1
JEE Main 2019 (Online) 12th April Evening Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
Let a total charge 2Q be distributed in a sphere of radius R, with the charge density given by $$\rho $$(r) = kr, where r is the distance from the centre. Two charges A and B, of –Q each, are placed on diametrically opposite points, at equal distance, $$a$$ from the centre. If A and B do not experience any force, then :
A
$$a = {8^{ - 1/4}}R$$
B
$$a = {2^{ - 1/4}}R$$
C
$$a = {{3R} \over {{2^{1/4}}}}$$
D
$$a = {R \over {\sqrt 3 }}$$
2
JEE Main 2019 (Online) 12th April Evening Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
Consider the LR circuit shown in the figure. If the switch S is closed at t = 0 then the amount of charge that passes through the battery between t = 0 and t = $${L \over R}$$ is : JEE Main 2019 (Online) 12th April Evening Slot Physics - Alternating Current Question 141 English
A
$${{2.7EL} \over {{R^2}}}$$
B
$${{EL} \over {2.7{R^2}}}$$
C
$${{7.3EL} \over {{R^2}}}$$
D
$${{EL} \over {7.3{R^2}}}$$
3
JEE Main 2019 (Online) 12th April Evening Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
Consider an electron in a hydrogen atom revolving in its second excited state (having radius 4.65 $$\mathop A\limits^o $$). The de-Broglie wavelength of this electron is :
A
6.6 $$\mathop A\limits^o $$
B
3.5 $$\mathop A\limits^o $$
C
9.7 $$\mathop A\limits^o $$
D
12.9 $$\mathop A\limits^o $$
4
JEE Main 2019 (Online) 12th April Evening Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
One kg of water, at 20oC, heated in an electric kettle whose heating element has a mean (temperature averaged) resistance of 20 $$\Omega $$. The rms voltage in the mains is 200 V. Ignoring heat loss from the kettle, time taken for water to evaporate fully, is close to : [Specific heat of water = 4200 J/(kg oC), Latent heat of water = 2260 kJ/kg]
A
10 minutes
B
22 minutes
C
3 minutes
D
16 minutes
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