All Free Electrical Engineering MCQs with Answers

• A. copper alloy
• B. carbon
• C. tungsten alloy
• D. stainless steel alloy

Explanation: Tungsten-alloy elements can withstand temperatures around 2250°C because tungsten has a very high melting point and retains strength at…

• A. tungsten
• B. graphite
• C. silver
• D. copper

Explanation: Graphite is used for direct-arc furnace electrodes because it conducts current and withstands the extremely high arc temperature.

• A. Current
• B. Voltage
• C. Power factor
• D. All of the above

Explanation: A direct-arc furnace operates with very high current and comparatively low voltage to produce the arc and intense heat.

• A. To achieve better heating
• B. To increase the life of roof refractory
• C. To have better stirring action
• D. To reduce problem of oxidation
• E. All of the above

Explanation: A short arc concentrates heat near the charge, reduces radiation toward the roof, limits refractory damage and oxidation, and supports…

• A. as an insulator
• B. as a device for power factor improvement
• C. for dielectric heating
• D. for induction heating

Explanation: Mica has high dielectric strength and good heat resistance, so it is used as an electrical insulator in presses and heating equipment.

• A. Coreless transformers
• B. Current transformers
• C. Motor-generator set
• D. Multi-phase transformer

Explanation: Older induction furnaces obtain the required high-frequency supply from a motor-generator set, whose generator is designed for the…

• A. Insulating materials
• B. Conducting materials which are magnetic
• C. Conducting materials which are non-magnetic
• D. Conducting materials which may or may not be magnetic

Explanation: Induction heating requires electrical currents induced in a conductor, so insulating materials cannot be heated directly by this method.

• A. By disconnecting some of the heating elements
• B. By varying the operating voltage
• C. By varying the current through heating elements
• D. By any of the above method

Explanation: An arc furnace’s heat input depends on its electrical power, approximately given by VI.

• A. phase angle
• B. frequency
• C. current
• D. voltage

Explanation: Induction heating uses a frequency much higher than ordinary power frequency to induce strong eddy currents and concentrate heating near…

• A. oxidizing
• B. deoxidising
• C. reducing
• D. neutral

Explanation: A conventional resistance furnace operates with air around its heating elements, giving it an oxidizing atmosphere.

• A. Water
• B. Steam
• C. Sold ice
• D. Melting ice

Explanation: Solid ice has a thermal conductivity of roughly 2.2 W/m·K, higher than water and much higher than steam.

• A. bodies are kept in vacuum
• B. bodies are immersed in water
• C. bodies are exposed to thermal radiations
• D. temperatures of the two bodies are identical

Explanation: Conduction is driven by a temperature gradient, so no net heat is conducted between bodies at identical temperatures.

• A. inside boiler furnaces
• B. during melting of ice
• C. through the surface of the insulted pipe carrying steam
• D. from refrigerator coils to freezer of a refrigerator

Explanation: Inside a boiler furnace, heat reaches the surroundings by conduction through solids, convection through moving hot gases, and radiation…

• A. temperature of the two bodies must be different
• B. both bodies must be solids
• C. both bodies must be in contact
• D. at least one of the bodies must have some source of heating

Explanation: Net heat transfer requires a temperature difference, and the bodies need not be solids or in direct contact because radiation and…

• A. transmits all incident radiations
• B. absorbs all incident radiations
• C. reflects all incident radiations
• D. absorbs, reflects and transmits all incident radiations

Explanation: A perfect black body absorbs 100% of the radiation incident on it, so its absorptivity is unity.

• A. ferromagnetic material
• B. diamagnetic material
• C. paramagnetic material
• D. conducting material

Explanation: Diamagnetic materials develop an induced magnetic moment opposite to the applied field, so they are slightly repelled.

• A. direction of magnetic field due to current carrying conductor
• B. direction of flux in a solenoid
• C. direction of force on a current carrying conductor in a magnetic field
• D. polarity of a magnetic pole

Explanation: Fleming's left-hand rule gives the direction of force or motion on a current-carrying conductor placed in a magnetic field.

• A. it corrodes easily
• B. it has high permeability
• C. it has high specific gravity
• D. it has low permeability

Explanation: Steel has comparatively low permeability, so it requires a strong magnetising force to establish flux in it.

• A. the magnetic lines of force will bend away from their usual paths in order to go away from the piece
• B. the magnetic lines of force will bend away from their usual paths in order to pass through the piece
• C. the magnetic field will not be affected
• D. the iron piece will break

Explanation: Iron has high permeability, offering an easier path for magnetic flux than the surrounding air.

• A. flux density
• B. susceptibility
• C. relative permeability
• D. none of the above

Explanation: Magnetic susceptibility is defined as the ratio of intensity of magnetisation M to magnetising field intensity H, written as χ = M/H.