Magnetic Fields Flashcards
What is a magnetic field?
A magnetic field is the force per unit current per unit length placed at a right angle to an external magnetic field.
What are the two main sources of a magnetic field?
Current-carrying conductors and permanent magnets.
How do magnetic field lines behave around a permanent magnet?
Magnetic field lines emerge from the north pole and enter the south pole.
What does the tangent to a magnetic field line represent?
It shows the direction of force on a ‘free’ magnetic north pole at that point.
Where is the magnetic field strongest?
Where the field lines are closest together.
How can the strength of a magnetic field in a solenoid be increased?
By increasing the current, increasing the number of turns per unit length, or using a soft-iron core.
What does the Right-Hand Grip Rule state for a straight conductor?
The thumb points in the direction of the current, and the curled fingers show the direction of magnetic field lines.
How do the field lines behave around a long, straight conductor?
They form concentric circles centered at the conductor, with spacing increasing as distance increases.
How does the magnetic field of a solenoid compare to that of a bar magnet?
The solenoid produces a similar field pattern to a bar magnet, with parallel field lines inside indicating a uniform field.
How do you determine the poles of a solenoid?
Use the Right-Hand Grip Rule, where the fingers show current direction and the thumb points to the north pole.
How does a ferrous core affect a solenoid’s magnetic field?
It increases the field strength by about 1000 times due to its higher permeability and its own magnetization.
What is Fleming’s Left-Hand Rule?
Thumb = Force, Index Finger = Magnetic Field, Middle Finger = Current.
How can the force on a current-carrying conductor in a magnetic field be increased?
By increasing the current or using a stronger magnet.
How do forces act between two parallel current-carrying wires?
If currents are in the same direction, the wires attract; if opposite, they repel.
What is the formula for magnetic flux?
Φ = BA (Magnetic flux = Magnetic flux density × Perpendicular area).
What is the formula for force on a conductor in a magnetic field?
F = BIL sin(θ).
When is the force on a current-carrying wire in a magnetic field zero?
When the wire is parallel to the field lines (θ = 0°).
What happens when the wire is perpendicular to the magnetic field?
The force is at its maximum (F = BIL).
How can a current balance be used to measure flux density?
By equating gravitational force (mg) to magnetic force (BIL).
What is the unit of magnetic flux density?
Tesla (T), where 1T = 1 N A⁻¹ m⁻¹.
What is the formula for force on a moving charge in a magnetic field?
F = BQv sin(θ).
What happens if a charged particle moves parallel to a magnetic field?
No force acts on it (F = 0).
How does a charged particle move if it enters a magnetic field at a right angle?
It follows a circular path due to the perpendicular force.
How does mass affect the radius of a charged particle’s circular motion in a magnetic field?
A heavier particle moves in a larger circle (r ∝ m).
How does velocity affect the radius of circular motion?
A faster-moving particle moves in a larger circle (r ∝ v).
How does the strength of the magnetic field affect the radius of circular motion?
A stronger field results in a smaller radius (r ∝ 1/B).
What is the Hall Effect?
The production of a voltage across a conductor when a magnetic field is applied perpendicular to the current.
Why is a semiconductor used in a Hall probe instead of a metal?
Electrons travel faster in semiconductors, making the effect more noticeable.
What happens to Hall voltage when the magnetic field direction is reversed?
The Hall voltage reverses.
What is the formula for Hall voltage?
VH = BI / (ntq).
What equation is used to find the specific charge (e/m) of an electron?
e/m = 2V / (r²B²).
What assumption is made in the charge-to-mass ratio experiment?
The electron’s kinetic energy equals the work done by the electric field.
What is a velocity selector?
A setup where electric and magnetic fields balance each other, allowing only particles with a specific velocity to pass through.
What is the equation for velocity in a velocity selector?
v = E/B.
