A LevelPhysicsCambridge (CIE)Flashcards7. WavesProgressive Waves

Progressive Waves (Cambridge (CIE) A Level Physics): Flashcards

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  • FrontProgressive Waves

    Define progressive wave.

Cards in this collection (26)

  • Define progressive wave.

    A progressive wave transfers energy (without transferring matter) through a medium or a vacuum, as particles oscillate about fixed positions.

  • In a wave, oscillations can be perpendicular or parallel to the direction of wave travel. What is the difference between a transverse wave and a longitudinal wave?

    • In a transverse wave, oscillations are perpendicular to the direction of wave travel

    • In a longitudinal wave, oscillations are parallel to the direction of wave travel

  • What three wave effects can be demonstrated using a ripple tank?

    • Reflection

    • Refraction

    • Diffraction

  • Define amplitude.

    Amplitude is the maximum displacement of a particle in a wave from its equilibrium position.

  • Define wavelength.

    Wavelength is the distance between points on successive oscillations of a wave that are in phase.

  • Frequency is the number of complete oscillations per .........., measured in hertz (Hz).

    Frequency is the number of complete oscillations per unit time, measured in hertz (Hz).

  • What is the phase difference, in degrees, between two waves that are in antiphase?

    180° (π radians).

  • True or False?

    Progressive waves transfer matter as well as energy.

    False.

    Progressive waves transfer energy without transferring matter — particles simply oscillate back and forth about fixed positions.

  • Define time-base (of a cathode-ray oscilloscope).

    Time-base is how many seconds each division on the screen represents, measured in s div-1 or s cm-1.

  • How is a d.c. voltage displayed on a cathode-ray oscilloscope screen?

    As a horizontal line at the relevant voltage.

  • What do the x-axis and y-axis of a cathode-ray oscilloscope display represent?

    • x-axis: time

    • y-axis: voltage (y-gain)

  • Describe how to determine the frequency of a wave from a cathode-ray oscilloscope trace.

    • Count the number of wavelengths shown on the screen

    • Multiply the number of divisions by the time-base to find the total time

    • Divide the total time by the number of wavelengths to find the period, T

    • Calculate frequency using f = \frac{1}{T}

  • An a.c. current displayed on an oscilloscope is represented as a .......... wave.

    An a.c. current displayed on an oscilloscope is represented as a transverse wave.

  • True or False?

    The time-base of an oscilloscope is measured in volts per division.

    False.

    The time-base is measured in seconds per division (e.g. s div-1) — it controls the time represented by each horizontal division, not the voltage.

  • State the wave equation, defining each symbol.

    v = f \lambda

    • v is wave speed in m s-1

    • f is frequency in Hz

    • λ is wavelength in m

  • The derivation of v = fλ starts from the definition of speed. What equation for speed is used as the starting point?

    \text{speed} = \frac{\text{distance}}{\text{time}}

  • True or False?

    The wave equation v = fλ only applies to transverse waves.

    False.

    The wave equation applies to both transverse and longitudinal waves.

  • At constant wave speed, how are frequency and wavelength related?

    They are inversely proportional — as wavelength increases, frequency decreases, and vice versa.

  • The wave equation is sometimes written as c = fλ, but c should only be used for .........., since it usually represents the speed of light.

    The wave equation is sometimes written as c = fλ, but c should only be used for electromagnetic waves, since it usually represents the speed of light.

  • Define intensity of a wave.

    Intensity is the power per unit area carried by a wave, measured perpendicular to the direction of travel: I = \frac{P}{A}

  • How does the intensity of a wave depend on its amplitude?

    Intensity is proportional to amplitude squared: I \propto A^{2}

  • How does the intensity of a wave depend on its frequency?

    Intensity is proportional to frequency squared: I \propto f^{2}

  • Define a spherical wave.

    A spherical wave is a wave from a point source which spreads out equally in all directions.

  • The area a spherical wave passes through at distance r from the source is the surface area of a sphere, ...........

    The area a spherical wave passes through at distance r from the source is the surface area of a sphere, 4πr2.

  • If the distance from a point source is doubled, by what factor does the wave intensity decrease (assuming no energy is absorbed)?

    By a factor of 4, since I \propto \frac{1}{r^{2}}

  • True or False?

    The intensity of a wave decreases linearly with increasing distance from the source.

    False.

    Intensity follows an inverse square law with distance, so it decreases much more rapidly than linearly: I \propto \frac{1}{r^{2}}

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