Ultrasonic waves have frequency MCQ with Answer and Explanation

Ultrasonic waves have frequency
A. Greater than 20 MHz
B. Greater than 20 kHz
C. 20 Hz to 20 kHz
D. Less than 20 Hz
Answer: Option B
Solution (By JKExamLibrary)
Above 20 kHz is ultrasound.

This question belongs to: Science Physics

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Practice More Physics Questions

Question #1 Report Error
The mirror used as rear-view mirror in vehicles is
A. Parabolic mirror
B. Convex mirror
C. Concave mirror
D. Plane mirror

Correct Answer: Option B


Explanation:
Convex mirror gives wider field of view, always forms virtual, erect, diminished image. Allows driver to see larger area. Concave can magnify but field narrow. Plane gives normal view but limited field.

This question belongs to: Science Physics
Question #2 Report Error
According to Wien's Displacement Law, if the absolute temperature of a radiating black body is doubled, the wavelength corresponding to maximum spectral emissive power will:
A. Increase four times
B. Double
C. Remain unchanged
D. Halve

Correct Answer: Option D


Explanation:
Wien's Displacement Law states that the wavelength at which a black body emits maximum radiation (lambda_m) is inversely proportional to its absolute temperature (T). lambda_m * T = b (Wien's constant). If the temperature T is doubled (2T), the peak wavelength lambda_m must strictly halve to maintain the constant product.

This question belongs to: Science Physics
Question #3 Report Error
The specific charge (e/m) of an electron was first measured by:
A. Millikan
B. Rutherford
C. Bohr
D. Thomson

Correct Answer: Option D


Explanation:
J. J. Thomson measured the specific charge (e/m) of electrons in 1897 using cathode ray tube experiments with electric and magnetic fields. Millikan later measured the charge e (oil drop experiment), allowing mass calculation. Rutherford discovered nucleus; Bohr developed atomic model. Memory aid: 'Thomson = e/m; Millikan = e'. This history-based question tests knowledge of experimental physics milestones, frequently appearing in competitive exams. Always link scientists to their specific measurements: Thomson (e/m), Millikan (e), Chadwick (neutron).

This question belongs to: Science Physics