WB JEE 2017 | Electrostatics Question 31 | Physics

WB JEE 2017

MCQ (Single Correct Answer)

-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)

$${Q \over {6{\varepsilon _0}}}$$

$$4\pi Q$$

$${Q \over {4\pi {\varepsilon _0}}}$$

$${Q \over {6\pi {\varepsilon _0}}}$$

WB JEE 2017

MCQ (Single Correct Answer)

-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

Q₁ = Q₂ = 0.4 C

Q₁ $$ \approx $$ 0.8 C, Q₂ negligible

Q₁ negligible, Q₂ $$\approx $$ 0.8 C

Q₁ = 0.2 C, Q₂ = 0.6 C

WB JEE 2017

MCQ (Single Correct Answer)

-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

$$2\sqrt {gR} $$

$$\sqrt {2gR} $$

$$\sqrt {5gR} $$

WB JEE 2017

MCQ (Single Correct Answer)

-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

come back to its original position and stay there

execute oscillations with frequency $${1 \over {2\pi }}\sqrt {{Q \over {2\pi {\varepsilon _0}M{a^3}}}} $$

fly to infinity

execute oscillations with frequency $${1 \over {2\pi }}\sqrt {{Q \over {2\pi {\varepsilon _0}M{a^2}}}} $$

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