Q25.An observer is riding on a bicycle and moving towards a hill at 18 km h-1. He hears a sound from a source at some distance behind him directly as well as after its reflection from the hill. If the original frequency of the sound as emitted by source is 640 Hz and velocity of the sound in air is 320 m s-1, the beat frequency between the two sounds heard by observer will be _____ Hz.
What This Question Tests
This multi-step problem requires applying the Doppler effect formula twice: first for direct sound and second for reflected sound (treating the hill as a moving source and observer, then the observer as moving), then calculating the beat frequency.
Concepts Tested
Formulas Used
f' = f_0 * (v ± v_o) / (v ± v_s)
f_beat = |f_1 - f_2|
📚 NCERT Sections This Tests
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11.8 — Light Of Frequency 7.21 × 1014 Hz Is Incident On A Metal Surface.
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11.8 Light of frequency 7.21 × 1014 Hz is incident on a metal surface. Electrons with a maximum speed of 6.0 × 105 m/s are ejected from the surface. What is the threshold frequency for photoemission of electrons?
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2.5 A parallel plate capacitor with air between the plates has a capacitance of 8 pF (1pF = 10–12 F). What will be the capacitance if the distance between the plates is reduced by half, and the space between them is filled with a substance of dielectric constant 6?
📋 Question Details
- Chapter
- Waves & Sound
- Topic
- Doppler Effect
- Year
- 2022
- Shift
- 25 Jul Shift 1
- Q Number
- Q25
- Type
- Numerical
- NCERT Ref
- Class 11 Physics Ch 15: Waves
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