A student investigates how insulation thickness affects cooling. The table shows possible tests using identical containers and the same insulating material.
| Test | Insulation thickness in mm\mathrm{mm}mm | Initial water temperature in ∘C^\circ\mathrm{C}∘C | Water volume in cm3\mathrm{cm^3}cm3 |
|---|---|---|---|
| P | 10 | 80 | 100 |
| Q | 20 | 80 | 100 |
| R | 20 | 60 | 100 |
| S | 10 | 80 | 200 |
The room temperature and cooling time are the same in all tests.
Which pair allows a valid comparison of insulation thickness?
tests P and Q
tests P and R
tests Q and R
tests P and S