11 magnetic Fields

What creates a magnetic field?

Moving charges and permanent magnets.

What is shown by the direction of a magnetic field line?

The direction of force on a free north pole.

Which direction do magnetic field lines flow in?

From north to south.

How is a uniform magnetic field represented by field lines?

Parallel

What does the spacing of magnetic field lines show?

Magnetic field strength/flux density.

How do you find the direction of the field lines around a current?

Using the right hand grip rule.

How is a field line or current running into the paper shown?

⊗

How is a field line or current running out of the paper shown?

. in a circle

Why does a current experience a force in a magnetic field?

The current's magnetic field interacts with the external one.

What is represented by the thumb in Fleming's Left Hand rule.

(Direction of) force

What is represented by the first finger in Fleming's Left Hand rule.

(Direction of the) magnetic field

What is represented by the second finger in Fleming's LHR?

(Direction of) current

When is Fleming's Left Hand Rule used?

To find the direction of a current/moving charge in a magnetic field.

When is the equation F = BIL sinθ used?

To find the magnitude of force on a wire (carrying current) in a magnetic field.

What is represented by θ in the equation F = BIL sinθ?

The angle between the current and the field direction.

What is the SI unit of flux density?

Tesla (T)

How is a magnetic flux density defined?

The field strength that would cause a wire carrying a current of 1A perpendicular to the field to experience a force of 1N per m of length.

What experiment can be done to find flux density in the lab?

Set up a current carrying wire between the poles of a magnet on top of a top-pan balance.

When is the equation F = Bqv used?

To find the force acting on a particle moving (at right angles) to a magnetic field?

When is the equation r = mv/BQ used?

To find the radius of the path of a particle moving in a uniform magnetic field.

Why does a charged particle describe circular motion in a uniform magnetic field?

(There is a constant) force always acting at right angles to motion.

Why do only particles with the correct velocity travel in a straight line in a velocity selector?

The electric force balance the magnetic force (at this velocity).