What is the Doppler effect?

Last Updated: 25 Jun 2026

What is the Doppler effect? Here, the relevant answer is “Apparent change in frequency due to relative motion.” 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—Change in amplitude of sound, Change in wave speed, Change in wavelength only—do not satisfy the exact condition stated. The final selection must agree with the explanation and marked answer: Apparent change in frequency due to relative motion.

AChange in amplitude of sound

BApparent change in frequency due to relative motion

CChange in wave speed

DChange in wavelength only

Correct Answer: Apparent change in frequency due to relative motionYour Answer: B

Explanation

— the scientifically appropriate response is Apparent change in frequency due to relative motion. Option-wise review: Apparent change in frequency due to relative motion is correct under the condition given in the stem. Change in amplitude of sound is incorrect because it describes a different quantity or phenomenon and does not meet the stated condition. Change in wave speed is also incorrect; although it may be a valid physics term, its definition or application is not the one asked here. Change in wavelength only is incorrect because it fails the governing relation or characteristic relevant to this case. Therefore, option B, Apparent change in frequency due to relative motion, is factually and logically consistent with the question. The Doppler effect is the apparent change in frequency/wavelength of a wave due to relative motion between source and observer.

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 Apparent change in frequency due to relative motion.
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.
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.
Eliminate Change in amplitude of sound, Change in wave speed, Change in wavelength only here because none fulfils the exact requirement of the stem. The final answer and correct-index field must point to option B.

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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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