When a source of sound moves towards a stationary observer, the apparent frequency: MCQ with Answer and Explanation

When a source of sound moves towards a stationary observer, the apparent frequency:
A. Remains same
B. Becomes zero
C. Increases
D. Decreases
Answer: Option C
Solution (By JKSSB Mock Tests)
This is the Doppler effect: when source moves toward observer, wavefronts compress, decreasing wavelength, thus increasing apparent frequency (f' = f·v/(v - v_s), where v is sound speed, v_s source speed). Conversely, receding source decreases frequency. This applies to all waves (light, sound). Memory aid: 'Approaching = higher pitch (frequency); Receding = lower pitch'. Competitive exams often test qualitative understanding before formula application. Always identify motion direction relative to observer for sign conventions in numerical problems.

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Practice More Physics Questions

Question #1
The principle of conservation of linear momentum is a consequence of:
A. Law of conservation of energy
B. Newton's first law
C. Newton's second law
D. Newton's third law

Correct Answer: Option D


Explanation:
Conservation of linear momentum follows from Newton's third law (action-reaction pairs) and second law. For an isolated system, internal forces cancel in pairs (third law), so net force = 0, thus dp/dt = 0 (second law), meaning momentum constant. While derivable from second law with third law, the direct foundational link is third law. Memory aid: 'Momentum conservation ⇔ no external force ⇔ internal forces cancel (third law)'. This conceptual question tests mechanics fundamentals, crucial for competitive exams. Always distinguish conservation laws: momentum (from spatial symmetry), energy (from time symmetry).

This question belongs to: Science Physics
Question #2
The maximum height attained by a projectile is H when angle of projection is 30°. For angle 45° and same u, height will be
A. 2H/√3
B. 2H
C. 3H/2
D. H/√3

Correct Answer: Option B


Explanation:
H ∝ sin²θ. H₁ ∝ sin²30 = 1/4. H₂ ∝ sin²45 = 1/2. Ratio H₂/H₁ = (1/2)/(1/4) = 2. So H₂ = 2H.

This question belongs to: Science Physics
Question #3
The angle of incidence is equal to angle of reflection is the law of
A. Reflection
B. Diffraction
C. Refraction
D. Dispersion

Correct Answer: Option A


Explanation:
Law of reflection.

This question belongs to: Science Physics