Magnetic Force/Field

Magnetic Field

• North/South Pole• Opposites attract• Unit: Tesla (T)

• Field lines point in direction that a North Pole would feel a force

Earth behaves magnetically as if a bar magnet was located near its center

Magnetic Force on a moving Charge

• 1. Charge must be moving• 2. Velocity must have a component perpendicular to the

direction of the magnetic field

Direction of Force is perpendicular to both velocity and field

RHR #1Fingers = B FieldThumb = velocity or currentPalm = Force

Why? (such a weird direction)

What happens near the poles where the charges are not deflected?

Force on a moving ChargeF = B * qo(v sin θ) (N)

• What is the force on a 2μC charge moving at 4.3x104 m/s perpendicular to a 0.4 T magnetic field?

A proton (m= 1.67x10-27 kg, q= 1.6x10-19 C) is moving with a velocity, v= 6.3x10-5 m/s, and enters a region with a magnetic

field of 0.4 T. What is the radius of the circle that the charge will move through? What is the final velocity of the charge?

Force on a current in a wire:F = I l B sin(θ)

• A square loop (10cm) of wire has a current of 5A flowing clockwise and is placed in a 0.4T magnetic field directed into the page. What is the magnitude and direction of the force on each segment of the loop?

X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X

Torque on a loop:N I A B sin(φ)

• A square loop (10cm) of wire has a current of 2A flowing clockwise and is placed in a 0.75T magnetic field directed to the right. What is the magnitude and direction of the torque on the loop?

A square loop (10cm) of wire has a current of 2A flowing clockwise and is placed in a 0.75T magnetic field as shown below. What is the

magnitude and direction of the torque on the loop?

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