Measurement of a Thermal Expansion Coefficient for a Metal by Diffraction Patterns from a Narrow Slit

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In this work, we made an effort to determine linear coefficient of thermal expansion of metal using single-slit diffraction. An aluminium strip was used as sample. The design of the apparatus for this method allows for the width of a single slit to increase by the same amount as the thermal expansion of a length of a strip or a rod of a material. The increase in the slit width, hence the linear expansion, can be determined by measuring the fringe width. A He-Ne laser with a wavelength of 632.8 nm was used to obtain a diffraction pattern for the single slit. The value of the linear coefficient of thermal expansion of the material can then be calculated using the principle knowledge of diffraction equation and thermal expansion. The experimental result was found that the linear coefficient of thermal expansion of aluminium is 22.512 × 10^-6 (C°)^-1, giving a 2.545 % error.