arm about the wrist until they do, remembering that your straightened fingers must point in the direction of the current. When your hand is oriented in this way, then the extended thumb points in the direction of the force on the wire."

FORCE ON A CURRENT CARRYING WIRE IN A MAGNETIC FIELD

FORCE ON A CURRENT CARRYING WIRE IN A MAGNETIC FIELD

FORCE ON A CURRENT CARRYING WIRE IN A MAGNETIC FIELD

Torque on a current loop

Torque on a current loop

Torque on a current loop

=r x F

F= I Bl, l = a, & r =b/2 so

ab =A (area of coil)

Torque on a current loop (Magnetic Moment)

If there are N loops then

IF we allow

then

Torque on a current loop (Magnetic Moment)

The Solenoid

Magnetic Field due to a straight wire

L

The direction of the magnetic field produced by a current carrying wire can be predicted by using the RIGHT HAND RULE.

Careful experiments show that the magnetic field is proportional to the current and inversely proportional to the distance from the wire

Magnetic Field due to a straight wire and the force between two parallel wires

L

Combining the two formulas yields

By using the right hand rule, the direction of the force is found to be towards I1 (attractive)

Magnetic Field due to a straight wire and the force between two parallel wires

L

The value of the constant

o= 4 x 10 -7 T*m/A is called the permeability of free space

The force per unit length acting on I2 is

is the equation

for the magnetic field caused by I1 acting on I2

Magnetic Field due to a straight wire and the force between two parallel wires