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

Question: Hysteresis loss least depends on____________?

• 1. volume of material
• 2. frequency
• 3. steinmetz coefficient of material
• 4. ambient temperature

Question: The unit of reluctance is_____________?

• 1. metre/henry
• 2. henry/metre
• 3. henry
• 4. 1/henry

Question: Reciprocal of reluctance is_______________?

• 1. reluctivity
• 2. permeance
• 3. permeability
• 4. susceptibility

Question: The property of a material which opposes the creation of magnetic flux in it is known as_____________?

• 1. reluctivity
• 2. magnetomotive force
• 3. permeance
• 4. reluctance

Question: Silicon steel is used in electrical machines because it has_____________?

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