Question Bank • QB_IDE_004 MCQ • 1 Mark

Section 5: Irrigation and Drainage Engineering

Wells and Pumps

Subtopic: Pump characteristics

Question Statement:

According to the affinity laws for a centrifugal pump with a fixed impeller diameter, if the pump rotational speed $N$ is doubled, the head $H$ developed by the pump will:

Options:

  • (A) Double ($2\times$)
  • (B) Increase by 4 times ($4\times$)
  • (C) Increase by 8 times ($8\times$)
  • (D) Remain unchanged

Answer Key:

B

Step-by-Step Solution & Explanation

Centrifugal pump affinity laws state: 1. Discharge: $Q \propto N$ 2. Head: $H \propto N^2$ 3. Brake Power: $P \propto N^3$ When speed is doubled ($N_2 = 2N_1$): $\frac{H_2}{H_1} = \left(\frac{N_2}{N_1}\right)^2 = 2^2 = 4$
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