1
WB JEE 2018
+2
-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? A
$$2\pi \sqrt {{L \over {\left( {g - {{mq} \over {{\varepsilon _0}\sigma }}} \right)}}}$$
B
$$\sqrt {{L \over {\left( {g - {{mq\sigma } \over {{\varepsilon _0}}}} \right)}}}$$
C
$${1 \over {2\pi }}\sqrt {{L \over {\left( {g - {{q\sigma } \over {{\varepsilon _0}m}}} \right)}}}$$
D
$$2\pi \sqrt {{L \over {\left( {g - {{q\sigma } \over {{\varepsilon _0}m}}} \right)}}}$$
2
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
$${Q \over {6\pi {\varepsilon _0}}}$$
3
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
4
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
$$\sqrt {5gR}$$
WB JEE Subjects
Physics
Mechanics
Electricity
Optics
Modern Physics
Chemistry
Physical Chemistry
Inorganic Chemistry
Organic Chemistry
Mathematics
Algebra
Trigonometry
Coordinate Geometry
Calculus
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