The phenomenon of apparent change in frequency due to relative motion between source and observer is called MCQ with Answer and Explanation

The phenomenon of apparent change in frequency due to relative motion between source and observer is called
A. Echo
B. Resonance
C. Diffraction
D. Doppler effect
Answer: Option D
Solution (By JKExamLibrary)
Doppler effect: observed frequency higher when approaching, lower when receding. Applications: radar speed guns, astronomical redshift/blueshift, echocardiography. Echo is reflection. Resonance is vibration matching. Diffraction is bending.

This question belongs to: Science Physics

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Question #1 Report Error
Assertion (A): When ice floats in water, its approximately 1/10th volume remains outside the water. Reason (R): The density of ice is approximately 10% less than the density of water.
A. Both A and R are true but R is NOT the correct explanation of A.
B. Both A and R are true and R is the correct explanation of A.
C. A is true but R is false.
D. A is false but R is true.

Correct Answer: Option B


Explanation:
The density of ice is about 900 kg/m³ (0.9 g/cm³), while pure water is 1000 kg/m³ (1.0 g/cm³). According to the principle of floatation, the fraction of volume submerged is the ratio of densities: ρ_ice / ρ_water = 0.9. This means 90% is submerged, leaving exactly 10% (1/10th) exposed above the surface. Reason R explains Assertion A.

This question belongs to: Science Physics
Question #2 Report Error
Two electric bulbs rated 60W, 220V and 100W, 220V are connected strictly in series across a 220V supply. Which bulb will glow brighter?
A. Both will glow with equal brightness.
B. Neither will glow.
C. 60W bulb
D. 100W bulb

Correct Answer: Option C


Explanation:
Resistance of a bulb is R = V^2 / P. The 60W bulb has a higher resistance than the 100W bulb. When connected in series, the exact same current (I) flows through both. The power consumed (which determines brightness) is given by P = I^2R. Since the 60W bulb has higher resistance (R), it consumes more power and glows brighter.

This question belongs to: Science Physics
Question #3 Report Error
The amount of heat required to raise temperature of 1 g water by 1°C is
A. Both B and C
B. 1 cal
C. 1 J
D. 4.2 J

Correct Answer: Option A


Explanation:
1 cal = 4.186 J ≈ 4.2 J. So both are correct. However option D covers both. I'll set D as correct.

This question belongs to: Science Physics