Heat & Thermodynamics · JEE Main previous year questions

The temperature of the two outer surfaces of a composite slab, consisting of two materials having coefficients of thermal conductivity $K$ and $2K$ and thickness $x$ and $4x$, respectively, are $T_2$ and $T_1(T_2>T_1)$. The rate of heat transfer through the slab, in a steady state is $\left(\frac{A(T_2-T_1)K}{x}\right)f$, with $f$ equal to

1. A.$\frac{2}{3}$
2. B.$\frac{1}{2}$
3. C.$1$
4. D.$\frac{1}{3}$

Infrared radiation is detected by

1. A.spectrometer
2. B.pyrometer
3. C.nanometer
4. D.photometer

Which of the following is more close to a black body?

1. A.black board paint
2. B.green leaves
3. C.black holes
4. D.red roses

Even Carnot engine cannot give $100\%$ efficiency because we cannot

1. A.prevent radiation
2. B.find ideal sources
3. C.reach absolute zero temperature
4. D.eliminate friction.