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Physics Chapter 9 : Topic 13
Coherence
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The term coherence in waves refers to:
Reasoning: Coherent waves maintain a constant phase difference with time, allowing stable interference patterns.
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Two sources are said to be coherent if they produce waves with:
Reasoning: The essential condition for coherence is a constant phase difference between waves.
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Which pair of waves can produce a stable interference pattern?
Reasoning: Stable interference requires a fixed phase relationship, which is provided by coherent sources.
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The phase difference between coherent sources:
Reasoning: Coherent sources can have any constant phase difference, not necessarily zero or $\mathbf{\pi}$.
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Two ordinary bulbs do not produce a stable interference pattern because:
Reasoning: Independent light sources are not coherent because their phases vary randomly.
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A laser produces coherent light because:
Reasoning: Laser light consists of waves that are highly coherent.
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Which of the following is NOT a requirement for coherent sources?
Reasoning: Equal amplitude is not required for coherence; only frequency and phase relationship matter.
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If two waves have the same frequency but their phase difference changes randomly, they are:
Reasoning: A changing phase difference means the waves are not coherent.
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Coherent sources are necessary for observing:
Reasoning: Stable bright and dark fringes require a constant phase difference.
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Two waves have a constant phase difference of $\mathbf{\pi\ /\ 2}$. They are:
Reasoning: Any constant phase difference indicates coherence.
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The main reason independent light sources are not coherent is that:
Reasoning: Independent sources emit waves with unpredictable phase changes.
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Which property must two coherent waves have?
Reasoning: Coherent waves must have the same frequency and a constant phase difference.
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If two coherent waves interfere constructively, their phase difference may be:
Reasoning: Constructive interference occurs when phase difference is an integer multiple of $\mathbf{2\pi}$.
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The most common method to obtain coherent sources in Young’s double slit experiment is:
Reasoning: Light from the same source maintains a fixed phase relationship.
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If the phase difference between two sources changes continuously, the interference pattern will:
Reasoning: Changing phase difference prevents a stable interference pattern.
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Coherence time is the time over which:
Reasoning: Coherence time represents the duration for which waves remain phase-related.
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A pair of sources produces waves with frequencies $\mathbf{500\ Hz}$ and $\mathbf{500\ Hz}$ but random phase changes. These sources are:
Reasoning: Same frequency alone is not enough; constant phase difference is required.
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Which device commonly produces highly coherent electromagnetic waves?
Reasoning: Lasers produce highly coherent light due to stimulated emission.
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Two coherent sound waves must have:
Reasoning: Coherence depends on frequency equality and phase stability.
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In Young’s double slit experiment, the two slits behave as coherent sources because:
Reasoning: Both slits receive light from the same source, maintaining a fixed phase relationship.
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A stable interference pattern cannot be obtained from:
Reasoning: Independent sources have random phase differences.
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If two coherent waves have a phase difference of zero, they are:
Reasoning: Zero phase difference means the waves are in the same phase.
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Coherent sources should have nearly the same frequency because:
Reasoning: Different frequencies cause the phase difference to continuously change.
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The interference pattern produced by incoherent sources is:
Reasoning: Random phase changes cause the pattern to vary with time.
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A student uses two separate torches to perform a light interference experiment. The pattern is not stable because:
Reasoning: Independent torches do not maintain a constant phase difference.
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The coherence of waves is related mainly to their:
Reasoning: Coherence describes the stability of phase difference between waves.
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Which statement correctly describes coherence?
Reasoning: Coherence is the condition necessary for predictable interference.
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A source producing waves with a perfectly constant phase is called:
Reasoning: A coherent source maintains a predictable phase relationship.
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If the phase difference between two waves remains $\mathbf{45}^{\mathbf{o}}$ for a long time, the waves are:
Reasoning: A constant phase difference, regardless of value, indicates coherence.
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The importance of coherence in wave experiments is that it allows:
Reasoning: Coherence makes predictable constructive and destructive interference possible.
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