Magnetic flux is the surface integral of the normal components of the magnetic field B over that surface. It is usually denoted as ∅. The SI unit of magnetic flux is Weber

∅ = BAcosø

∅ = Magnetic flux

B = Magnetic field

A = area

ø = Angle between a perpendicular vector to the magnetic field and magnetic flux

Magnetic flux density, B is the measure of the magnetic flux passing through a unit area in a plane at right angle to the flux. The SI unit of magnetic flux density is Weber per meter square (wb/m²), B = ∅/A

Magnemotive force (M.M.F) This is the flux which drives magnetic flux through a magnetic circuit (i.e the route or path which is followed by magnetic flux) and correspond to electromotive force (e.m.f) in an electric circuit. It’s usually measured in Ampere turns

F = IN, where F = Magnemotive force, I = current, N = number of turns

## state three factors in which the force on a current carrying conductor in a magnetic field depends

II. Strength of electric current

III. Length of the conductor

## Demonstrate the law of magnetic force of attraction and opposition with the aid of a diagram using a two bar magnets

- A conductor of active length 0.3m moves in a magnetic field at a linear velocity of 500m/s. If the magnetic flux density is 0.05T, calculate the average value of the induced e.m.f, if the direction of movement of the conductor is perpendicular to the field.

The average value of the induced e.m.f = magnetic flux density × length × velocity

Therefore e.m.f, E = BLV

B = 0.05T, L = 0.3m, velocity= 500m/s

0.3×0.05×500 = 7.5volts - A coil of 1000 turns and length 0.2m carries a current of 5A. If the cross sectional area of the magnetic circuit is proportional to the flux 1.0cm² and the flux produced by the coil is 0.15mWb. Calculate the permeability of the magnetic material.

L = 0.2m, N = 1000 turns, I = 5A, A = 1.0cm² = 0.01m², ∅ = 0.15mWb

Length= L, number of turns= N, current= I, area = A, flux = 0.15×10–³Wb

∅ = BA; B = ∅/A; B = 0.00015/0.01

Flux density, B = 0.015wb/m²

Magnetic field=H

H = IN/L

(5 × 1000) ÷ 0.2 = 25,000A/m

Calculate the permeability of the magnetic material

Permeability of the magnetic material = flux density/ magnetic field

B/H = 0.015/25000

6 × 10–⁷ Tesla/Ampere meter