1. Physics Chapter 25c

2. Magnetic Forces and Charges

4. Force created by moving charge Remember the third left hand rule: Not only can we determine direction, but we can determine magnitude of the force created by moving current Magnitude depends on 3 things: Strength of the (external) magnetic field (B) Amount of current in the wire Length of the wire present in the magnetic field

5. Magnetic Induction and Force Magnitude of the force is the field strength multiplied by the amount of current and the length of wire F = BIL This assumes wire is perpendicular to magnetic field! Rearrange this equation to have an equation for the strength of the magnetic field (magnetic induction): B = F/IL B measured in Teslas 1 T = 1 N/ 1 A. m B for Earth: 5 x 10 -5 T

6. Example A 1.0 m wire carries a current of 5.0 A. The wire is at right angles to a uniform magnetic field. The force on the wire is 0.2 N. What is the magnitude of the magnetic induction? Known: F = 0.2 NI = 5.0 AL= 1.0 m Equation: B = F/IL Solve: B=(0.2N)/(5.0A)(1.0m) B= 0.04 T

7. Example A wire 1.0 x 10 1 cm long is at right angles to a uniform magnetic field with induction 0.060 T. The current through the wire is 4.0 A. Find the force on the wire. Known: L = 0.10 m B = 0.060 T I = 4.0 A Equation: F = BIL Solve: