1. DC MOTOR PRINCIPLE Magnetic Force

2. M OTOR P RINCIPLE  When a straight wire carrying a current is placed in 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.

3. M OTOR P RINCIPLE 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 in an external magnetic field, but is not parallel to the field, it experiences a magnetic force.

4. M AGNETIC F ORCE

5.  The magnetic force involved in the motor principle depends on three factors: 1. Amount of current through the wire  as the current increases, the magnetic force increases 2. Magnitude of the external magnetic field  as the strength of the external magnetic field increases, the magnetic force increases 3. 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

6. M AGNETIC F ORCE

7. An 8.50-cm length of conducting wire lies perpendicular to an external magnetic field of magnitude 4.20 mT [right] as shown in Figure 12.25.The SI prefix milli- (m) is equal to 103. If there is a current of 2.10 A in the conductor, calculate the magnitude and determine the direction of the magnetic force on the wire.

8. F ORCE BETWEEN TWO W IRES

10. M AGNETIC F ORCE Ampère placed two 1.50-m wires parallel to each other so that they were 4.80 cm apart. He delivered a current of 6.50 A to the wires. Both wires experienced an external magnetic field of 2.71x10 -5 T. Determine the force on one of the wires.