1
JEE Main 2021 (Online) 26th February Morning Shift
MCQ (Single Correct Answer)
+4
-1
Change Language
An alternating current is given by the equation i = i1 sin $$\omega$$t + i2 cos $$\omega$$t. The rms current will be :
A
$${1 \over {\sqrt 2 }}{\left( {i_1^2 + i_2^2} \right)^{{1 \over 2}}}$$
B
$${1 \over {\sqrt 2 }}({i_1} + {i_2})$$
C
$${1 \over {\sqrt 2 }}{({i_1} + {i_2})^2}$$
D
$${1 \over 2}{\left( {i_1^2 + i_2^2} \right)^{{1 \over 2}}}$$
2
JEE Main 2021 (Online) 26th February Morning Shift
MCQ (Single Correct Answer)
+4
-1
Change Language
Four identical solid spheres each of mass 'm' and radius 'a' are placed with their centres on the four corners of a square of side 'b'. The moment of inertia of the system about one side of square where the axis of rotation is parallel to the plane of the square is :
A
$${4 \over 5}m{a^2}$$
B
$${8 \over 5}m{a^2} + m{b^2}$$
C
$${4 \over 5}m{a^2} + 2m{b^2}$$
D
$${8 \over 5}m{a^2} + 2m{b^2}$$
3
JEE Main 2021 (Online) 26th February Morning Shift
MCQ (Single Correct Answer)
+4
-1
Change Language
A large number of water drops, each of radius r, combine to have a drop of radius R. If the surface tension is T and mechanical equivalent of heat is J, the rise in heat energy per unit volume will be :
A
$${{2T} \over J}\left( {{1 \over r} - {1 \over R}} \right)$$
B
$${{3T} \over J}\left( {{1 \over r} - {1 \over R}} \right)$$
C
$${{3T} \over rJ}$$
D
$${{2T} \over rJ}$$
4
JEE Main 2021 (Online) 26th February Morning Shift
MCQ (Single Correct Answer)
+4
-1
Change Language
LED is constructed from Ga-As-P semiconducting material. The energy gap of this LED is 1.9 eV. Calculate the wavelength of light emitted and its colour.

[h = 6.63 $$\times$$ 10$$-$$34 Js and c = 3 $$\times$$ 108 ms$$-$$1]
A
654 nm and orange colour
B
654 nm and red colour
C
1046 nm and red colour
D
1046 nm and blue colour
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