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1
JEE Main 2021 (Online) 17th March Morning Shift
MCQ (Single Correct Answer)
+4
-1
Two identical metal wires of thermal conductivities K1 and K2 respectively are connected in series. The effective thermal conductivity of the combination is :
A
$${{2{K_1}{K_2}} \over {{K_1} + {K_2}}}$$
B
$${{{K_1} + {K_2}} \over {{K_1}{K_2}}}$$
C
$${{{K_1} + {K_2}} \over {2{K_1}{K_2}}}$$
D
$${{{K_1}{K_2}} \over {{K_1} + {K_2}}}$$
2
JEE Main 2021 (Online) 17th March Morning Shift
MCQ (Single Correct Answer)
+4
-1
A Carnot's engine working between 400 K and 800 K has a work output of 1200 J per cycle. The amount of heat energy supplied to the engine from the source in each cycle is :
A
2400 J
B
1600 J
C
1800 J
D
3200 J
3
JEE Main 2021 (Online) 16th March Evening Shift
MCQ (Single Correct Answer)
+4
-1
Calculate the value of mean free path ($$\lambda$$) for oxygen molecules at temperature 27$$^\circ$$C and pressure 1.01 $$\times$$ 105 Pa. Assume the molecular diameter 0.3 nm and the gas is ideal. (k = 1.38 $$\times$$ 10$$-$$23 JK$$-$$1)
A
32 nm
B
58 nm
C
86 nm
D
102 nm
4
JEE Main 2021 (Online) 16th March Evening Shift
MCQ (Single Correct Answer)
+4
-1
A bimetallic strip consists of metals A and B. It is mounted rigidly as shown. The metal A has higher coefficient of expansion compared to that of metal B. When the bimetallic strip is placed in a cold bath, it will :

A
Neither bend nor shrink
B
Bend towards the left
C
Not bend but shrink
D
Bend towards the right
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