The table below shows measurements from a jewellery workshop. A jeweller shines a narrow light beam into three polished stones to compare the number of brig...
Question 1 Report
The table below shows measurements from a jewellery workshop. A jeweller shines a narrow light beam into three polished stones to compare the number of bright internal flashes seen from above. Each stone has the same cut and is surrounded by air. The critical angle is measured for light travelling from the stone to air. The flashes are caused by rays reflecting inside the stone before they emerge. The jeweller uses the information when choosing a material for a decorative pendant.
| Stone | Critical angle / degrees | Bright flashes counted |
|---|---|---|
| quartz | 40 | 5 |
| zircon | 33 | 9 |
| synthetic spinel | 36 | 7 |
(a) Which stone produces the most bright flashes? [1]
(b) What relationship is suggested between critical angle and number of flashes? [1]
(c) Which process produces the flashes inside a stone? [1]
(d) When a ray strikes inside zircon at 35 degrees, what happens? [1]
(e) What is the difference between the critical angles of quartz and zircon? [1]
(f) Which stone would be chosen for the brightest design using this evidence? [1]
Answer Details
(a) Zircon produces the most bright flashes, with 9 flashes. [1]
(b) The results suggest that a lower critical angle gives more flashes. A lower critical angle means more rays meet an internal surface above the critical angle and so undergo total internal reflection. [1]
(c) The flashes are produced by total internal reflection. [1]
(d) In zircon, \(35^\circ\) is greater than its critical angle of \(33^\circ\), so total internal reflection occurs. [1]
(e) \[40^\circ-33^\circ=7^\circ\] The difference is \(7^\circ\). [1]
(f) The evidence supports choosing zircon, because it gives the highest number of bright flashes. [1]
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