12.5 The Motor Principle p

Magnetic Force on a Current-carrying Conductor Moving Conductors with Electricity: Magnetic Force on a Current-carrying Conductor Michael Faraday experimented with the interaction between a magnetic field created by a current in a wire and the magnetic field of a permanent magnet. Michael Faraday experimented with the interaction between a magnetic field created by a current in a wire and the magnetic field of a permanent magnet. He developed one of the first simple electric motors. He developed one of the first simple electric motors. Although Faraday’s motor was not practical, it was later refined by other scientists to make it useful. Although Faraday’s motor was not practical, it was later refined by other scientists to make it useful.

Faraday’s Motor The copper wire moved because the magnetic field in the copper wire interacted with the magnetic field of the permanent bar magnet The copper wire moved because the magnetic field in the copper wire interacted with the magnetic field of the permanent 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

Magnetic Forces Between Two Current carrying Conductors Ampère’s law — ”conductors attract each other if the currents flow in the same direction and repel each other if the currents flow in opposite directions” Ampère’s law — ”conductors attract each other if the currents flow in the same direction and repel each other if the currents flow in opposite directions”

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

When a straight wire carrying a current is placed perpendicular to an external magnetic field, the interaction of the circular magnetic field produced by the current and the external magnetic field produces a magnetic force that acts on the wire. Note that the magnetic force is represented by the symbol  F m The action of the magnetic force on a conductor is known as the motor principle, which states that: “When a current-carrying conductor is placed perpendicular to an external magnetic field it experiences a magnetic force.”

Right-Hand Rule for the Motor Principle If the fingers of your open right hand point in the direction of the external magnetic field and your thumb points in the direction of the conventional current, then your palm faces in the direction of the force on the conductor If the fingers of your open right hand point in the direction of the external magnetic field and your thumb points in the direction of the conventional current, then your palm faces in the direction of the force on the conductor

Shorter way to remember “thumb direction of con. current, fingers point south, palm faces force”

Right-Hand Rule for Magnetic Force To determine the direction of the magnetic force in a straight conductor, use the right- hand rule: To determine the direction of the magnetic force in a straight conductor, use the right- hand rule: thumb indicates the direction of current (I) thumb indicates the direction of current (I) fingers point in the direction of the magnetic field (  B) fingers point in the direction of the magnetic field (  B) palm faces the direction of the magnetic force (  F m ) palm faces the direction of the magnetic force (  F m )

Analog Meters The 1 st 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 Voltmeters Ammeter measures current; made from galvanometer in parallel with a low resistance resistor. Ammeter measures current; made from galvanometer in parallel with a low resistance resistor. Voltmeter measures voltage; made by placing galvanometer in series with high resistance resistor Voltmeter measures voltage; made by placing galvanometer in series with high resistance resistor

Factors Affecting the Magnetic Force The magnetic force involved in the motor principle depends on three factors: The magnetic force involved in the motor principle depends on three factors: the amount of current through the wire — as the current increases, the magnetic force increases the amount of current through the wire — as the current increases, the magnetic force increases the magnitude of the external magnetic field — as the strength of the external magnetic field increases, the magnetic force increases the magnitude of the external magnetic field — as the strength of the external magnetic field increases, the magnetic force increases the length of the conducting wire that is perpendicular to the magnetic field - as the perpendicular component of the wire’s length increases, the magnetic force increases. the length of the conducting wire that is perpendicular to the magnetic field - as the perpendicular component of the wire’s length 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. force palm: __________________ thumb: __________________ fingers: __________________ direction of current external magnetic field force direction of current wire external magnetic field direction of current force

Homework P. 566 #1-3 P. 566 # L4On-Y 8L4On-Y 8L4On-Y 8L4On-Y PdyCAzU PdyCAzU PdyCAzU PdyCAzU