Introduction

Thomas Young’s double slit experiment forms a key piece in the acceptance of the wave model of light as highlighted in the Physics study design but what is the evidence? In this program we will use experimental data from water waves to show the basis of Young’s premise for predicting the behaviour of waves and then apply this to investigation how diffraction and interference of light can be applied to predict fringe patterns or calculate wavelengths.

Program Overview

In this program students will use ripple tanks to investigate the diffraction of water waves through gaps and around objects and compare to predictions. They will investigate and analyse interference of waves in water from two sources as a means to confirm the outcome used by Young to predict the behaviour of light through slots. They will then experimentally reproduce Young’s double slit experiment and interpret the results, using data to calculate the wavelengths of various sources of light and confirm the wave-like behaviour of light.

As an extension activity students will investigate the diffraction of light around objects and investigate the limits of resolution available with light.

This program offers various starting off points for student experimental investigations.

Curriculum Focus

Unit 4 Area of Study 1 – How has understanding about the physical world changed?

Light as a wave

• describe light as a transverse electromagnetic
• investigate and explain theoretically and practically diffraction as the directional spread of various frequencies with reference to different gap width or obstacle size, including the qualitative effect of changing the  ratio, and apply this to limitations of imaging using electromagnetic waves
• explain the results of Young’s double slit experiment with reference to:
• evidence for the wave-like nature of light
• constructive and destructive interference of coherent waves in terms of path differences: nλ and respectively, where n = 0,1, 2,…
• effect of wavelength, distance of screen and slit separation on interference patterns: when L>>d

Unit 4 Area of Study 2 – How is scientific inquiry used to investigate fields, motion or light?

Investigation design

• explain the characteristics of the selected scientific methodology and method including:
  • techniques of primary qualitative and quantitative data generation.
  • appropriateness of the use of independent, dependent and controlled variables
• identification of, and distinction between, error and uncertainty
• identify and apply health, safety and ethical guidelines relevant to the selected investigation

Scientific evidence

• apply methods of organising, analysing and evaluating primary data to identify patterns and relationships including:
  • the physical significance of the gradient of linearised data;
  • causes of uncertainty