A student investigates refraction using a rectangular plastic block.
She wants to find the refractive index of the plastic. She shines light rays into the block at different angles of incidence and measures the resulting angles of refraction.
Her data is shown in the table below:
| Angle of incidence, iii | Angle of refraction, rrr | sini\sin isini | sinr\sin rsinr |
|---|---|---|---|
| 0∘0^\circ0∘ | 0∘0^\circ0∘ | 0.00 | 0.00 |
| 20∘20^\circ20∘ | 14∘14^\circ14∘ | 0.34 | 0.24 |
| 30∘30^\circ30∘ | 21∘21^\circ21∘ | 0.50 | [A] |
| 40∘40^\circ40∘ | 27∘27^\circ27∘ | 0.64 | [B] |
| 50∘50^\circ50∘ | 33∘33^\circ33∘ | 0.77 | 0.54 |
Calculate the missing values [A] and [B] of sinr \sin r\,sinr from the table, giving your answers to 2 decimal places.
The student plots a graph of sini \sin i\,sini on the yyy-axis against sinr \sin r\,sinr on the xxx-axis. The straight line of best fit passes through the origin (0.00,0.00)(0.00, 0.00)(0.00,0.00) and the coordinate point (0.50,0.71)(0.50, 0.71)(0.50,0.71). Use these values to find the refractive index of this plastic block.
Suggest two reasons why using a graph to find the refractive index is a better method than simply calculating it using a single pair of angles from the table.