STARTERWhich way does the current point in this wire?

Magnetic Forces, Fields, and Directions

Directions Referenced to Your Sheet of Paper

The Force on a ChargeMoving Perpendicular to a

Magnetic Field

F = qvB q = charge in Coulombs

v = velocity in m/s

B = magnitude of the B- field

Direction of the Force on a Moving Charge in a B-Field

Point the fingers of your right hand in the direction of the velocity.Rotate your wrist until you can fold your fingers 90 degrees and point in the direction of B.Your thumb points in the direction of the force.

Example

A 2mC charge moving at 100m/s passes through a 2T B-field at right angles as shown. What force does it feel? What is the direction?

F =qvB = .002(100)2 = .400N , OUT

The Force on a Current-Carrying Wire Perpendicular to a Magnetic

Field

F = BiL

i = current in the wire in amps

L = length of the wire

B = magnitude of the B- field

Direction of the Force on a Current-Carrying Wire in a B-

Field

Point the fingers of your right hand in the direction of the current (i).Rotate your wrist until you can fold your fingers 90 degrees and point in the direction of B. Your thumb points in the direction of the force.

Example

A 2m long wire with a current of 10A is in a 2T B-field at right angles as shown. What force does it feel? What is the direction?

F = BiL = 2(10)2 = 40.0N , IN

B-Field of a Straight Wire

Direction of the Magnetic Field ( B) in a Current Loop

Rotate your fingers of the right hand around the loop in the direction of the current, and your thumb will point in the direction of the B – Field.

Direction of the Magnetic Field ( B) in a Current Loop

Rotate your fingers of the right hand around the loop in the direction of the current, and your thumb will point in the direction of the B – Field.

Magnetic Field Direction for Coils

Direction of the Force on a Moving Charge in a B-Field

Point the fingers of your right hand in the direction of the velocity.Rotate your wrist until you can fold your fingers 90 degrees and point in the direction of B.Your thumb points in the direction of the force.

Direction of the Force on a Current-Carrying Wire in a B-Field

Point the fingers of your right hand in the direction of the current (i).Rotate your wrist until you can fold your fingers 90 degrees and point in the direction of B.Your thumb points in the direction of the force.

Direction of the Force on a Current-Carrying Wire in a B-Field

Formula Summary Magnetic Fields and Forces

N = number of turns

I = current in amps

L = length of coil

𝐹=𝑞𝑣𝐵

Straight Wire Current Loop Coil (solenoid)

Force on a current in a B-FieldForce on a charged particle in a B-Field

m0 = 1.26 x 10-6 T.m / A

𝐵=𝜇𝑜 𝐼2𝜋𝑟

𝐵=𝜇𝑜 𝐼2𝑅 𝐵=

𝜇𝑜 𝐼𝑁𝐿

𝐹=𝐵𝑖𝐿

Practice – Find the direction of B at point P.

Direction is ________________?IN

Practice – Find the direction of B at point P.

Direction is ________________?OUT

Practice – Find the direction of B at point P.

Direction is ________________?

DOWN

Practice – Find the direction of B at point P.

Direction is ________________?UP

Practice – Find the direction of B at the center of the loop.

Direction is ________________?IN

Practice – Find the direction of the force on the wire.

Direction is ________________?LEFT

Practice – Find the direction of the force on the wire.

Direction is ________________?RIGHT

Practice – Find the direction of the force on the bottom wire.

Direction is ________________?UP

Practice – Find the direction of the force on the top wire.

Direction is ________________?Down

Practice – Find the direction of the force on the top wire.

Direction is ________________?Up