1
JEE Main 2021 (Online) 17th March Morning Shift
MCQ (Single Correct Answer)
+4
-1
Change Language
If an electron is moving in the nth orbit of the hydrogen atom, then its velocity (vn) for the nth orbit is given as :
A
$${v_n} \propto {1 \over n}$$
B
vn $$ \propto $$ n2
C
vn $$ \propto $$ n
D
$${v_n} \propto {1 \over {{n^2}}}$$
2
JEE Main 2021 (Online) 17th March Morning Shift
MCQ (Single Correct Answer)
+4
-1
Change Language
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
$${{{K_1}{K_2}} \over {{K_1} + {K_2}}}$$
3
JEE Main 2021 (Online) 17th March Morning Shift
MCQ (Single Correct Answer)
+4
-1
Change Language
A triangular plate is shown. A force $$\overrightarrow F $$ = 4$$\widehat i$$ $$-$$ 3$$\widehat j$$ is applied at point P. The torque at point P with respect to point 'O' and 'Q' are :

JEE Main 2021 (Online) 17th March Morning Shift Physics - Rotational Motion Question 83 English
A
$$-$$ 15 + 20$$\sqrt 3 $$, 15 + 20$$\sqrt 3 $$
B
15 $$-$$ 20$$\sqrt 3 $$, 15 + 20$$\sqrt 3 $$
C
15 + 20$$\sqrt 3 $$, 15 $$-$$ 20$$\sqrt 3 $$
D
$$-$$ 15 $$-$$ 20$$\sqrt 3 $$, 15 $$-$$ 20$$\sqrt 3 $$
4
JEE Main 2021 (Online) 17th March Morning Shift
MCQ (Single Correct Answer)
+4
-1
Change Language
When two soap bubbles of radii a and b (b > a) coalesce, the radius of curvature of common surface is :
A
$${{b - a} \over {ab}}$$
B
$${{a + b} \over {ab}}$$
C
$${{ab} \over {a + b}}$$
D
$${{ab} \over {b - a}}$$
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