Wednesday, September 2, 2020

Chapter 3 : Electromagnetism- Page 15

Chapter 3 : Electromagnetism

141. Permeability in a magnetic circuit corresponds to ...... in an electric circuit.
A. resistance
B. resistivity
C. conductivity
D. conductance

... Answer is ( C)



142. Point out the wrong statement. magnetic leakage is undesirable in electric machines because it

A. leads to their increased weight
B. produces fringing
C. lowers their power efficiency
D. increases their cost of manufacture

... Answer is (C)


143. Relative permeability of vacuum is

A. 1/4π
B. 4π x 10⁻⁷ H/m

D. I H/m

... Answer is (C)



144. Permanent magnets are normally made of

A. alnico alloys
B. aluminium
C. cast iron
D. wrought iron

  ... Answer is (A)


145. Energy stored by a coil is doubled when its currest is increased by ...... percent.
Answer is (B)


146. The rate of rise of current through an inductive coil is maximum
after one time constant
B. near the final maximum value of current

at 63.2% of its maximum steady value
D. at the start of the current flow

  ... Answer is (D)



147. When both the inductance and resistance of a coil are doubled the value of

A. final steady current is doubled
B. time constant is halved

time constant remains unchanged
D. initial rate of rise of current is doubled

... Answer is (C)


148. The initial rate of rise of current through a coil of inductance 10 H when suddenly connected to a D.C. supply of 200 V is .... A/s

A. 0.05
B. 500

D. 20

... Answer is (D)


149. A material for should have

A. low hysteresis loss
B. high permeability
C. low retentivity
D. high retentivity
  ... Answer is (D)


150.  Conductivity is analogous to

B. inductance

D. resistivity

  ... Answer is (A)



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