Quantrex Quantrex AcademyJEE · NEET · NDA PYQs with solutions Open app
Concepts Of Physics MCQ Edition [Volume 2]PhysicsHeat Transfer

A metal block having a heat capacity of 80 J ^ C ⁻¹ is located in a room at 20^ C and is heated electrically. Once the temperature attains 30^ C , the heater is turned off. Just after the heater is turned on, the block's temperature increases at a rate of 2^ C s ⁻¹ , and just after it is turned off, the temperature decreases at a rate of 0.2^ C s ⁻¹ . Assuming Newton's law of cooling is valid, determine the power rad

Options

  1. A8 W
  2. B4 W
  3. C16 W
  4. D12 W

Correct answer

A. 8 W

Step-by-step solution

According to Newton's law of cooling, the rate of heat loss to the surroundings is proportional to the temperature difference between the body and the surroundings. dQ dt = k(T - T₀) Given that the heat capacity of the block is C = 80 J ^ C ⁻¹ and the room temperature is T₀ = 20^ C . Just after the heater is turned off at T = 30^ C , the rate of cooling is 0.2^ C s ⁻¹ . The rate of heat loss at this instant is: dQ dt = C (- dT dt ) = 80 0.2 = 16 W Substituting these values into Newton's law of cooling: 16 = k(30 -

Practice Heat Transfer on Quantrex Academy →

More from Heat Transfer

A liquid-nitrogen container is constructed from a 1 -cm thick styrofoam sheet with a thermal conductivity of 0.025 J s ⁻¹ m ⁻¹ ^ C ⁻¹ . Liquid nitrogen at 80 K is stored inside. A A uniform slab measuring 10 cm 10 cm 1 cm is placed between two heat reservoirs maintained at temperatures of 10^ C and 90^ C . The larger surface areas of the slab are in contact A person's normal body-temperature is 97 ^ F . Determine the rate at which heat flows out of their body through the clothes, assuming the following values: room temperature = 47 ^ A steel rod ( K = 46 J s ⁻¹ m ⁻¹ ^ C ⁻¹ ) of length 1.0 m has one end kept in ice at 0^ C and the opposite end in boiling water at 100^ C . The rod has a cross-sectional area of 0.An icebox almost entirely filled with ice at 0^ C is submerged in a large volume of water at 20^ C . The walls of the box have a surface area of 2400 cm ^2 , a thickness of 2.0 mm Water is boiled in a container whose bottom has a surface area of 25 cm ^2 , a thickness of 1.0 mm , and a thermal conductivity of 50 W m ⁻¹ ^ C ⁻¹ . After boiling begins, 100 g ofA pitcher having 1 -mm thick porous walls holds 10 kg of water. Water reaches the outer surface and evaporates at a rate of 0.1 g s ⁻¹ . The surface area of the pitcher (one side) Forming three sides of a square, a steel frame ( K = 45 W m ⁻¹ ^ C⁻¹ ) has a total length of 60 cm and a cross sectional area of 0.20 cm ^2 . The two free ends are maintained at 20 Full Heat Transfer list All Concepts Of Physics MCQ Edition [Volume 2] PYQs