14. Electromagnetism

Question 1

What is magnetic field?

Answer 1

Magnetic field is a region of space where a magnetic pole, a current-carrying conductor or a moving charged particle will experience a force.

Question 2

What direction does magnetic field lines run from?

Answer 2

Magnetic field lines run from the north-pole to the south- pole outside the magnet.

Question 3

What is magnetic flux density?

Answer 3

It is the force acting per unit length on a straight wire
which carries a unit current and is at right angles to the direction of the magnetic field.

Question 4

How to greatly increase the magnetic flux density ?

Answer 4

It can be greatly increased by the insertion of ferromagnetic material such as iron, cobalt, nickel into its core.

Question 5

What is ferromagnetic material?

Answer 5

Ferromagnetic material is categorised by its numerous small magnetic regions called domains. in unmagnetised state, all the elementary magnets are arranged randomly, displaying no magnetic properties.
When subjected to external magnetic field, elementary magnets line up in the direction of the external field and material is magnetised.

Question 6

What is the effect of ferrous core in solenoid?

Answer 6

It strengthens the magnetic flux density. This is due to the high degree of alignment of the magnetic domain in the ferromagnetic material. When the previously unaligned domains ‘line up’ it contribute to the field, hence causing an increase in magnetic flux density.

Question 7

What is the formula for force on a current carrying conductor?

Answer 7

F = B⟂ɪl
= B sin𝛉 ɪl
= Bɪl sin𝛉
F is the electromagnetic force (N)
B⟂ is the component of magnetic flux density (T) perpendicular to the current
ɪ is the current in conductor (A)
l is the length of conductor (m) WITHIN magnetic field
𝛉 is the angle between the conductor and the magnetic field

Question 8

What is the formula of a force on a moving charge?

Answer 8

F = Bqv sin𝛉

F is the force on the charge (N)
B is the component of magnetic flux density
q is the magnitude of the charge
v is the velocity of the charge
𝛉 is the angle between the conductor and the magnetic field

Question 9

What is the formula of the force on a charged particle moving in a circular motion in a magnetic field ?

Answer 9

F = B⟂ q v
= mv²/r
= mr𝜔²
F is the force on a charged particle moving in a circular motion
B⟂ is the component of magnetic flux density (T) perpendicular to the current
q is the amount of charged on the charge carrier
v is the velocity of the charge
m is the mass of the charged particle
r is the radius of the circular path
𝜔 is the angular velocity of the charged particle