Physics - Heat & Thermo Question with Solution | TestHub
An engineer is instructed to design a tank to measure the heat capacity of liquids. The tank has insulating walls of negligible heat capacity, a hole in the bottom with a drain plug fitted with a light rod, and ten electric immersion heaters each rated 5 kW. Water is filled in the tank at 20°C and the heaters are switched on. After 15 hours the water starts boiling at normal atmospheric pressure. The water is drained and the tank is filled with oil of specific gravity 0.7. The oil takes 3.15 hours to heat from 20°C to 60°C at normal atmospheric pressure.
It is suggested that the air in the tank above the oil can be pressurized at 4 atm above normal air pressure, which of the following is INCORRECT if pressure is increased to the suggested value.
Options:
Answer:
Solution:
For the same oil mass, heater power and temperature rise from 20°C to 60°C, the heating time is set by the heat needed and the heater power.
Increasing the gas pressure above the oil does not greatly change this heat requirement. Thus A is the incorrect statement.
Higher pressure presses the drain plug harder, increasing the force needed to lift it (B).
Once opened, the greater pressure difference drives faster outflow (C), reducing drain time (D).
