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Unit 2 Electricity and Light

Quick questions on Wave properties: interference, diffraction and the grating - WJEC A-Level Physics

4short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.

What is diffraction?
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Diffraction is the spreading of waves as they pass through a gap or around an obstacle. The spreading is greatest when the gap width is comparable to the wavelength, which is why sound (long wavelength) diffracts round a doorway but light (very short wavelength) barely does.
What is the diffraction grating?
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A diffraction grating has many equally spaced slits a distance dd apart. Sharp bright maxima appear at angles where dsin⁡θ=nλd\sin\theta = n\lambda, with nn the order. Measuring the angle of a known order lets you find the wavelength precisely, a specified practical.
What is q1?
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Light of wavelength 600 nm600\,\text{nm} hits a grating with 300 000300\,000 lines per metre. Find the angle of the first-order maximum. [3 marks]
What is q2?
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State the path-difference condition for constructive interference. [1 mark]

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