Waves flashcards

Waves transfer energy from one place to another without transferring matter. Students must understand the difference between transverse and longitudinal waves, and be able to define and calculate wave properties including frequency, wavelength, amplitude and wave speed using the wave equation. The electromagnetic spectrum must be known in order, along with the properties and uses of each type of radiation. Students should also understand reflection, refraction and sound as a longitudinal wave, including how sound travels through different media. The behaviour of waves at boundaries, the concept of wavefronts, and the relationship between wave speed, frequency and wavelength are all essential. Understanding how waves are used in real-world applications such as communication, medical imaging and cooking rounds off this topic.

1. Card 1

   What is the difference between a transverse and a longitudinal wave?

   In a transverse wave the oscillations are perpendicular to the direction of travel. In a longitudinal wave the oscillations are parallel to the direction of travel.

2. Card 2

   State the wave equation and define each term.

   wave speed (m/s) = frequency (Hz) x wavelength (m), written as v = f x lambda. Frequency is oscillations per second; wavelength is the distance between two identical adjacent points.

3. Card 3

   What is the amplitude of a wave?

   Amplitude is the maximum displacement of a point on the wave from its undisturbed (equilibrium) position. A larger amplitude means more energy is being transferred by the wave.

4. Card 4

   What is the frequency of a wave and what unit is it measured in?

   Frequency is the number of complete wave cycles passing a point per second. It is measured in hertz (Hz). A frequency of 1 Hz means one complete wave per second.

5. Card 5

   List the electromagnetic spectrum in order of increasing frequency.

   Radio, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays. As frequency increases, wavelength decreases and the radiation carries more energy per photon.

6. Card 6

   What happens to a wave when it crosses a boundary between two different media?

   The wave undergoes refraction: its speed changes. If it enters a denser medium it slows down and bends towards the normal; if it enters a less dense medium it speeds up and bends away.

7. Card 7

   How does sound travel and why can it not travel through a vacuum?

   Sound is a longitudinal wave that travels as compressions and rarefactions through a medium. It needs particles to vibrate, so it cannot travel through a vacuum where there are no particles.

8. Card 8

   What is the relationship between wave speed and the medium it travels through?

   Wave speed depends on the medium. Sound travels faster in solids than liquids than gases. All electromagnetic waves travel at the same speed (3 x 10^8 m/s) in a vacuum.

9. Card 9

   State the law of reflection.

   The angle of incidence equals the angle of reflection, both measured from the normal to the surface at the point where the wave meets the boundary.

10. Card 10

    What is the period of a wave and how is it related to frequency?

    The period (T) is the time taken for one complete wave cycle, measured in seconds. It is the reciprocal of frequency: T = 1 / f. A higher frequency means a shorter period.

11. Card 11

    Give one use and one hazard for ultraviolet radiation.

    Ultraviolet is used in fluorescent lamps and to detect forged banknotes. It is hazardous because it can cause skin cancer and damage eyesight with prolonged exposure.

12. Card 12

    Why does a wave change direction when it refracts?

    Refraction occurs because the wave speed changes at the boundary. The change in speed causes the wavefronts to bend, changing the direction of travel unless the wave hits the boundary at normal incidence.

• Many students confuse amplitude with wavelength, incorrectly stating that amplitude is the distance from one wave peak to the next rather than the displacement from the equilibrium position.
• A common error is thinking that a higher wave speed always means a higher frequency, when in fact frequency is determined by the source and does not change when a wave moves between media.
• Students often forget that all electromagnetic waves travel at the same speed in a vacuum and incorrectly suggest that gamma rays travel faster than radio waves because they have higher frequency.

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