Polarisation & Malus’ Law Challenge
25 NEET-standard questions on polarised and unpolarised waves, polaroids and the pass-axis, Malus’ law, crossed polaroids and a third polaroid in between. Answer each one. If you get it wrong, Vidya Ma’am explains it with an animated movie you can control, a slider to play with, and a step-by-step solution. Then try again.
NCERT Physics XII Part II · Ch. 10 · pp. 269–272Keys: A–D or 1–4 to answer
🧠 Formula memory tricks (open before you start)
Unpolarised → polaroidI = I₀/2Rotating one polaroid changes nothing
Malus’ lawI = I₀cos²θField: E cos θ. Only for light already polarised
The cos² ladder0°→1 · 30°→3/4 · 60°→1/4 · 90°→0θ is the angle between pass-axes
Crossed polaroidsθ = 90° → I = 0Parallel (0°) passes everything
Third polaroid between crossedI = (I₀/4) sin²2θMaximum at 45°: I₀/4. From unpolarised: I/8
Full turnTwo maxima and two minima in 2πcos²θ has period 180°
Longitudinal wavesCannot be polarisedPolarisation is special to transverse waves
Brewster (beyond NCERT)tan iB = nReflected ⟂ refracted: i + r = 90°
right first tryfixed after explanationstill to fix
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