Transformers MCQs : This section focuses on the "Transformers". These Multiple Choice Questions (MCQs) should be practiced to improve the Transformers skills required for various interviews (campus interview, walk-in interview, company interview), placement, entrance exam and other competitive examinations.
A transformer is used to light 100 W 25 volt lamp from 250 Volt ac mains. The current in the main cable is 0.5 A. Calculate the efficiency of the transformer.
Which among the following is true about transformers?
A. Transformers are used to convert low alternating voltage to a high alternating voltage
B. Transformers are used to convert low alternating current to a high alternating current
C. Transformers are based on the phenomena of mutual electric field
D. Transformers are used only for low alternating voltage
In a step-down transformer, the number of turns in the secondary coil is 20 and the number of turns in the primary coil is 100. If the voltage applied to the primary coil is 120 V, then what is the voltage output from the secondary coil?
A. 24 V
B. 12 V
C. 6 V
D. 18 V
Which of the following is usually taken to make the core of a transformer?
C. Soft iron
D. Hard iron
When does maximum power transfer happen from the source to the load?
A. When the source resistance is greater than the load resistance
B. When the source resistance is less than the load resistance
C. When there is negligible source resistance
D. When the source resistance equals the load resistance
The transformer turns ratio determines
A. the ratio of primary and secondary voltages
B. the ratio of primary and secondary currents
C. the reflected impedance
D. all of the above
Mutual induction is dependent on
A. winding ratios
B. output polarities
C. dc voltage levels
D. current changes
A special transformer used to convert unbalanced signals to balanced signals is the
C. center-tapped transformer
D. step-across transformer
Identify the correct combination for a step-down transformer.
A. k < 1; Vs > Vp, Is > Ip, Ns < Np
B. k > 1; Vs < Vp, Is > Ip, Ns > Np
C. k > 1; Vs > Vp, Is < Ip, Ns > Np
D. k < 1; Vs < Vp, Is > Ip, Ns < Np
What is the formula for the width over 2 limbs?
A. width = Width of largest stamping + Diameter of the transformer
B. width = Diameter + outer diameter of hv windings
C. width = Diameter – outer diameter of hv windings
D. width = outer diameter of hv windings
The coefficient of coupling between two coils is 0.45. The first coil has an inductance of 75 mH and the second coil has an inductance of 105 mH. What is the mutual inductance between the coils?
A. 3.54 mH
B. 7.88 mH
C. 39.9 mH
D. 189.3 mH
A transformer has an efficiency of 60% and works at 5kW. If the secondary voltage is 150 V, then what is the secondary current?
A. 10 A
B. 20 A
C. 30 A
D. 40 A
If the primary power of an ideal transformer having a 2:1 voltage ratio is 100 W, the secondary power is
A. 100 W
B. 50 W
C. 75 W
D. 200 W
Pick out the correct combination for a step-up transformer.
A. k < 1; Vs > Vp, Is > Ip, Ns > Np
B. k > 1; Vs > Vp, Is < Ip, Ns > Np
C. k > 1; Vs > Vp, Is > Ip, Ns > Np
D. k < 1; Vs < Vp, Is > Ip, Ns > Np
Current remains unchanged in a transformer.
What is the formula for the diameter of the single phase core type transformer?
A. D = diameter of circumscribing circle + Width of window
B. D = diameter of circumscribing circle – Width of window
C. D = diameter of circumscribing circle * Width of window
D. D = diameter of circumscribing circle / Width of window
The efficiency of a transformer is the ratio of output power to input power.
Increasing the number of turns of wire on the secondary of a transformer will
A. increase the secondary current
B. decrease the secondary current
C. have no effect on the secondary current
D. increase the primary current
A transformer has
A. primary and secondary windings, both of which are considered inputs
B. primary and secondary windings, both of which are considered outputs
C. a primary winding used as an output and a secondary winding used as an input
D. a primary winding used as an input and a secondary winding used as an output
What is the formula for height of the single phase core type transformer?
A. height = height of the window – height of the yoke
B. height = height of the window + height of the yoke
C. height = height of the window – (2*height of the yoke)
D. height = height of the window + (2*height of the yoke)