Materials and Components – Section 5(Page 2)

Materials and Components – Section 5

11. The direction of force an a conductor carrying current and lying in a magnetic field can be found by using
A. Fleming’s left hand rule
B. Fleming’s right hand rule
C. Cork screw rule
D. Any of the above

Answer: Option A

12.  Assertion (A): Rochelle salt and Barium titanate are both ferroelectric.

Reason (R): Ferroelectric materials exhibit hysteresis effect.

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

Answer: Option B

Explanation:

Both the materials exhibit ferroelectric properties. Hysteresis effect is one of the features of ferroelectric materials.

13.  The units for electric dipole moment are
A. coulombs
B. colomb-metre
C. coulomb/metre
D. coulomb/m2

Answer: Option B

Explanation:

It is product of charge and distance.

14.  The temperature coefficient of resistivity of semiconductors is
A. positive
B. negative
C. may be positive or negative
D. very low

Answer: Option B

Explanation:

Resistance of semiconductors decreases with increase in temperature.

15.  Which of the following is used in automatic control of street lights?
A. Thermistor
B. Photoconductor
C. Transistor
D. Varistor

Answer: Option B

16.  A leaky dielectric has ∈r = ∈rjr. If a field E is applied, the current component in phase with E is proportional to ∈r.
A. True
B. False

Answer: Option A

17.  Assertion (A): In ionic dielectrics, P = Pe + Pi.

Reason (R): In ionic crystals, permanent electric dipole moment is zero.

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

Answer: Option A

Explanation:

In ionic dielectrics μp = ∑i ei ri and Po = 0.

Therefore P = Pe + Pi.

18.  The current flow in a semiconductor is due to
A. holes
B. electrons
C. holes and electrons
D. holes, electrons and ions

Answer: Option C

19. Assertion (A): Relative permittivity is determined by the atomic structure of the material.

Reason (R): Absolute permittivity is determined by the atomic structure of the material.

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

Answer: Option C

20.  Eddy current loss is
A. proportional to frequency
B. independent of frequency
C. proportional to (frequency)2
D. proportional to (frequency)3

Answer: Option C

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