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VICPhysicsQuick questions
Unit 4: How have new ideas and ways of thinking developed our understanding of the physical world?
Quick questions on Polarisation and Malus's law: VCE Physics Unit 4
7short 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 procedure?Show answer
1. First polariser, unpolarised input. $I_1 = I_0 / 2$. 2. Second polariser, polarised input. $I_2 = I_1 \cos^2(\theta_{12})$ where $\theta_{12}$ is the angle between the first and second polarisers' axes.
What is worked example. Three polarisers?Show answer
Unpolarised light of intensity $I_0$ passes through three polarisers oriented at $0^\circ$, $45^\circ$ and $90^\circ$.
What is applying Malus's law to unpolarised input?Show answer
Malus's law requires polarised input. For unpolarised input use the half-rule.
What is cumulative angle instead of adjacent angle?Show answer
The angle in Malus's law is between consecutive polarisers, not from some absolute reference.
What is forgetting to square the cosine?Show answer
$I = I_0 \cos(\theta)$ is wrong. The intensity depends on the square of the amplitude, so $\cos^2$.
What is cross polarisers thought to give half intensity?Show answer
With $\theta = 90^\circ$, $\cos^2 = 0$. Crossed polarisers transmit zero intensity.
What is mixing radians and degrees?Show answer
$\cos^2(60^\circ) = 1/4$, not $\cos^2(60$ radians$) \approx 0.86$. Use the correct angle unit.
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