Wednesday, September 2, 2020

Chapter 3 : Electromagnetism- Page 17

Chapter 3 : Electromagnetism

161. A ferritecore has less eddy current loss than an iron core because
A. ferrites have low permeability
B. ferrites have high hysteresis
C. ferrites have high resistance
D. ferrites are magnetic

... Answer is (A)



162. A ferromagnetic core subjected to cycles of magetisation will exhibit hysteresis when the cycle is

A. rotating
B. alternating
C. pulsating
D. any of the above

... Answer is (D)


163. In order to minimise loss due to hysteresis, the magnetic material should have

A. large B-H loop area
B. high retentivity

high resistivity
D. low hysteresis co-efficient

... Answer is (D)



164. Hysteresis loss least depends on

A. Steinmetz co-efficient of material
B. ambient temperature
C. volume of material
D. frequency

  ... Answer is (B)


165. Laminated cores, in electrical machines, are used to reduce
Answer is (B)


166. The area of hysteresis loss is a measure of
B. permeance
C. energy loss per cycle
D. magnetic flux

  ... Answer is (C)



167. Permeance is to reluctance as conductance is to

A. capacitance
B. resistance

ampere turns
D. inductance

... Answer is (B)


168. According to steinmetz hysteresis law,hysteresis loss in a material is proportional to

A. B^(3.6)
B. B
C. B^(2.6)
D. B^(1.6)

... Answer is (D)


169. The transformer cores operating at microwavefrequency range, are usually made of

A. carbon
B. copper
C. silicon steels
D. ferrites
  ... Answer is (D)


160.  In free space with ρ=0, Poissons's equation is

continuity equation (.J=0)
B. Laplacian equation (
Maxwell curl equation (∇ x V=0)  

D. Maxwell divergence equation (∇B=0)

  ... Answer is (B)



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