A manufacturer tests four samples for use as the insulating layer in an oven glove.
Each sample has the same area and is placed between a hot metal plate and the same temperature sensor. The metal plate is kept at 80 ∘C80\ ^\circ\text{C}80 ∘C and the sensor starts at 20 ∘C20\ ^\circ\text{C}20 ∘C. Each test lasts 30 s.
The table shows the results.
| Sample | Material | Thickness in mm\text{mm}mm | Thermal conductivity in W/m K\text{W/m K}W/m K | Temperature rise of sensor in ∘C^\circ\text{C}∘C |
|---|---|---|---|---|
| P | felt | 4 | 0.04 | 9 |
| Q | silicone rubber | 4 | 0.20 | 19 |
| R | silicone rubber | 8 | 0.20 | 12 |
| S | felt | 8 | 0.04 | 5 |
Give the letter of the sample that transfers the least energy to the sensor during the test.
Samples P and Q have the same thickness.
Describe what their results show about the effect of thermal conductivity on the rate of energy transfer.
Samples Q and R are made from the same material, but sample R is thicker.
State the effect of the greater thickness on the rate of energy transfer to the sensor.