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Physics Chapter 9 : Topic 9
Noise-Canceling Headphones
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Noise-canceling headphones work mainly on the principle of:
Reasoning: Noise-canceling headphones use the superposition principle by producing a sound wave that interferes with unwanted noise.
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According to the principle of superposition, when two sound waves overlap, the resultant displacement is:
Reasoning: The superposition principle states that the resultant displacement at any point is the algebraic sum of individual displacements.
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Noise-canceling headphones reduce external noise by producing a sound wave that is:
Reasoning: The headphones generate an anti-noise wave with opposite phase, causing destructive interference with unwanted sound.
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The interference used in active noise cancellation is:
Reasoning: Active noise cancellation depends on destructive interference to reduce the amplitude of unwanted sound.
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If a noise wave has a displacement of $\mathbf{+ \ 4}$ units at a certain instant, the ideal anti-noise wave should have displacement:
Reasoning: For complete cancellation, the anti-noise wave must have equal magnitude and opposite displacement.
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In noise-canceling headphones, the microphone is used to:
Reasoning: Microphones detect surrounding noise so that the headphones can generate an opposite sound wave.
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A noise-canceling headphone produces an anti-noise wave with the same amplitude but a phase difference of $\mathbf{\pi}$. The result is:
Reasoning: A phase difference of $\mathbf{\pi}$ means waves are exactly opposite and cancel each other.
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Why do noise-canceling headphones not completely eliminate all sounds?
Reasoning: Real-world noises have changing frequencies and amplitudes, making perfect cancellation difficult.
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If the external noise and anti-noise wave have equal amplitudes but are in phase, the result will be:
Reasoning: Waves in phase produce constructive interference, increasing amplitude.
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The sound produced by noise-canceling headphones to reduce noise is called:
Reasoning: Anti-noise is a sound wave generated with opposite phase to cancel unwanted noise.
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Which property of waves allows noise cancellation to occur?
Reasoning: Superposition allows two waves to combine and produce either reinforcement or cancellation.
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A noise wave has an amplitude of $\mathbf{10}$ units. For maximum cancellation, the anti-noise wave should have amplitude:
Reasoning: Complete destructive interference requires equal amplitudes.
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The phase difference required between noise and anti-noise waves for cancellation is:
Reasoning: A phase difference of $\mathbf{\pi}$ means one wave’s crest overlaps with the other’s trough.
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Which statement best explains the working of active noise cancellation?
Reasoning: Active noise cancellation uses wave interference rather than simple sound blocking.
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Noise-canceling headphones are more effective for:
Reasoning: Continuous sounds such as engine noise are easier to analyze and cancel.
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If two sound waves combine and their amplitudes cancel, the resulting sound intensity becomes:
Reasoning: Zero resultant amplitude produces minimum sound intensity.
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Which component of noise-canceling headphones generates the anti-noise signal?
Reasoning: The speaker produces the calculated anti-noise wave.
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The principle of superposition is valid for noise cancellation because sound waves are:
Reasoning: Sound waves can occupy the same space and combine according to superposition.
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If the amplitude of the anti-noise wave is smaller than the noise wave, the result will be:
Reasoning: Unequal amplitudes cannot completely cancel; only partial destructive interference occurs.
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A noise-canceling headphone fails to cancel a sound if:
Reasoning: Matching the noise wave in phase causes constructive interference instead of cancellation.
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The main difference between passive and active noise cancellation is that active cancellation:
Reasoning: Active noise cancellation requires electronic generation of an interfering wave.
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A noise wave and anti-noise wave meet at a point. If their displacements are $\mathbf{+ \ 3\ cm}$ and $\mathbf{- \ 2\ cm}$, the resultant displacement is:
Reasoning: By superposition:Resultant displacement $\mathbf{= ( + \ 3) + ( - \ 2) = + \ 1\ cm}$
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Which condition is necessary for effective noise cancellation?
Reasoning: Waves with different frequencies cannot maintain stable destructive interference.
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The energy of sound is not destroyed during noise cancellation because:
Reasoning: Interference changes the distribution of energy but does not violate conservation of energy.
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A student says, “Noise cancellation removes sound energy completely”. The correct explanation is:
Reasoning: Interference reduces sound at certain points but energy conservation is maintained.
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The process used in noise-canceling headphones is an example of:
Reasoning: The anti-noise wave cancels unwanted sound through destructive interference.
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If the phase difference between noise and anti-noise changes from $\mathbf{\pi}$ to $\mathbf{0}$, the headphones will:
Reasoning: A phase difference of $\mathbf{0}$ causes constructive interference, increasing sound amplitude.
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The principle of superposition applies to sound waves because:
Reasoning: Superposition states that overlapping waves combine by adding their displacements.
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A noise-canceling system detects a $\mathbf{500\ Hz}$ noise signal. The anti-noise signal should ideally have:
Reasoning: Effective cancellation requires the same frequency and opposite phase.
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The working principle of noise-canceling headphones demonstrates that:
Reasoning: Noise cancellation is a practical application of wave interference and superposition.
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