Q1 A piece of wire passes through a uniform magnetic field of width 20 cm and flux density 2.5 T at an angle perpendicular to the direction of the magnetic field as illustrated in Fig 20.18. (i) What is the magnitude of the force when 2 A flows through the wire? (ii) In what direction does the force act?
Magnetic field into page
Current travelling from right to left
2.5 A
20 cm Fig 20.18
B = 6 T
5 cm Fig 20.19
Q3 A 3 C positively charged particle travels through a uniform magnetic field of flux density 5 T at a velocity of 4 103 m s1 at right angles to the field. Calculate the magnitude of the force on the particle.
Q2 A current of 2.5 A flows through a rectangular loop of wire, with dimensions 10 cm 5 cm.The loop is placed in a uniform magnetic field of flux density 6 T and is free to rotate about a central axis as shown in Fig 20.19. Calculate: (i) the magnitude of the force acting on each side of the loop (ii) the torque of the couple about the central axis. m
Q4 A proton enters a uniform magnetic field of flux density at a speed of 1.6 106 m s1.The force due to the field, of flux density 250 T, causes the proton to travel in a circular path of radius 6.68 105 m.The charge on a proton is 1.6 1019 C. (i) Calculate the magnitude of the force acting on the proton.
(ii) Use the radius of the circular path to calculate the mass of a proton.
Force
Force
Forces between currents Two current-carrying conductors will exert force on each other due to their magnetic fields.
The unit of electric current, the ampere, is based on this principle. Current-carrying conductors have magnetic fields around them.This is why they experience force when placed in magnetic fields.
Fig 20.20: The force on two current-carrying conductors on each other is due to the interaction of their magnetic fields
Definition of the Ampere AMPERE
The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible cross section and placed one metre apart in a vacuum,would produce a force on each conductor of 2 107 newtons per metre of length.
