Physics Chapter 25c

Magnetic Forces and Charges

Magnetic Forces and Charges

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

Magnetic Induction and Force Magnitude of the force is the field strength

multiplied by the amount of current and the length of wire

F = BILThis 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 Teslas1 T = 1 N/ 1 A.mB for Earth: 5 x 10-5 T

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 N I = 5.0 A L= 1.0 m

Equation:B = F/IL

Solve:B=(0.2N)/(5.0A)(1.0m)B= 0.04 T

Example A wire 1.0 x 101 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: