Question

Retardation curve is ______________

(a) Starting from origin

(b) Starts from some positive value and increasing

(c) Starts from some positive curve and stays constant

(d) Starts from some positive value and decreases

This question was posed to me in an interview for internship.

This interesting question is from Swinburne’s Test in portion Efficiency and Testing of DC Machines

Answer 1

The correct answer is (d) Starts from some positive value and decreases

To explain: Retardation curve is a plot of speed vs. time at various retarding speeds. Thus, curve starts at some positive value and shows exponentially decaying nature with time. From various values of speed we calculate windage and friction loss at each point.