The instrument used to measure the wavelength of light is: MCQ with Answer and Explanation

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The instrument used to measure the wavelength of light is:

A. Spectrometer

B. Microscope

C. Interferometer

D. Telescope

Answer: Option A

Solution (By JKSSB Mock Tests)

Spectrometer measures wavelengths of light using diffraction gratings or prisms to disperse light and angular measurements. Interferometer (D) can also measure wavelength but spectrometer is the standard instrument for spectral analysis. Microscope and telescope magnify images, not measure wavelength. Memory tip: 'Spectrometer = wavelength measurement via dispersion; used in spectroscopy'. This instrument-application question tests practical physics knowledge, frequently examined in competitive exams. Always associate instruments with their primary function; competitive exams often test context-specific uses.

This question belongs to: Science Physics

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Question #1

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Escape velocity of a body from Earth is 11.2 km/s. For a planet with mass 9 times Earth and radius same, escape velocity is

A. 3.73 km/s

B. 11.2 km/s

C. 33.6 km/s

D. 22.4 km/s

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Correct Answer: Option C

Explanation:
v_esc ∝ √M. M'=9M => v'=3×11.2=33.6 km/s.

This question belongs to: Science Physics

Question #2

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A body is moving with uniform speed in a circular path. Which statement is correct?

A. Acceleration is zero

B. Velocity is constant

C. No force acts on the body

D. Acceleration is directed towards the center

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Correct Answer: Option D

Explanation:
In uniform circular motion, speed is constant but velocity direction changes continuously, requiring centripetal acceleration directed toward the center (a = v²/r). By Newton's second law, a centripetal force must act. Velocity isn't constant (direction changes); acceleration isn't zero; force is required. Memory tip: 'Uniform circular motion: constant speed, changing velocity, center-seeking acceleration'. This conceptual question tests understanding of circular dynamics, crucial for mechanics in competitive exams. Always distinguish speed (scalar) from velocity (vector) in motion analysis.

This question belongs to: Science Physics