Physics - Heat & Thermo Question with Solution | TestHub
By varying the voltage applied to the kettle, you can change its power consumption P. Depending on P, the kettle with water can be heated to different maximum temperatures. This dependence is shown in Table 1.
Table 1
Power P (W) | 0 | 100 | 200 | 300 |
|---|---|---|---|---|
Temperature T (°C) | 20 | 40 | 60 | 80 |
Table 2 shows the variation of temperature with time when the kettle with a 300 W heater is switched off. The heat capacity of the empty kettle C₀ = 100 J/K; specific heat of water = 4200 J/(kg K); density of water = 1000 kg/m³. Assume Newton’s law of cooling.
Table 2
Time t (s) | 0 | 60 | 300 | 600 | 1200 | 2400 |
|---|---|---|---|---|---|---|
Temperature T (°C) | 80 | 75 | 60 | 45 | 30 | 20 |
The rate of heat loss at after the heater is switched off (as in table-2) is.
Options:
Answer:
Solution:
The steady 100 W heater gives a kettle temperature of 40°C in the first table.
After the heater is switched off, the second table gives 45°C at 600 s.
Answer B.
