1
WB JEE 2017
+1
-0.25
A positive charge Q is situated at the centre of a cube. The electric flux through any face of the cube is (in SI units)
A
$${Q \over {6{\varepsilon _0}}}$$
B
$$4\pi Q$$
C
$${Q \over {4\pi {\varepsilon _0}}}$$
D
$${Q \over {6\pi {\varepsilon _0}}}$$
2
WB JEE 2017
+1
-0.25
A charge of 0.8 coulomb is divided into two charges Q1 and Q2. These are kept at a separation of 30 cm. The force on Q1 is maximum when
A
Q1 = Q2 = 0.4 C
B
Q1 $$\approx$$ 0.8 C, Q2 negligible
C
Q1 negligible, Q2 $$\approx$$ 0.8 C
D
Q1 = 0.2 C, Q2 = 0.6 C
3
WB JEE 2017
+2
-0.5
A particle with charge Q coulomb, tied at the end of an inextensible string of length R metre, revolves in a vertical plane. At the centre of the circular trajectory, there is a fixed charge of magnitude Q coulomb. The mass of the moving charge M is such that $$Mg = {{{Q^2}} \over {4\pi {\varepsilon _0}{R^2}}}$$. If at the highest position of the particle, the tension of the string just vanishes, the horizontal velocity at the lowest point has to be
A
0
B
$$2\sqrt {gR}$$
C
$$\sqrt {2gR}$$
D
$$\sqrt {5gR}$$
4
WB JEE 2017
+2
-0.5
A unit negative charge with mass M resides at the mid-point of the straight line of length 2a adjoining two fixed charges of magnitude +Q each. If it is given a very small displacement x(x << a) in a direction perpendicular to the straight line, it will
A
come back to its original position and stay there
B
execute oscillations with frequency $${1 \over {2\pi }}\sqrt {{Q \over {2\pi {\varepsilon _0}M{a^3}}}}$$
C
fly to infinity
D
execute oscillations with frequency $${1 \over {2\pi }}\sqrt {{Q \over {2\pi {\varepsilon _0}M{a^2}}}}$$
EXAM MAP
Medical
NEET