JEE Advanced | 2014Heat TransferHard
Question
Heater of an electric kettle is made of a wire of length L and diameter d. It takes 4 minutes to raise the temperature of 0.5 kg water by 40 K. This heater is replaced by a new heater having two wires of the same material, each of length L and diameter 2d. The way these wires are connected is given in the options. How much time in minutes will it take to raise the temperature of the same amount of water by 40 K?
Options
A.4 if wires are in parallel
B.2 if wires are in series
C.1 if wires are in series
D.0.5 if wires are in parallel
Solution
t = 
⇒ t ∝ R. R =( ρl / A), R′ =
(as d′ = 2d)
When wires are in series, R1 = R′ + R′ = 2R′ =
⇒ t′ = 
= 2 min
When wires are in parallel, R2 =
⇒ t′ = 
= 0.5 min
⇒ t ∝ R. R =( ρl / A), R′ =
(as d′ = 2d)When wires are in series, R1 = R′ + R′ = 2R′ =
⇒ t′ = = 2 minWhen wires are in parallel, R2 =
⇒ t′ = = 0.5 minCreate a free account to view solution
View Solution FreeMore Heat Transfer Questions
If the rates of loss of energy by unit area of an iron ball are E1 E2 and E3 when it cools from 75oC to 70oC, 70oC to 65...Which of the following statements is/are true ?...In a dark room with ambient temperature T0, a black body is kept at a temperature T. Keeping the temperature of the blac...Radius of two spheres of same material are 1 & 4 m respectively and their temp. are 4 × 103 and 2 × 103 K resp...Increasing the temperature of a black body wavelength for maximum emission....