Magnetism Day 2 Charged Particles Moving Through Magnetic Fields.

Magnetism

Day 2Charged Particles Moving Through Magnetic Fields

When a charged particle travels through a magnetic field, it “might” experience a force.

When will it?

When won’t it?

When a component of the magnetic field is perpendicular to the particle’s velocity.

When the velocity of the particle and the velocity are either PARALLEL or ANTI-PARALLEL.

Right Hand Rule #1 (or RHR-1):

Finding the direction of the force exerted on a positive charge moving through a magnetic field         

Charged particle’s sign: +

Motion direction: East

Dir. of Magnetic Field: North

Dir. of Magnetic Force

Charged particle’s sign: -

Motion direction: East

Dir. of Magnetic Field:

Dir. of Magnetic Force South

Charged particle’s sign: -

Motion direction: North

Dir. of Magnetic Field: Downward

Dir. of Magnetic Force

Charged particle’s sign:

Motion direction: South

Dir. of Magnetic Field: West

Dir. of Magnetic Force Upward

Some Examples

More ExamplesCharged particle’s sign: -

Motion direction: West

Dir. of Magnetic Field: East

Dir. of Magnetic Force

Charged particle’s sign: +

Motion direction: Upward

Dir. of Magnetic Field: West

Dir. of Magnetic Force

Charged particle’s sign:

Motion direction: South

Dir. of Magnetic Field: Upward

Dir. of Magnetic Force West

Charged particle’s sign: +

Motion direction:

Dir. of Magnetic Field: South

Dir. of Magnetic Force East

OK, so RHR-1 gives us the direction of the force. But since force is a

vector, can we find the MAGNITUDE of the force?

qvBFmagnetic

Magnetic Field Strength (measured in Teslas, T)

Velocity of the particle (m/s)

Charge of the particle (C)

NOTE: This equation is only valid if B and v are perpendicular to each other!!!

What exactly is a Tesla?

• 1 T = _____________

• 1T is REALLY big. So we often us prefixes like mT, T, or nT.

• The earth’s magnetic field is soooooo small that we often use a term called a GAUSS (G) to measure it.

• 1 G = 0.1mT (and the earth’s magnetic field is ~ .1-.3 G)

€

1N /(C⋅ ms )

But what if v and B are NOT perpendicular?

sinqvBFmagnetic

Magnetic Field Strength (measured in Teslas, T)

Velocity of the particle (m/s)

Charge of the particle (C)

The angle between v

and B

sinqvBFmagnetic

What if = 0? F = ____

What if = 90? F = ____

What if = 180? F = ____0

0

qvB

What would happen if ……

What would you have to do to make the path helical?

+ -

qB

mvr

r

mvqvBFF

r

mvFqvBF

cmag

cmagnetic

2

2

Mass Spectrometer

Only ions with a certain speed make it through….thus, if an ion makes it through, it must have the same speed as all the other ions that make it through.

Use the radius of the motion to find the mass.

qB

mvr