Fields, Capacitance, Nuclear, Option

Question 1

Motor Effect

Answer 1

motor effect: when a current-carrying wire placed in a magnetic field experiences a force.

the force on a wire is:
- greatest when the wire is perpendicular to the magnetic field ( T = BIlndcos (0) )
- zero when the wire is parallel to the magnetic field ( T = BIlndcos (90) )

direction of force,current and field are related which we can find via fleming’s left-hand rule ( ie. if current is reversed or field is reversed then the direction of force is reversed)

Question 2

Electron beams undergoing a magnetic field

Answer 2

• beam is deflected downwards when a magnetic field is directed towards the vacuum tube
• each electron in the beam experiences a force due to the magnetic field
• the beam follows a circular path
• ## this is because the direction of the force on each electron is perpendicular to the direction of motionof the electron (and to the field direction)

Question 3

Why do current-carrying wires in a magnetic field experience a force?

Answer 3

The electronics moving along the wire are pushed to one side by the force of the field.

Question 4

How does the direction of motion of a charged particle in a magnetic field affect the force on the particle?

Answer 4

• force on a charged particle in a magnetic field = BQv

-The direction of motion of a charged particle in a magnetic field is at angle θ to the lines of the field
- the component of the field perpendicular to the direction of motion of the charged particle is given by Bsin θ

• if the velocity of the charged particle is perpendicular to the direction of the magnetic field, θ = 90°, so the equation is F=BQv
• if the velocity of a charged particle is parallel to the direction of the magnetic field, θ = 0, F= 0 so no force is experienced.

Question 5

Hall Probes

Answer 5

• hall probes are used to measure magnetic flux density
• they contain a slice of semiconducting material

how it works:
- a constant current passes through
- the charge carriers are deflected by the magnetic field
- a potential difference (hall voltage) is created between the top and bottom edges of the slice ( this is the hall effect )

• once the hall effect occurs charge carriers passing through the probe no longer are deflected because the forced caused by the magnetic field is opposed by the force of the electric field.
• the voltage produced is proportional to the magnetic flux density (provided a constant current)