This question tests understanding of wave behavior at boundaries between different media, specifically how wavelength changes when wave speed changes. When a wave crosses from one medium to another, frequency remains constant (determined by the source), but wave speed changes based on medium properties. Using v = fλ, when the wave enters fat tissue where v decreases from 1540 m/s to 1450 m/s while f remains at 2.0 MHz, the wavelength λ must decrease proportionally to maintain the relationship. This is a fundamental principle in wave propagation: frequency is conserved across boundaries, but wavelength adjusts to accommodate the new wave speed. The common misconception is thinking frequency changes at boundaries, but frequency is set by the source and remains constant. For verification, always check that v = fλ holds in each medium with the same frequency.

This question tests understanding of how wavelength measurements reveal wave speed differences. Using v = fλ with constant frequency f, the wave speeds are v₁ = f × 1.2 mm and v₂ = f × 0.8 mm. Since λ₂ < λ₁, it follows that v₂ < v₁, meaning the wave speed is lower in Fluid 2. The ratio v₂/v₁ = λ₂/λ₁ = 0.8/1.2 = 2/3, confirming that Fluid 2 has a lower wave speed. This makes physical sense as fluids with different densities or elastic properties support different wave speeds. The key principle is that when frequency is held constant by the source, wavelength directly indicates wave speed: shorter wavelength means slower wave speed. To verify such problems, use the wave equation v = fλ and recognize that wavelength and wave speed are proportional at constant frequency.

This question tests understanding of the relationship between wave speed, frequency, and wavelength when the medium changes. The tuning fork produces a fixed frequency f regardless of the surrounding medium. In the helium-rich environment where sound speed is higher than in air, the wave equation v = fλ requires that wavelength λ must increase proportionally to maintain the constant frequency. This is because wavelength λ = v/f, so when v increases and f remains constant, λ must increase. The common misconception is thinking that the medium affects the source frequency, but a tuning fork's vibration frequency is determined by its physical properties, not the surrounding medium. To verify such problems, identify what remains constant (source frequency) and apply v = fλ to determine how other quantities must change.

This question tests understanding of the Doppler effect for reflected waves. When a source and observer move toward each other, the observed frequency increases because the relative motion compresses the effective wavelength between successive wavefronts. In Doppler ultrasound, blood cells act as moving reflectors: they first receive a higher frequency as they approach the transducer (first Doppler shift), then reflect this higher frequency back while still moving toward the transducer (second Doppler shift). This double Doppler shift results in a measured frequency higher than the emitted frequency. The wave speed in the medium remains constant; only the apparent frequency changes due to relative motion. The key principle is that approaching motion decreases the time between wavefront arrivals, increasing the observed frequency. For Doppler problems, remember that frequency increases for approach and decreases for recession.

This question tests understanding of wave speed dependence on medium properties, specifically the relationship between tension and wave speed in a string-like medium. For waves on a string, the wave speed is given by v = √(T/μ), where T is tension and μ is linear mass density. Since μ remains constant and tension T increases, the wave speed v must increase. The fundamental wave equation v = fλ shows that when frequency f is fixed (set by the external driver) and wave speed v increases, wavelength λ must also increase proportionally. The key insight is recognizing that frequency is determined by the source (loudspeaker), not the medium properties. To verify such problems, check that the wave equation v = fλ is satisfied and remember that frequency is set by the source while wave speed depends on medium properties.

This question tests understanding of how wave properties change when wave speed increases in a medium while the source frequency remains constant. The key principle is that for transverse waves on strings or fibers, increasing tension increases wave speed, and with unchanged source frequency, wavelength must increase according to λ = v/f. When fiber tension increases, wave speed v increases, but the tap maintains the same temporal pattern (frequency content). Therefore, wavelength must increase proportionally to maintain v = fλ, making answer A correct. Choice B incorrectly inverts the wavelength relationship, while C wrongly suggests frequency changes when only the medium properties change. For mechanical waves, remember that the source sets the frequency while the medium determines the wave speed, and wavelength adjusts accordingly.

This question tests understanding of the wave equation v = fλ when wave speed changes. With fixed source frequency (500 Hz) and higher wave speed in helium, wavelength must increase to maintain the relationship λ = v/f. Since v increases while f remains constant, λ must increase proportionally. The correct answer A correctly applies this relationship to predict longer wavelength in helium. Answer B incorrectly claims frequency changes, violating the principle that source determines frequency. When waves enter different media, always remember: frequency stays constant (set by source), wavelength adjusts to match the new wave speed.

This question tests understanding of wave amplitude versus frequency in absorption phenomena. When light passes through tissue with varying blood content, absorption changes affect the transmitted intensity (amplitude) but not the frequency of the electromagnetic wave. The LED source sets a fixed frequency that doesn't change during propagation. The correct answer B accurately describes intensity decrease from increased attenuation while frequency remains fixed. Answer A incorrectly suggests frequency changes, which would violate energy conservation for electromagnetic waves. For absorption problems, distinguish between amplitude effects (intensity, attenuation) and frequency effects (color, energy per photon).

This question tests understanding of temperature effects on sound waves. When air temperature increases, sound speed increases (v ∝ √T for ideal gases), but the source frequency remains fixed at 2.0 kHz. Using λ = v/f, wavelength must increase when v increases and f stays constant. The correct answer A correctly predicts wavelength increase from the speed increase. Answer B incorrectly suggests frequency changes with temperature - frequency is set by the source, not the medium. For temperature-dependent wave problems, remember that only wave speed changes with temperature while source frequency remains constant.

This question tests understanding of wave speed determination in strings. Wave speed on a string depends only on medium properties (v = √(T/μ)), not on how we drive it. Changing driving frequency doesn't change the rope's tension or mass density, so wave speed remains constant. By v = fλ, if v is constant and f increases, then λ must decrease proportionally. The correct answer B correctly states that wave speed is unchanged and increasing frequency decreases wavelength. Answer A incorrectly claims frequency affects wave speed, confusing cause and effect. For wave propagation problems, remember: medium properties determine speed, source determines frequency, and wavelength adjusts to satisfy v = fλ.