Waves MCQs | Physics MCQs

A compression is a region of high density/pressure, similar to a crest (maximum positive displacement). A rarefaction is a region of low density/pressure, similar to a trough (maximum negative displacement).

When a wave enters a rarer (less dense) medium, its speed generally increases. Since frequency remains constant, and v=fλ, the wavelength must increase.

The energy transported by a wave is proportional to the square of its amplitude. A wave with twice the amplitude carries four times the energy.

This is the simplest standing wave pattern that can fit in a pipe open at both ends. This pattern (Antinode-Node-Antinode) spans half a wavelength.

Solids are generally much more elastic and denser than liquids or gases. The increase in the elastic modulus is far more significant than the increase in density, leading to a much higher speed of sound (v=√(E/ρ)).

Humid air is less dense than dry air because water molecules (H₂O) have less mass than the nitrogen (N₂) and oxygen (O₂) molecules they replace. Since speed is inversely proportional to the square root of density, lower density means higher speed.

This is the definition of coherence. The phase relationship between the waves does not change over time, which is necessary to observe a stable interference pattern.

Loudness is the human perception of sound intensity, which is directly related to the amplitude of the sound wave. A larger amplitude corresponds to a louder sound.

Polarization involves restricting the orientation of wave oscillations to a single plane. This is only possible if the oscillations are perpendicular to the direction of wave travel, which is the definition of a transverse wave.

The frequency of a vibrating string is proportional to the square root of the tension (f ∝ √T). Therefore, if the tension is quadrupled, the frequency becomes √4 = 2 times the original.

A pulse is a single, non-repeated disturbance, like a single flick of a rope.

The period of a simple pendulum is given by T = 2π√(L/g). If L becomes 4L, the new period will be 2π√(4L/g) = 2 × (2π√(L/g)) = 2T.

When an object exceeds the speed of sound, it outruns its own sound waves. These wave fronts pile up and form a cone-shaped shock wave, which is heard as a sonic boom when it passes an observer.

The quality of a sound or timbre is what distinguishes a violin from a piano playing the same note (same fundamental frequency). This difference is due to the presence of different overtones (harmonics) at various loudness levels.

This phenomenon describes the spreading out of waves as they encounter a barrier or opening. It is most noticeable when the size of the opening is comparable to the wavelength.

If two points are separated by an integer number of full wavelengths, they are at the exact same point in their respective cycles and are thus in phase.

The term μ represents the inertia of the string. A thicker or denser string (higher μ) will have a slower wave speed for a given tension.

For a pipe closed at one end, the fundamental mode consists of one-quarter of a wavelength fitting inside the pipe (L = λ/4). Therefore, the wavelength is λ = 4L = 4 × 0.25 = 1.0 m.

As the observer moves away, they encounter wave crests less frequently than if they were stationary, resulting in a lower perceived frequency (pitch).

The frequency of a wave is determined by its source and does not change as the wave propagates from one medium to another. The oscillations at the boundary must match on both sides.

The energy from a point source spreads out over the surface of a sphere, whose area is 4πr². Since the total power is constant, the intensity (Power/Area) is inversely proportional to the square of the distance.

For a string fixed at both ends, the number of segments (or antinodes) directly corresponds to the harmonic number. So, 5 segments is the 5th harmonic.

Particles at an antinode reach maximum displacement when particles at a node have zero displacement. Their velocity and displacement are 90 degrees out of phase.

When the driving frequency matches the object's natural frequency of vibration, energy is transferred most efficiently, leading to a large increase in the amplitude of oscillation. This is resonance.

Using the wave equation v = fλ, we can rearrange to find the wavelength: λ = v/f = 340 / 500 = 0.68 m.

When reflecting from a boundary that is free to move (a 'soft' reflection), the wave does not get inverted. It reflects with no change in its phase.

The Wave number (propagation constant), k, is related to the wavelength by k = 2π/λ. It describes the spatial variation of the wave.

In a stationary wave, energy is not propagated. Instead, it oscillates between kinetic energy of the particles and potential energy of the medium, localized within each loop (between nodes).

Sound reaching the stationary cliff is Doppler-shifted because the source moves toward it: f_wall = f * v/(v - u) = 1000 * 330/(330 - 10) = 1031.25 Hz. The cliff (stationary) reflects this frequency unchanged, and the stationary observer receives it with no further shift. Hence the echo ≈ 1031 Hz

For a closed pipe, the harmonics are the odd integers (1st, 3rd, 5th, ...). The fundamental is the 1st harmonic. The first overtone is the 3rd harmonic. The second overtone is the 5th harmonic.

As the particle passes through its equilibrium position, the restoring force is zero, but its kinetic energy and speed are at their maximum.

Since the speed of sound v is proportional to the square root of the absolute temperature T (v ∝ √T), quadrupling T (making it 4T) will change the speed to √4v = 2v.

The beat frequency is f_beat = |f₁ - f₂| = |405 - 400| = 5 Hz. The time period (interval) between beats is the reciprocal of the beat frequency, so T = 1/f_beat = 1/5 = 0.2 s.

For an open pipe, all harmonics are present. The fundamental is f₁ = v/2L = 340/1 = 340 Hz. The third harmonic is f₃ = 3f₁ = 3 × 340 = 1020 Hz.

A full wavelength (λ) corresponds to a full cycle, which is a phase of 2π radians. Therefore, a quarter wavelength (λ/4) corresponds to a quarter of a cycle, which is a phase difference of 2π/4 = π/2 radians (90°).

Distant galaxies are moving away from us. This relative motion causes the light waves to be 'stretched', shifting their frequency towards the red end of the spectrum (lower frequency, longer wavelength).

Waves are a mechanism for transferring energy without a net transfer of the medium itself. The particles of the medium oscillate but return to their equilibrium positions.

For a string, the fundamental is the 1st harmonic. The next frequency is the 2nd harmonic (first overtone). The one after that is the 3rd harmonic (second overtone).

The amplitude is defined as the maximum displacement or distance moved by a point on the wave from its equilibrium position.

The first resonance occurs at approximately L₁ = λ/4 and the second at L₂ = 3λ/4. The difference between them is L₂ - L₁ = 3λ/4 - λ/4 = λ/2. Therefore, λ = 2(L₂ - L₁).

The term ω is the angular frequency, which is related to the frequency f by ω = 2πf. It describes the temporal variation of the wave.

The speed of sound is given by v = √(γP/ρ). If density ρ becomes 4ρ, the new speed will be v' = √(γP/(4ρ)) = (1/√4)v = v/2.

For complete cancellation, the waves must have the same frequency to maintain a constant phase relationship, the same amplitude so the crests and troughs can perfectly cancel, and a phase difference of π (180°) so a crest meets a trough.

All particles within a single loop oscillate together (in phase) with the same frequency, but their amplitude depends on their position, being zero at the nodes and maximum at the antinode.

The refractive index is defined as n = c/v, where c is the speed of light in vacuum and v is the speed in the medium. So, v = c/n = (3×10⁸)/1.5 = 2×10⁸ m/s.

The formula for fundamental frequency is f = (1/2L)√(T/μ). The new frequency f' = (1/2(L/2))√(2T/μ) = (1/L)√(2T/μ) = 2√2 × (1/2L)√(T/μ) = 2√2 f.

Pitch is the perceptual property of sounds that allows their ordering on a frequency-related scale. A high frequency corresponds to a high pitch, and a low frequency corresponds to a low pitch.

The general Doppler formula is f' = f((v ± v_o)/(v ∓ v_s)). Since the observer is moving away from the source, we use (v - v_o) in the numerator. Since the source is moving towards the observer, we use (v - v_s) in the denominator. So, f' = 500((340 - 10)/(340 - 20)) = 500(330/320) = 515.6 Hz.

Radio waves are a type of electromagnetic radiation and can travel through the vacuum of space. They do not require a medium.

The wave number is defined as k = 2π/λ. Since 2π is in radians (dimensionless) and λ is in meters, the unit for k is radians per meter, or simply inverse meters (m⁻¹).

A particle undergoing simple harmonic motion has maximum acceleration at its extreme positions. At a crest, the particle is at its maximum positive displacement, and the acceleration is maximum in the negative (downward) direction.

Wave velocity v = ω/k is constant for a given medium, while maximum particle velocity v_max = ωA depends on the wave's amplitude and frequency. They are two distinct concepts.

Huygens' principle, which states that every point on a wavefront is a source of secondary wavelets, can be used to derive the laws of reflection and refraction, and to explain the phenomenon of diffraction.

The general form is y = A sin(kx - ωt). By comparison, k = 2π and ω = 4π. The wave speed is v = ω/k = (4π)/(2π) = 2 m/s.

Ultrasound refers to sound waves with frequencies higher than the upper audible limit of human hearing, which is typically around 20 kilohertz (20,000 Hz).

As temperature rises, the metal of the tuning fork expands (thermal expansion). This makes the prongs slightly longer and reduces the elasticity, causing it to vibrate more slowly and thus lowering its frequency.

A key characteristic of stationary waves is that there is no net flow of energy along the wave. Energy is localized within the segments between nodes, oscillating between kinetic and potential forms.

The fundamental mode for a wire fixed at both ends has nodes at the two ends and a single antinode in the middle.

Amplitude determines the energy of the wave but is independent of the wave's speed, frequency, or wavelength. You can have a high-frequency wave with a small amplitude, or a low-frequency wave with a large amplitude.

Earthquakes generate primary (P) waves, which are longitudinal, and secondary (S) waves, which are transverse, as well as surface waves.

The total distance traveled by the sound is d = v × t = 340 × 0.1 = 34 m. This is the distance to the insect and back. Therefore, the distance to the insect is half of the total distance, which is 34/2 = 17 m.

Maximum constructive interference occurs when the waves are perfectly in phase. This happens when their phase difference is zero or any integer multiple of 2π (a full cycle).

When a wave goes from a less dense to a more dense medium (like from a light string to a heavy one), it is like hitting a 'hard' boundary. Part of the wave is transmitted, and the reflected part is inverted (phase change of 180°).

Adding mass (the wax) to the prongs of the tuning fork increases their inertia, causing them to oscillate more slowly. This results in a lower frequency of vibration.

As the train approaches, it compresses the sound waves in front of it. The new, shortened wavelength is λ' = (v - v_s)/f = (340 - 20)/200 = 320/200 = 1.6 m. The apparent frequency would be f' = v/λ' = 340/1.6 = 212.5 Hz.

Polarization involves restricting the plane of oscillation. Since the particles in a longitudinal wave oscillate parallel to the direction of propagation, there is only one dimension of oscillation to begin with, and thus it cannot be restricted further. Polarization is a property exclusive to transverse waves.

In large halls, sound waves reflecting off different surfaces can meet at certain points out of phase, leading to destructive interference and creating areas where the sound is significantly quieter or 'dead'.

The formula for the period is T = 2π√(L/g). Since g becomes g/6, the new period T' = 2π√(L/(g/6)) = √6(2π√(L/g)) = √6 T.

This is the fundamental purpose of all mechanical waves: to transfer energy without transferring matter. Even electromagnetic waves transfer energy.

The intensity (power per unit area) of a wave is proportional to the square of its amplitude. It is also proportional to the square of its frequency.

For a closed pipe, f_c = v/4L. For an open pipe, f_o = v/2L. The ratio f_c : f_o is (v/4L) : (v/2L), which simplifies to 1/4 : 1/2, or 1:2.

When a vibrating body is brought into contact with another, it can force the second body to vibrate. This is the general phenomenon.

When the source and observer are moving towards each other, the relative speed is at its maximum, leading to the largest possible increase in frequency (highest pitch).

A node is a point of zero displacement and an antinode is a point of maximum displacement. The distance between them is a quarter of a full wavelength.

Diffraction effects are most significant when the size of the obstacle or opening is on the order of the wavelength of the waves.

Frequency is proportional to the square root of tension (f ∝ √T). If tension increases by 21%, it becomes 1.21T. The new frequency will be proportional to √(1.21T) = 1.1√T. This is a 10% increase.

By comparing the equation with the standard form y = A sin(ωt - kx), we see that the wave number k = 2π. Since k = 2π/λ, we have 2π = 2π/λ, which gives λ = 1 m.

This is the defining condition for beats. The slight difference causes the phase relationship to cycle between constructive and destructive interference, producing the periodic change in loudness.

Particles of water on the surface move in a roughly circular or elliptical path, which has both a vertical (transverse) and a horizontal (longitudinal) component of motion.