Waves and optics flashcards

Waves and optics covers the fundamental properties of waves, including amplitude, frequency, wavelength, period and wave speed, linked by v = f x wavelength. Students must distinguish between transverse and longitudinal waves and understand polarisation as evidence for transverse waves. Superposition leads to interference and diffraction, explained using path difference and the double-slit equation. Stationary waves arise from two identical waves travelling in opposite directions, producing nodes and antinodes. Refraction is explained by the change in wave speed at a boundary, described by Snell's law. Total internal reflection occurs beyond the critical angle and has practical applications in optical fibres. The wave nature of light is demonstrated by diffraction grating experiments, and students should be able to use the grating equation d sin theta = n x wavelength confidently.

1. Card 1

   What is the relationship between wave speed, frequency and wavelength?

   Wave speed equals frequency multiplied by wavelength: v = f x wavelength. Speed is in m/s, frequency in Hz and wavelength in metres.

2. Card 2

   How do transverse and longitudinal waves differ?

   In transverse waves oscillations are perpendicular to the direction of energy transfer; in longitudinal waves oscillations are parallel to it.

3. Card 3

   What is polarisation and what does it tell us about waves?

   Polarisation restricts oscillations to one plane. Only transverse waves can be polarised, confirming that light is a transverse wave.

4. Card 4

   State the principle of superposition.

   When two waves meet, the resultant displacement equals the vector sum of their individual displacements at every point.

5. Card 5

   What conditions are needed for a stable interference pattern?

   The two sources must be coherent, meaning they have a constant phase difference and the same frequency.

6. Card 6

   What is path difference and how does it determine constructive or destructive interference?

   Path difference is the extra distance one wave travels. Constructive interference occurs at whole-number wavelength differences; destructive at half-number differences.

7. Card 7

   State the double-slit equation for fringe spacing.

   Fringe spacing w = lambda x D / s, where lambda is wavelength, D is slit-to-screen distance and s is the slit separation.

8. Card 8

   How is a stationary wave formed?

   A stationary wave forms when two identical waves of the same frequency and amplitude travel in opposite directions and superpose.

9. Card 9

   What are nodes and antinodes in a stationary wave?

   Nodes are points of zero amplitude where destructive interference is permanent; antinodes are points of maximum amplitude.

10. Card 10

    State Snell's law of refraction.

    n1 sin theta1 = n2 sin theta2, where n is the refractive index of each medium and theta is the angle to the normal.

11. Card 11

    What is total internal reflection and when does it occur?

    Total internal reflection occurs when light travels from a denser to a less dense medium and the angle of incidence exceeds the critical angle.

12. Card 12

    State the diffraction grating equation.

    d sin theta = n x lambda, where d is the grating spacing, n is the order and lambda is the wavelength of light used.

• Students often confuse the wavelength of a stationary wave with the distance between adjacent nodes, forgetting that one full wavelength spans two node-to-node gaps.
• A common error is applying total internal reflection to light travelling from a less dense medium into a denser one, when it can only occur going from denser to less dense.
• Many students incorrectly assume that diffraction only occurs with light, when in fact all waves diffract and the effect is greatest when the gap size is similar to the wavelength.

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