1
WB JEE 2021
MCQ (Single Correct Answer)
+2
-0.5
Change Language
Two metal wires of identical dimensions are connected in series. If $$\sigma$$1 and $$\sigma$$2 are the electrical conductivities of the metal wires respectively, the effective conductivity of the combination is
A
$$\sigma$$1 + $$\sigma$$2
B
$${{{\sigma _1}{\sigma _2}} \over {{\sigma _1} + {\sigma _2}}}$$
C
$${{2{\sigma _1}{\sigma _2}} \over {{\sigma _1} + {\sigma _2}}}$$
D
$${{{\sigma _1} + {\sigma _2}} \over {2{\sigma _1}{\sigma _2}}}$$
2
WB JEE 2021
MCQ (Single Correct Answer)
+2
-0.5
Change Language
A uniform rod of length L pivoted at one end P is freely rotated in a horizontal plane with an angular velocity $$\omega$$ about a vertical axis passing through P. If the temperature of the system is increased by $$\Delta$$T, angular velocity becomes $${\omega \over 2}$$. If coefficient of linear expansion of the rod is $$\alpha$$($$\alpha$$ << 1), then $$\Delta$$T will be
A
$${1 \over \alpha }$$
B
$${1 \over 2\alpha }$$
C
$${1 \over 4\alpha }$$
D
$$\alpha$$
3
WB JEE 2021
MCQ (Single Correct Answer)
+2
-0.5
Change Language
An ideal gas of molar mass M is contained in a very tall vertical cylindrical column in the uniform gravitational field. Assuming the gas temperature to be T, the height at which the centre of gravity of the gas is located is (R$$\to$$universal gas constant)
A
$${{RT} \over g}$$
B
$${{RT} \over Mg}$$
C
MgR
D
RTg
4
WB JEE 2021
MCQ (Single Correct Answer)
+2
-0.5
Change Language
Under isothermal conditions, two soap bubbles of radii a and b coalesce to form a single bubble of radius c. If the external pressure is p, then surface tension of the bubbles is
A
$${{p({c^3} - {a^3} + {b^3})} \over {4({a^2} + {b^2} - {c^2})}}$$
B
$${{p({c^3} - {a^3} - {b^3})} \over {4({a^2} + {b^2} - {c^2})}}$$
C
$${{p({c^2} + {a^3} - {b^2})} \over {4({a^3} + {b^3} - {c^3})}}$$
D
$${{p({a^3} + {b^3} - {c^3})} \over {4({a^2} + {b^2} - {c^2})}}$$
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