Download S.5 Phy Induction hw1_V1

STCC
S.5 Phy
Electromagnetic Induction hw1
submit by 23/4
Mr. Yau
1. The figure below shows a solenoid of length 80 cm. The solenoid has 500 turns and it carries a current of
50 mA. (Given the permeability of free space μ0 = 4  10–7 T m A–1)
(a) Find the magnitude of the magnetic field at the centre O of the solenoid.
(2 marks)
(b) What is the major assumption in (a)?
(1 mark)
(c) A search coil of 5000 turns and an area of 1.5 cm2 is placed at O. The plane of the coil is
perpendicular to the magnetic field. Calculate the magnetic flux linkage through the search coil.
(2 marks)
2.
soft-iron
(a) Describe the direction of the pointer of the galvanometer when the magnet swings towards and away
the coil, as shown in the above figure.
(2 marks)
(b) The magnet finally stops right above the coil. What happens to the pointer of the galvanometer then?
Explain briefly.
(2 marks)
3.
A wire of length 16 cm is bent to a circular wire frame and placed in a uniform magnetic field of 0.5 T
pointing into the paper. Its shape is then changed into a square in 2 s.
(a) What is the direction of the induced current in the frame through this period? Explain your answer.
(3 marks)
(b) Calculate the average induced e.m.f. in the frame in this period.
(3 marks)
4.
A magnetic field passes perpendicularly through a circular coil of radius 12 cm. The magnetic field
changes with time t as show below.
B/T
0.5
t/s
2
4
6
Calculate the magnitude of the induced e.m.f. in the coil in each of the following time intervals:
(a) t = 0 to t = 2 s;
(b) t = 2 s to t = 4 s; and
(c) t = 4 s to t = 6 s.
5.
(4 marks)
A metal rod is moving at a uniform speed of 55 cm s–1on two parallel metal rails as shown below. A
magnetic field of 0.35 T is pointing out of the paper. The separation between the upper and the lower rails
is 25 cm.
55 cm–1
B
(a) Find the magnitude of the induced e.m.f. in the rod.
(3 marks)
(b) Find the current through the rod if the resistance of rod is 18 Ω. Assume that the resistance of the
metal rails is negligible.
(2 marks)
(c) What is the rate of heat generated by the metal rod?
(2 marks)
(d) In order to keeps the rod moving at the same speed, what is the direction and magnitude of the
external force acting on the rod?
(3 marks)
6.(Bonus) A solenoid of diameter 8 cm and length 1 m has 500 turns of wire. A square coil, of length 1 cm and
negligible resistance, is connected by a pair of twisted wires to a 70- resistor.
coil
solenoid
IS
70 
The graph below shows how the current IS in the solenoid varies with time t.
IS / A
I0
0
0.2
0.6
1
t/s
The induced current IC in the coil is 0.01 A in the first 0.2 s.
(Given the permeability of free space μ0 = 4π  10–7 T m A–1)
(a) Find the value of the maximum current through the solenoid, I0.
(4 marks)
(b) State two assumptions in your calculation.
(2 marks)
(c) Find the induced current IC in the coil
(i)
from t = 0.2 s to t = 0.6 s;
(ii) from t = 0.6 s to t = 1 s.
Hence, complete the above graph.
(6 marks)