Magnetic Force and Motors

MAGNETIC FORCE AND MOTORSPhysics 12

Joke of the day:

Special song clip of the day:

Featuring Canadian ISS commander: Chris Hadfield!

http://www.wimp.com/singscollaboration/

Review:

page 767 # 1, 2

Remember RHR#1 Thumb of your right hand pointing in the

direction current and your fingers will wrap around the conductor in the direction of the induced magnetic field.

1 (a)

Current Coming Towards You

Current Moving Away From You

X

1 (b): note how the two magnetic fields combine to create one big loop on the outside

Both currents flowing towards viewer

1(c):

X

North

South

One current towards viewer and other current going away from viewer

RHR#2

Solenoids

Loops of Wire:

If the wire is shaped into a single loop, using RHR1, the behaviour of the magnetic field can be visualized

Solenoid:

If the wire is formed into many loops, a solenoid is created

And if we wrap a wire into several coils (and usually around a soft iron core) we create a solenoid that is also an electromagnet

Advantages of electromagnets: The strength of an electromagnet can easily be

changed by changing the amount of electric current that flows through it.

The poles of an electromagnet can even be reversed by reversing the flow of electricity.

Right Hand Rule #2:

Gives the direction of the North Pole in a solenoid Fingers curl in direction of current Thumb points to N pole

Force Experienced by Charged Particle in a Magnetic Field

Review: What is current?

I = q_ Δt It is a flow of electric charge. Is carried by moving electrons in a wire!

Hmmmm….moving electrons….so they have velocity!

What does this remind you of? Pipe cleaner time again! X represents magnetic

field into the board Let’s think about

directions: Velocity initially is….

To the right Field into the board What direction does the

force have to be acting in? Up or down

Oh no we’re in 3D now!

Charged Particle in Magnetic Field: The force acting on the charged particle is

proportional to speed and charge Magnitude and direction of force depend

on velocity of particle as well as magnitude and direction of magnetic field

When particle moves parallel to field, zero force experienced

Force acts perpendicularly to both velocity and field

RHR #3/ LHR#3:

Use to determine the direction of the force when the current and magnetic field are known

Thumb = force Index = magnetic field Middle = current

Right vs Left:

Use right hand if positive charge and left hand if negative charge

LeftRight

Video clip:

http://www.youtube.com/watch?v=HTTA30sEv6o

Practise:

Try it :

Practise sheet Work on lab