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A lamp is switched on and viewed through two polarising filters P and Q, as shown - Edexcel - A-Level Physics - Question 5 - 2023 - Paper 2
Question 5
A lamp is switched on and viewed through two polarising filters P and Q, as shown. The lamp appears dark when viewed through P and Q. Q is rotated through 180°. Whic... show full transcript
Worked Solution & Example Answer:A lamp is switched on and viewed through two polarising filters P and Q, as shown - Edexcel - A-Level Physics - Question 5 - 2023 - Paper 2
Step 1
Which row gives the appearance of the lamp after Q has rotated by 90°?
Answer
When Q is rotated by 90°, it will be oriented at an angle to P. Since polarising filters only allow light aligned with their polarization direction to pass through, the lamp will appear bright at this angle. Therefore, the answer for the first rotation is 'bright'.
Step 2
Which row gives the appearance of the lamp after Q has rotated by 180°?
Answer
After rotating Q by 180°, it will become parallel to its original position but with the opposite polarization direction. This means it will now block light passing through filter P, which means the lamp will appear dark. Therefore, the answer for the second rotation is 'dark'.