The core of a solenoid is made of material of relative permeability ?r. A small

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Question
The core of a solenoid is made of material of relative permeability ?_r. A small cavity area dA and length dl is cut in the core. If it is desired that flux density in the cavity should be equal to B₀
Options
A. the fields inside and outside the cavity must be equal
B. the field inside the cavity must be made stronger than field outside the cavity
C. the field inside the cavity must be made weaker than the field outside the cavity
D. none of the above

Correct Answer

the field inside the cavity must be made stronger than field outside the cavity

Materials and Components problems

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1. A conductor carries 10 A current in + x direction and is lying in a field having a flux density 0.2 T directed along + z direction. The magnitude of force per metre length and direction are
Options
A. 2 N, + y direction
B. 2 N, - y direction
C. 0.02 N, + y direction
D. 0.02 N, - y direction

2. If a small amount of Cu is added to Ni conductor, then
Options
A. resistivity of Ni will decrease at all temperatures because Cu is a better conductor than Ni
B. residual resistivity of Ni at low temperature will increase as Cu atoms act as defect centres
C. resistivity of Ni will increase at all temperatures as Cu destroys the periodicity of Ni and acts as defects
D. resistivity of Ni remains the same

4. Electrical contact materials used in switches, brushes, relay must possess
Options
A. high thermal conductivity and high melting point
B. low thermal conductivity and low melting point
C. high thermal conductivity and low melting point
D. low thermal conductivity and high melting point

6. Assertion (A): Hall effect is used to determine whether the semi- conductor is p or n type.
Reason (R): Under the influence of field, holes and electrons move in opposite direction.
Options
A. Both A and R are true and R is correct explanation of A
B. Both A and R are true but R is not correct explanation of A
C. A is true but R is false
D. A is false but R is true

9. When a material is in superconducting state and a magnetic field is applied
Options
A. the superconducting property is not affected
B. the superconducting property may be affected and resistivity may increase from zero to a low value
C. the superconducting property may be destroyed
D. the material may become an insulator

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