Magnetic Forces and Moving Charges

Flashcards based on lecture notes about forces on moving charges, motion in magnetic fields, velocity selection, and the Hall effect.

What equation is used to calculate the force on a charge moving in a magnetic field?

F = BQv sin θ, where B is magnetic flux density, Q is the charge, v is the speed, and θ is the angle between the magnetic field and velocity.

Explain the relationship between the force on a current-carrying wire (BIL) and the force on a moving charge (BQv).

The force on a current-carrying wire is the resultant of the forces acting on each of the moving charged particles (electrons) within the wire. The Qv term relates to the IL term as charge flow.

What is the 'Bev force,' and on what type of particle does it act?

The 'Bev force' refers to the force on a moving charged particle, particularly an electron (charge = e), in a magnetic field. F = Bev.

How do you determine the direction of the force on a moving charge in a magnetic field?

Use Fleming's Left Hand Rule.

Describe the motion of a charged particle moving in a uniform magnetic field perpendicular to its direction of motion.

The particle moves in a circular path with the magnetic force causing centripetal acceleration.

What is cyclotron motion?

The movement of charged particle at a constant speed in a circle

Define specific charge, and how can it be used to identify fundamental particles?

Specific charge (q/m) is the ratio of a particle's charge to its mass. If the speed and radius of the path are known, the specific charge can be found. If the charge is known, the mass may be determined. The technique can be used in nuclear research to identify fundamental particles.

Explain how electric and magnetic fields can be used in velocity selection.

By applying perpendicular electric and magnetic fields, particles with a specific velocity (v = E/B) will pass through undeflected, while others will be deflected.

In a velocity selector, what is the relationship between the electric force and magnetic force on an undeflected charged particle?

The electric and magnetic forces are equal in magnitude but opposite in direction, resulting in no net deflection.

What happens to a charged particle in a velocity selector if its velocity is higher than E/B?

The magnetic force will be stronger than the electric force, causing the particle to deflect in the direction of the magnetic force.

What is the Hall effect, and how is it used to measure magnetic flux density?

The Hall effect is the production of a potential difference (Hall voltage) across a conductor or semiconductor when a current flows through it in the presence of a magnetic field. A Hall probe, using this effect, can measure magnetic flux density.

What factors affect the Hall voltage (VH)?

The Hall voltage is affected by magnetic flux density (B), current (I), charge carrier density (n), thickness (t), and charge (q), as described by VH = BI / (ntq).