(455) HL Single slit diffraction [IB Physics HL]

Single Slit Diffraction

Overview

  • Diffraction: Spreading of waves when light passes through a small opening (slit) comparable to the wavelength of light.

  • Involves understanding how light behaves as a wave.

Setup

  • Slit Opening (B): The width of the slit through which light passes.

  • Screen (Distance R): The distance from the slit to the screen where the light is projected.

  • Expectation: If light were just particles, intensity would be brightest directly behind the slit.

Diffraction Pattern

  • When slit opening (B) is similar to the wavelength of light, diffraction occurs, leading to:

    • Central Maximum: Brightest part located directly behind the slit.

    • Secondary Maxima: Weaker peaks to the sides of the central maximum.

  • Angles (θ): Defined for measuring the positions of the maxima and minima on the screen.

Intensity Distribution

  • Intensity or brightness of light can be plotted:

    • X-axis: angle in radians.

    • Y-axis: intensity of light.

  • Equation for First Minimum: θ = λ / B, where λ is wavelength and B is slit width.

  • Central Maximum Width: Approximately twice the angle found for the first minimum.

Real-World Example

  • Parameters:

    • Distance (R) = 3.5 m

    • Wavelength (λ) = 633 nm (or 633 x 10^-9 m)

    • Slit Width (B) = 0.59 cm (or 0.59 x 10^-2 m)

Calculations

  1. Calculate θ:

    • θ = λ / B = (633 x 10^-9 m) / (0.59 x 10^-2 m) = 1.07 x 10^-4 radians.

  2. Find Real Distance (L):

    • L = Rθ = 3.5 m * (1.07 x 10^-4) = 3.75 x 10^-4 m.

  3. Width of Central Maximum:

    • Width = 2 * L = 2 * (3.75 x 10^-4 m) = 7.5 x 10^-4 m (or 0.75 mm).

Conclusion

  • The calculations demonstrate how to determine the diffraction pattern and measurements of the central maximum width using practical values.