# Design of Electrical Machines Questions and Answers – Design of Output Equations

This set of Design of Electrical Machines Multiple Choice Questions & Answers (MCQs) focuses on “Design of Output Equations”.

1. With what component is the output equation of DC machines related to?
a) power
b) voltage
c) current
d) losses

Explanation: The output equation generally deals with the power generated in the machine. Power of the machine relates the voltage and current flowing though the machine.

2. What can be found out using the output equation of the DC machine?
a) main dimensions
b) angle of rotation
c) losses
d) efficiency

Explanation: The output equation of DC machine is mainly used to obtain the main dimensions of the machine. Main dimensions are very important in calculation of various factors related to the machine.

3. What are the components of the main dimensions of output equation of DC machine?
a) diameter
b) length
c) diameter and length
d) voltage

Explanation: Main dimensions generally deal with the diameter of the machine. It also deals with the length of the machine.

4. What is the starting equation for deriving the output equation of DC Machines?
a) P = Generated Emf + Armature Current
b) P = Generated Emf – Armature Current
c) P = Generated Emf * Armature Current
d) P = Generated Emf / Armature Current

Explanation: The first equation for deriving the output equation of DC machines starts from this equation. The generated emf is multiplied along with the armature current.

5. The output equation of the DC machines can be used to calculate the speed of the machine.
a) true
b) false

Explanation: The output equation can be used to calculate the speed of the machine. The output coefficient of the DC machine, diameter and length of the conductors must be provided.

6. What is the output equation of DC machine?
a) Output power = Output Coefficient of the machine* Diameter2 * Length * Speed in rpm
b) Output power = Output Coefficient of the machine* Diameter2 * Length * Speed in rps
c) Output power = Output Coefficient of the machine* Diameter2 * Length / Speed in rps
d) Output power = Output Coefficient of the machine* Diameter2 * Length / Speed in rpm

Explanation: While calculating the output power of the DC machine, the coefficient of output equation, the diameter of the conductor, the length of the conductor and the speed is required. Speed should be in rotations per second only.

7. What are the terms related to deriving the output equation of the DC machine?
c) thermal coefficient of machine

Explanation: For deriving the output equation, both the specific magnetic and electric loading formulas are made use of. By substituting the 2 formulas, the output equation is derived.

8. For a DC generator, what is the output power equation?
a) Output power = Generated Power * efficiency
b) Output power = Generated Power / efficiency
c) Output power = Generated Power – efficiency
d) Output power = efficiency / generated power

Explanation: For DC generator, the efficiency also taken into account, while calculating the final output power value. Whereas, the same is not considered while calculating for motor.

9. For a DC motor, what is the output power equation?
a) Output power = Generated Power / efficiency
b) Output power = Generated Power * efficiency
c) Output power = Generated Power
d) Output power = Generated Power + efficiency

Explanation: Output power = Generated Power / efficiency – For DC Generator
Output power = Generated Power – For DC Motor.

10. For a DC generator, given D = 0.35 m, L = 0.21 m, Coefficient of output = 108.5, efficiency = 0.9, speed = 1400 rpm. What is the output power of the DC generator?
a) 65.12 W
b) 72.35 KW
c) 72.35 W
d) 65.12 KW

Explanation: Generated power = 108.5 * 0.35 * 0.35 * 0.21 * (1400/60) = 65.12 KW
Output Power = Generated Power / Efficiency = 65.12 / 0.9 = 72.35 KW.

Sanfoundry Global Education & Learning Series – Design of Electrical Machines.

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