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Physics: Waves & Optics Flashcards

7 cards from real AP practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. A wave on a string has a frequency of 4 Hz and a wavelength of 0.5 m. What is the wave speed?

    Answer: 2 m/s

    Wave speed v = fλ = 4 Hz × 0.5 m = 2 m/s.

  2. Which phenomenon explains why a straw appears bent when placed in a glass of water?

    Answer: Refraction

    Refraction occurs when light changes speed at the water-air interface, bending the apparent position of the straw.

  3. Two identical waves traveling in opposite directions on a string create a standing wave. The distance between two adjacent nodes is 0.3 m. What is the wavelength of the original traveling waves?

    Answer: 0.6 m

    Adjacent nodes are separated by λ/2, so λ = 2 × 0.3 m = 0.6 m.

  4. A sound source emitting 500 Hz moves toward a stationary observer at 34 m/s. If the speed of sound is 340 m/s, what frequency does the observer hear?

    Answer: 550 Hz

    Using the Doppler formula f' = f(v/(v−vs)) = 500(340/306) ≈ 556 Hz, closest to 550 Hz.

  5. In a double-slit experiment, the slit separation is doubled while keeping all other variables constant. What happens to the fringe spacing?

    Answer: It is halved

    Fringe spacing Δy = λL/d; doubling d halves the fringe spacing.

  6. A light ray travels from glass (n = 1.5) into air (n = 1.0). What is the critical angle for total internal reflection?

    Answer: 41.8°

    sin θc = n2/n1 = 1.0/1.5 = 0.667, so θc = arcsin(0.667) ≈ 41.8°.

  7. Which type of wave requires a material medium to propagate?

    Answer: Mechanical waves

    Mechanical waves (e.g., sound, water waves) require a medium, unlike electromagnetic waves.