1
JEE Main 2019 (Online) 9th January Evening Slot
+4
-1
Two point charges q1$$\left( {\sqrt {10} \mu C} \right)$$ and q2($$-$$ 25 $$\mu$$C) are placed on the x-axis at x = 1 m and x = 4 m respectively. The electric field (in V/m) at a point y = 3 m on y-axis is,
[take $${1 \over {4\pi { \in _0}}}$$ = 9 $$\times$$ 109 Nm2C$$-$$2]
A
$$\left( {63\widehat i - 27\widehat j} \right) \times {10^2}$$
B
$$\left( { - 63\widehat i + 27\widehat j} \right) \times {10^2}$$
C
$$\left( {81\widehat i - 81\widehat j} \right) \times {10^2}$$
D
$$\left( { - 81\widehat i + 81\widehat j} \right) \times {10^2}$$
2
JEE Main 2019 (Online) 9th January Evening Slot
+4
-1
Charge is distributed within a sphere of radius R with a volume charge density $$\rho \left( r \right) = {A \over {{r^2}}}{e^{ - {{2r} \over s}}},$$ where A and a are constants. If Q is the total charge of this charge distribution, the radius R is :
A
a log $$\left( {1 - {Q \over {2\pi aA}}} \right)$$
B
$${a \over 2}$$ log $$\left( {{1 \over {1 - {Q \over {2\pi aA}}}}} \right)$$
C
a log $$\left( {{1 \over {1 - {Q \over {2\pi aA}}}}} \right)$$
D
$${a \over 2}$$ log $$\left( {1 - {Q \over {2\pi aA}}} \right)$$
3
JEE Main 2019 (Online) 9th January Morning Slot
+4
-1
Three charges + Q, q, + Q are placed respectively, at distance, 0, d/2 and d from the origin, on the x-axis. If the net force experienced by + Q, placed at x = 0, is zero, then value of q is :
A
$$-$$ $${Q \over 4}$$
B
+ $${Q \over 2}$$
C
+ $${Q \over 4}$$
D
$$-$$ $${Q \over 2}$$
4
JEE Main 2019 (Online) 9th January Morning Slot
+4
-1
For a uniformly charged ring of radius R, the electric field on its axis has the largest magnitude at a distance h from its center. Then value of h is :
A
$${R \over {\sqrt 5 }}$$
B
$${R \over {\sqrt 2 }}$$
C
R
D
R$$\sqrt 2$$
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