What is the formula for efficiency of a machine?

Last Updated: 25 Jun 2026

What is the formula for efficiency of a machine? Here, the relevant answer is “Output/Input × 100%.” A sound solution relies on the governing concept rather than a memorised option letter, because option order may change in another paper. While reading a question, first note whether it asks for a definition, SI unit, formula, direction, cause, effect, or practical use. The distractors in this question—Input/Output × 100%, Work done/Time, Force × Distance—do not satisfy the exact condition stated. Revise the definition, symbol, SI unit, formula, and one everyday example as a single learning set. The final selection must agree with the explanation and marked answer: Output/Input × 100%.

AInput/Output × 100%

BOutput/Input × 100%

CWork done/Time

DForce × Distance

Correct Answer: Output/Input × 100%Your Answer: B

Explanation

— the scientifically appropriate response is Output/Input × 100%. Option-wise review: Output/Input × 100% is correct under the condition given in the stem. Input/Output × 100% is incorrect because it describes a different quantity or phenomenon and does not meet the stated condition. Work done/Time is also incorrect; although it may be a valid physics term, its definition or application is not the one asked here. Force × Distance is incorrect because it fails the governing relation or characteristic relevant to this case. Therefore, option B, Output/Input × 100%, is factually and logically consistent with the question. Efficiency = (Output/Input) × 100%. No machine is 100% efficient due to friction.

Important Notes

Read the complete stem before looking at the options. Identify whether the demand is a definition, unit, formula, direction, cause, effect, image characteristic, or device principle. In this record, the confirmed answer is Output/Input × 100%.
Physics answers are condition-dependent. The same lens, force, circuit, wave, or thermodynamic system can behave differently when distance, medium, temperature, direction, or boundary conditions change. Preserve every qualifier in the question.
Learn each concept as a five-part card: definition; common symbol; SI unit; principal equation; and one real-life application. This works for mechanics, heat, optics, sound, electricity, magnetism, and modern physics.
Use dimensional consistency as a quick check for formulas. Both sides of a valid physical equation must have the same dimensions. Units can eliminate distractors quickly, although a dimensionally correct option must still satisfy the actual law.
Do not interchange closely related terms: mass and weight; distance and displacement; speed and velocity; heat and temperature; reflection and refraction; real and virtual image; current and potential difference; power and energy. Such pairs generate common SSC distractors.

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FAQ

SSC CGL Physics FAQs

Common questions and clear answers for this topic.

How many physics questions usually appear in the SSC CGL exam?

Physics typically makes up a small portion of the General Science questions, usually focused on concepts rather than numerical problems.

Which physics topics are most important for SSC CGL?

Basic mechanics, heat, sound and light, and electricity and magnetism are the areas that come up most consistently across previous papers.

Do I need to solve numerical problems for SSC CGL physics?

Rarely. Most questions are conceptual and test everyday understanding rather than calculation skills.

Is NCERT physics enough for SSC CGL preparation?

NCERT textbooks from classes 9 and 10 build a strong enough conceptual base for most of what SSC CGL asks.

How can I make physics concepts easier to remember for SSC CGL?

Connecting concepts to everyday observations, like why a thermos keeps tea warm, makes them far easier to recall than memorizing definitions.

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