12.5 12.5 The Motor PrincipleThe Motor Principle

p. 563-566p. 563-566

Moving Conductors with Electricity:

Magnetic Force on a Magnetic Force on a Current-carrying ConductorCurrent-carrying Conductor

Michael Faraday experimented with the Michael Faraday experimented with the interaction between a magnetic field interaction between a magnetic field created by a current in a wire and the created by a current in a wire and the magnetic field of a permanent magnet. magnetic field of a permanent magnet.

He developed one of the first simple He developed one of the first simple electric motors.electric motors.

Although Faraday’s motor was not Although Faraday’s motor was not practical, it was later refined by other practical, it was later refined by other scientists to make it useful.scientists to make it useful.

Faraday’s MotorFaraday’s Motor

The copper wire moved because the The copper wire moved because the magnetic field in the copper wire magnetic field in the copper wire interacted with the magnetic field of the interacted with the magnetic field of the permanent bar magnetpermanent bar magnet

In figure 2a there are two separate magnetic fields; one is from current carrying conductor with conventional current going into the page. The other is from external magnets (from N to S). When two interacting fields are in the same direction there is a repulsion force

Since in same direction they will repel and conductor forced down

The Motor Principle A current carrying conductor that

cuts across external magnetic field lines experiences a force perpendicular to both the magnetic field and the direction of the electric current

Right-Hand Rule for the Motor Right-Hand Rule for the Motor PrinciplePrinciple

If the fingers of your open right hand If the fingers of your open right hand point in the direction of the external point in the direction of the external magnetic field and your thumb points in magnetic field and your thumb points in the direction of the conventional the direction of the conventional current, then your palm faces in the current, then your palm faces in the direction of the force on the conductordirection of the force on the conductor

Shorter way to remember “thumb direction of con. current,

fingers point south, palm faces force”

Analog Meters The 1st practical use of the motor principle; to

measure electrical quantities; the galvanometer-sensitive meter to measure current

On left side loop forced up and on right side forced down-causes needle to rotate toward right side of scale

Ammeters and VoltmetersAmmeters and Voltmeters Ammeter measures current; made Ammeter measures current; made

from galvanometer in parallel with a from galvanometer in parallel with a low resistance resistor. low resistance resistor.

Voltmeter measures voltage; made by Voltmeter measures voltage; made by placing galvanometer in series with placing galvanometer in series with high resistance resistorhigh resistance resistor

Factors Affecting the Factors Affecting the Magnetic ForceMagnetic Force

The magnetic force involved in the motor principle The magnetic force involved in the motor principle depends on three factors:depends on three factors:

the amount of current through the wire — as the the amount of current through the wire — as the current increases, the magnetic force increasescurrent increases, the magnetic force increases

the magnitude of the external magnetic field — as the magnitude of the external magnetic field — as the strength of the external magnetic field the strength of the external magnetic field increases, the magnetic force increasesincreases, the magnetic force increases

the length of the conducting wire that is the length of the conducting wire that is perpendicular to the magnetic field - as the perpendicular to the magnetic field - as the perpendicular component of the wire’s length perpendicular component of the wire’s length increases, the magnetic force increases.increases, the magnetic force increases.

Section 12.5

Right-Hand Rule for the Motor Principle

Match the terms next to the appropriate parts of the hand for this right-hand rule. Then, label the diagram below using the same terms to illustrate this rule. Draw in arrows indicating direction of force.

external magnetic

field

direction of current

force

palm: __________________

thumb: __________________

fingers: __________________

Section 12.5

Right-Hand Rule for the Motor Principle

Match the terms next to the appropriate parts of the hand for this right-hand rule. Then, label the diagram below using the same terms to illustrate this rule. Draw in arrows indicating direction of force. forcepalm: __________________

thumb: __________________

fingers: __________________

direction of currentexternal magnetic

field

external magnetic

field

force

direction of current

wire

external magnetic

field

direction of current

force

Homework Homework

P. 566 #1-3P. 566 #1-3 https://www.youtube.com/watch?v=

Ue6S8L4On-Y https://www.youtube.com/watch?v=f

WyzPdyCAzU