Question: Those magnetic materials are best suited for making armature and transformer cores which have ________ permeability and ________ hystersis loss.

• 1. high, high
• 2. low, high
• 3. high, low
• 4. low, low

Question: A material for good magnetic memory should have____________?

• 1. low hysteresis loss
• 2. high permeability
• 3. low retentivity
• 4. high retentivity

Question: If the area of hysteresis loop of a material is large, the hysteresis loss in this material will be____________?

• 1. zero
• 2. small
• 3. large
• 4. none of the above

Question: 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__________Vs.

• 1. 50
• 2. 20
• 3. 0.05
• 4. 500

Question: The rate of rise of current through an inductive coil is maximum_____________?

• 1. at 63.2% of its maximum steady value
• 2. at the start of the current flow
• 3. after one time constant
• 4. near the final maximum value of current

Question: Permanent magnets are normally made of_____________?

• 1. alnico alloys
• 2. aluminium
• 3. cast iron
• 4. wrought iron

Question: The unit of magnetic flux is______________?

• 1. henry
• 2. weber
• 3. ampereturn/weber
• 4. ampere/metre

Question: Point out the wrong statement. Magnetic leakage is undesirable in electric machines because it___________?

• 1. lowers their power efficiency
• 2. increases their cost of manufacture
• 3. leads to their increased weight
• 4. produces fringing

Question: An air gap is usually inserted in magnetic circuits to____________?

• 1. increase m.m.f.
• 2. increase the flux
• 3. prevent saturation
• 4. none of the above

Question: In a magnetic material hysteresis loss takes place primarily due to___________?

• 1. rapid reversals of its magnetisation
• 2. flux density lagging behind magnetising force
• 3. molecular friction
• 4. it high retentivity