MAGNETISM
1. INTRODUCTION
Magnetism is a fundamental force of nature arising from the motion of electric charges, manifesting as attractive interactions between objects. It governs phenomena from compass needles aligning with the earth magnetic field to advanced technologies like MRI machines and electronic motors.
Magnets exhibit distinct north and south poles, where like poles repel and unlike poles attract; breaking a magnet creates new pole pairs rather than isolated poles. Natural magnets like lodestone (Magnetite) were known since antiquity while electromagnets demonstrate magnetism from electric currents.
Magnetism or Electromagnetism in general, is the study of the production of a magnetic field when current is passed through a conductor.
1.1 Magnetic Fields and Lorentz Force
Magnetic fields
Magnetic fields are regions where magnetic forces can be felt, and they are generated by moving electric charges (currents) or by magnetic materials. A magnetic field is characterized by its direction and strength, represented by magnetic flux lines. It is a vector field describing the magnetic influence on moving charges, currents, and magnetic dipole.
Lorentz Force
Lorentz force is the force experienced by a charged particle when it moves through an electric field, magnetic field or both. It explains how charged particles behave in electromagnetic field. It is generally expressed as F = q(E+VxB).
Where F = Force acting on the particle (N)
Q = charge of the particle (c)
E = electric field strength (N/C)
V = Velocity of the charged particle (m/s)
B = Magnetic Flux density (T)
Components of Lorentz force
1. Electric Force: this force acts whether the particle is at rest or in motion and the direction is along the electric field for a positive charge and opposite for a negative charge.
2. Magnetic force: here the force acts only when the charged particle is moving and is the angle between the velocity and magnetic field. qvBsin . In addition, if the magnetic force acts on current carrying conductors placed in the magnetitic field B it is given by the expression F = ILBsin
Note: If V and B are in the same direction or parallel to each other, = 00 or 1800. Therefore, F = 0
If V and B are perpendicular or at right angles to each other, then = 9 00, therefore, F is maximum.
Example calculations
1. A particle of charge q and mass m moving with a velocity V enters a uniform magnetic field of strength B in the direction of the field. What is force of the field?
2. A charge of 1.6 x 10-19C enters a magnetic field of flux density 2.07 with a velocity of 2.5 x 107ms-1 at an angle of 30° with the field. Calculate the magnitude of the force exerted on the charge by the field.
3. The force on a charge moving with velocity V in a magnetic field B is half of the maximum force when the angle between V and B is?
4. Calculate the magnitude of the force due to a magnetic field of 0.40T on an electron moving perpendicular to the field with a speed of 4.00 x 6ms-1. [e = 1.60 x 10-19C]
5. A charge of 1.6 X 10-19C moving with a velocity of 2.5 x ms-1 enters a magnetic field of flux density 2.07 at an angle of 30° with the field. Calculate the magnitude of the force on the charge.
6. A conductor of length 2.5cm carries a current of 0.9A while kept a magnetic field of magnetic flux density 0.78T. Determine maximum force acting on it?