Wednesday, September 2, 2020

Chapter 3 : Electromagnetism- Page 14

Chapter 3 : Electromagnetism

131. The magnetic materials exhibit the properly of magnetisation because of
A. orbital motion of electrons
B. spin of electrons
C. spin of nucleus
D. all of the above

... Answer is ( D)



132. The attraction capacity of electromagnet will increase if the

A. flux density decreases
B. flux density increases
C. core length increases
D. core area increases

... Answer is (B)


133. The magneto-motive force is the two

A. the voltage across the two ends of exciting coil
B. the flow of an electric current
C. the sum of all currents embraced by one line of magnetic field
D. the passage of magnetic field through an exciting coil

... Answer is (C)



134. Which of the following statements is correct?

A. conductivity of ferrites materials is better than ferromagnetic materials
B. The ferromagnetic materials
C. The conductivity of ferixes is very high
B. conductivity of ferrites materials is same as that of ferromagnetic materials

  ... Answer is (A)


135. In which of the material the spin moments associated with two set of atoms are aligned anti-parallel to each other?
Answer is (A)


136. Main causes of noisy solenoids are
strong tendency of fan out of laminations at the end caused by repulsion among magnetic lines of force
B. uneven bearing surface caused by dirt or uneven wear between moving and stationary parts

both of above
D. none of the above

  ... Answer is (C)



137. When a bar magnet is bent at its centre to form the shape of L, its magnetic moment will be

A. 2 times its original value
B. (1/√2) time to original value
C. 1/2 times its original value
D. (
1/3√2)times its original value

... Answer is (B)


138. An air gap is usually inserted in magnetic circuits to

A. increase the flux
B. prevent saturation

increase m.m.f
D. None of the above

... Answer is (B)


139. The relative permeability of a feromagnetic material is

A. more than 10
B. more than 100 or 1000
C.  less than one
D. more than one
  ... Answer is (B)


140.  The unit of magnetic flux is

B. ampe turn/weber

D. weber

  ... Answer is (D)



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