WB JEE 2018 | Electrostatics Question 21 | Physics

WB JEE 2018

MCQ (Single Correct Answer)

-0.25

A point charge $$-$$ q is carried from a point A to another point B on the axis of a charged ring of radius r carrying a charge + q. If the point A is at a distance $${4 \over 3}r$$ from the centre of the ring and the point B is $${3 \over 4}r$$ from the centre but on the opposite side, what is the net work that need to be done for this?

$$ - {7 \over 5}\,.\,{{{q^2}} \over {4\pi {\varepsilon _0}r}}$$

$$ - {1 \over 5}\,.\,{{{q^2}} \over {4\pi {\varepsilon _0}r}}$$

$${7 \over 5}\,.\,{{{q^2}} \over {4\pi {\varepsilon _0}r}}$$

$${1 \over 5}\,.\,{{{q^2}} \over {4\pi {\varepsilon _0}r}}$$

WB JEE 2018

MCQ (Single Correct Answer)

-0.25

Consider a region in free space bounded by the surfaces of an imaginary cube having sides of length a as shown in the figure. A charge + Q is placed at the centre O of the cube. P is such a point outside the cube that the line OP perpendicularly intersects the surface ABCD at R and also OR = RP = a/2. A charge + Q is placed at point P also. What is the total electric flux through the five faces of the cube other than ABCD?

WB JEE 2018 Physics - Electrostatics Question 18 English

WB JEE 2018 Physics - Electrostatics Question 18 English

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

$${5Q \over {{6\varepsilon _0}}}$$

$${10Q \over {{6\varepsilon _0}}}$$

zero

WB JEE 2018

MCQ (Single Correct Answer)

-0.25

Four equal charges of value + Q are placed at any four vertices of a regular hexagon of side 'a'. By suitably choosing the vertices, what can be maximum possible magnitude of electric field at the centre of the hexagon?

$${Q \over {4\pi {\varepsilon _0}{a^2}}}$$

$${{\sqrt 2 Q} \over {4\pi {\varepsilon _0}{a^2}}}$$

$${{\sqrt 3 Q} \over {4\pi {\varepsilon _0}{a^2}}}$$

$${{2Q} \over {4\pi {\varepsilon _0}{a^2}}}$$

WB JEE 2018

MCQ (Single Correct Answer)

-0.5

The bob of a pendulum of mass m, suspended by an inextensible string of length L as shown in the figure carries a small charge q. An infinite horizontal plane conductor with uniform surface charge density $$\sigma$$ is placed below it. What will be the time period of the pendulum for small amplitude oscillations?

WB JEE 2018 Physics - Electrostatics Question 21 English

WB JEE 2018 Physics - Electrostatics Question 21 English

$$2\pi \sqrt {{L \over {\left( {g - {{mq} \over {{\varepsilon _0}\sigma }}} \right)}}} $$

$$\sqrt {{L \over {\left( {g - {{mq\sigma } \over {{\varepsilon _0}}}} \right)}}} $$

$${1 \over {2\pi }}\sqrt {{L \over {\left( {g - {{q\sigma } \over {{\varepsilon _0}m}}} \right)}}} $$

$$2\pi \sqrt {{L \over {\left( {g - {{q\sigma } \over {{\varepsilon _0}m}}} \right)}}} $$

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