1
JEE Main 2020 (Online) 4th September Evening Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
A series L-R circuit is connected to a battery of emf V. If the circuit is switched on at t = 0, then the time at which the energy stored in the inductor reaches $$\left( {{1 \over n}} \right)$$ times of its maximum value, is :
A
$${L \over R}\ln \left( {{{\sqrt n } \over {\sqrt n + 1}}} \right)$$
B
$${L \over R}\ln \left( {{{\sqrt n } \over {\sqrt n - 1}}} \right)$$
C
$${L \over R}\ln \left( {{{\sqrt n + 1} \over {\sqrt n - 1}}} \right)$$
D
$${L \over R}\ln \left( {{{\sqrt n - 1} \over {\sqrt n }}} \right)$$
2
JEE Main 2020 (Online) 4th September Evening Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
Match the thermodynamic processes taking place in a system with the correct conditions. In the table : $$\Delta $$Q is the heat supplied, $$\Delta $$W is the work done and $$\Delta $$U is change in internal energy of the system.

Process Condition
(I) Adiabatic (1) $$\Delta $$W = 0
(II) Isothermal (2) $$\Delta $$Q = 0
(III) Isochoric (3) $$\Delta $$U $$ \ne $$ 0, $$\Delta $$W $$ \ne $$ 0, $$\Delta $$Q $$ \ne $$ 0
(IV) Isobaric (4) $$\Delta $$U = 0
A
(I) - (1), (II) - (1), (III) - (2), (IV) - (3)
B
(I) - (2), (II) - (4), (III) - (1), (IV) - (3)
C
(I) - (1), (II) - (2), (III) - (4), (IV) - (4)
D
(I) - (2), (II) - (1), (III) - (4), (IV) - (3)
3
JEE Main 2020 (Online) 4th September Evening Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
A small ball of mass m is thrown upward with velocity u from the ground. The ball experiences a resistive force mkv2 where v is its speed. The maximum height attained by the ball is :
A
$${1 \over k}{\tan ^{ - 1}}{{k{u^2}} \over {2g}}$$
B
$${1 \over {2k}}{\tan ^{ - 1}}{{k{u^2}} \over g}$$
C
$${1 \over {2k}}\ln \left( {1 + {{k{u^2}} \over g}} \right)$$
D
$${1 \over k}\ln \left( {1 + {{k{u^2}} \over {2g}}} \right)$$
4
JEE Main 2020 (Online) 4th September Evening Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
A circular coil has moment of inertia 0.8 kg m2 around any diameter and is carrying current to produce a magnetic moment of 20 Am2 . The coil is kept initially in a vertical position and it can rotate freely around a horizontal diameter. When a uniform magnetic field of 4 T is applied along the vertical,it starts rotating around its horizontal diameter. The angular speed the coil acquires after rotating by 60o will be:
A
10 $$\pi $$ rad s–1
B
20 $$\pi $$ rad s–1
C
$$10{\left( 3 \right)^{1/4}}$$ rad s–1
D
20 rad s–1
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