Download 1818 ACC Chemistry

Physics 4 – March 28, 2017

Do Now – Get together in groups to discuss your power station and
start on the powerpoint / paper for uploading.

Until 11:00 when we will transition to lesson for magnetism.
Objectives/Agenda/Assignment

Objective:


Ch 5.4 Magnetism
Assignment: p241 #37-46

Agenda:

Sources of magnetism

Magnetic field due to a wire

Magnetic flux density

Right hand rule for force

Magnetic force on current
carrying wire

Force between two current
carrying wires
Magnetism

Another fundamental property of matter.

Demonstrated by electrons and protons.

Has a polarity – a north and south pole, a direction

Exists as a field – a directional vector field

Sources include

Particles

Bar magnets

Current carrying wires and solenoids (coiled cylinder of wire)
Magnetic fields around sources
Direction of magnetic field

Fixed: From south to north

Current in wire: Right hand grip rule –
Thumb points in direction of current,
fingers curl around wire in direction
of circular magnetic field

Solenoid: Right hand grip rule –
Fingers curl in direction of wire
current around the solenoid, thumb
points in direction of the magnetic
field

Can be determined in lab using a
simple compass.
Magnetic Force

Magnetic fields produce a force on moving charges.

F = qvBsin

Magnetic flux density – measures the strength of a magnetic field.
Where q is the charge, v is the speed of the
charge, B is the magnetic flux density, and  is the angle between
the direction of the charge and the direction of the magnetic field.

Symbol: B

Unit: Tesla, T A 1 T magnetic flux density produces a 1 N force on a 1 C
charge moving at 1 m/s at right angles to the field.
Direction of the magnetic force

The Right Hand Rule: 3 equivalent versions:

Flat hand


Perpendicular 3 fingers


Thumb =charge velocity, Fingers = mag. field, Palm = force
Thumb = charge velocity, First = mag. Field, Middle = force
Finger curl motion

Fingers point = charge velocity, Palm/Curl fingers = mag.field, Thumb = force
Magnetic force on a current wire
F
= BILsin
Where B is the magnetic flux density, I is the
current, L is the length of wire in the field, and  is the angle
between the current and the magnetic field.

Direction of force given by the same right hand rule as for moving
charges, a current is a moving charge.

Force directions are defined for a positive moving charge or current

Recall that electrons move in the opposite direction to a current and
will experience the magnetic force in the opposite direction.
Force between parallel wires

Two wires can combine their magnetic fields in regular vector field
addition, just like we saw with electric fields.

Two wires can be parallel if the currents flow in the same direction
or anit-parallel if the currents flow in opposite directions.

Parallel currents create an attractive force

Antiparallel create a repulsive force
Definition of the Ampere

Remember we use the ampere as the fundamental SI base units for
all things electrical.

Why? Because it can be standardized through the magnetic force
between current carrying wires:

If the force on a 1 m length of two wires that are 1 m apart and
carrying equal currents is 2 x 10-7 N, then the current in each wire is
defined to be 1 Ampere.
Exit slip and homework

Exit Slip – A fixed bar magnet is aligned so that it’s north pole is due
north. What is the direction of the force of a charge that is traveling
due east past this magnet?

What’s due? (homework for a homework check next class)
 p241 #37-46
What’s next? (What to read to prepare for the next class)

 Read
11.1 Electromagnetic induction, p434 - 441