b) A square coil is placed in a
uniform magnetic field of flux density 40 mT. The plane of the coil is normal
to the magnetic field. The coil has 200 turns and the length of each side of
the coil is 3.0 cm.
magnetic flux Φ
the coil 
magnetic flux linkage for the coil. 
plane of the coil is turned through 90°. What is the change in the magnetic
flux linkage for the coil?
shows a step-down transformer. The primary coil has 1150 turns and the
secondary coil has 30 turns. The ends of the secondary coil are connected to a lamp
labelled ‘6.0 V, 24 W’. The ends AB of the primary coil are connected to
an alternating voltage supply. The potential difference across the lamp is 6.0
the current in the lamp. 
b. Calculate the input voltage to the primary
c. Calculate the current in the primary coil,
assuming the transformer is 100% efficient. 
student suggests that to avoid the production of heat in the transformer the
wires should be coated in a material that is a poor conductor of heat. Explain
why this is not a sensible suggestion. 
b) When the switch is closed, the
electromagnet is magnetized and attracts one end of the iron armature. The contacts
closes (2nd switch) and allows current to flow in the second circuit. When the
1st switch is open again, the current to the electromagnet is cut, the
electromagnet demagnetizes and the 2nd switch is opened. Current stops flowing
in the second circuit.
c) in industries( controlling large power
loads),electric fuel pump, motor control
Increasing the speed of rotation
Increasing the number of turns
Using horse-shoe magnet
a) P=IV, I= 4 A.
b) = = ; Voltage in
primary = 230V.
c) Using the equation in b) above, : I=
d) Heating of a transformer is independent
of the coating on the wires as it occurs within the wire.
ELECTROMAGNETIC DEVICES QUIZ( 20
A square coil is placed in a uniform magnetic field of flux density 40 mT
Calculate the current in the primary coil, assuming the transformer is 100% efficient