1.(A)Define the Term Magnetic Flux Density.(2)

GHS

PHYSICS P510/2

MAGNETISM REVISION QUESTIONS.

AUGUST 2012

1.(a)Define the term magnetic flux density.(2)

(b)

S β

0.01mR

A rectangular coil PQRS of 100 turns and cross section area of is carrying a current of 5A.The coil is placed in a magnetic field of flux density B of 0.2T as shown above. The side SR is 0.01m and the force 0.6N acts on it.

Calculate

(i)the angle β(3)

(ii)the torque on the coil.(3)

(c)

A wire carrying a current of 2.4A is placed inside a long solenoid of 2000 turns per metre as shown above. The part of the wire XY of length 1.1m experiences a force of 0.03N.Find

(i)the current in the solenoid.(3)

(ii)the force on an electron which moves in the wire with a speed

of (2)

(d) (i) Draw a labelled diagram of the moving coil galvanometer and explain how it works. (5)

(ii) A moving coil galvanometer of resistance 20Ω gives a full scale deflection when a current of 5mA passes through it. How can it be converted to an ammeter which can measure a maximum current of 6A. (2)

2.(a)State the laws of electromagnetic induction.(2)

(b)(i)With the aid of a labelled diagram, describe how a simple a.c generator works. (6)

(ii)State the factors which determine the magnitude of the voltage generated by a simple a.c generator. (2)

(iii)What are the main energy losses in a practical a.c generator and how are these minimised? (2)

(c )A coil of 50 turns is wound tightly around the middle of an air cored solenoid of 1000turns per metre and mean diameter 7.0cm. An alternating current is passed through the solenoid.

(i)Calculate the amplitude of the voltage which develops across the terminals of the coil. (6)

(ii)Using the same axes sketch graphs to show the variation with time of the voltage induced across the terminals of the coil and the current, I, through the solenoid. (2)

3.(a)Explain the main difference between magnetic flux and magnetic flux density. (2)

(b)(i)Two long conductors carrying a current are placed parallel to each other in a vacuum at a distance d metres apart. Derive an expression for the force per unit length acting on each wire when a current amperes flows through one through the other. (5)

(ii)How does the expression in (i) lead to the definition of the ampere?(2)

(c )A straight horizontal conducting rod of length 0.45m and mass 60g is suspended by two vertical wires at its ends. A current of 5.0A is set up in the rod through the wires.

(i)what magnetic field should be set up normal to the conductor in order that the tension in the wires is zero? (2)

(ii)What will be the total tension in the wires if the direction of current is reversed keeping the magnetic field same as before?(g= 9.81ms-2). (3)

(d)(i)Sketch the magnetic field pattern around a vertical current carrying straight wire in the earth’s magnetic field. (2)

(ii)Use the sketch in d(i) above to explain the term neutral point in a magnetic field. (1)

(e)A coil of cross section area is to be used to produce a uniform magnetic flux density of .

(i)Where will the magnetic field be uniform?(1)

(ii)Calculate the total flux through the coil.(2)