Motor Efficiency and Friction Losses Steps:

• Define efficiency as useful output power divided by input power.
• Identify friction as a key energy loss in motors, converting electrical energy to unwanted heat.
• Evaluate options: only reducing friction minimizes losses without altering input or safety features.
• Confirm that lower losses mean higher efficiency for the same electrical input.

Why B is correct:

• Efficiency η = (useful work / total energy input) × 100%; reducing friction lowers mechanical losses, increasing useful output per unit input per the law of energy conservation.

Why the others are wrong:

• A: Increases energy losses as heat, decreasing efficiency.
• C: Allows higher current but does not reduce internal losses like friction.
• D: May cause premature fuse blowing, interrupting operation without improving efficiency.

Final answer: B