Electrostatics PYQs Set 5 (PDF)

Set 5 of 12 · Questions 121-150 of 349

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Mere Teacher · Previous Year Questions NEET Physics · Electrostatics · Set 5 (Q121-150)
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121. $The flux of the electric field E = 24 i + 30 j + 28 k NC^{- 1} through an area of 20 m^{2} on the yz plane is$ (1) $480 Nm^{2} C^{- 1}$ (2) $600 Nm^{2} C^{- 1}$ (3) $560 Nm^{2} C^{- 1}$ (4) $1640 Nm^{2} C^{- 1}$ 122. $The potential of the electric field produced by a point charge at any point (x, y, z) is given by V = 3 x^{2} + 5, where x, y, z are in meters and V is in volts. The intensity of the electric field at (- 2, 1, 0) is$ (1) $+ 17 V m^{- 1}$ (2) $- 17 V m^{- 1}$ (3) $+ 12 V m^{- 1}$ (4) $- 12 V m^{- 1}$ 123. $The magnitude of point charge due to which the electric field 30 cm away has the magnitude 2 N C^{- 1} will be$ (1) $2 \times 10^{- 11} C$ (2) $3 \times 10^{- 11} C$ (3) $5 \times 10^{- 11} C$ (4) $9 \times 10^{- 11} C$ 124. $If V is the gravitational potential due to sphere of uniform density on its surface, then its value at the centre of sphere will be:$ (1) $\frac{4}{3} V$ (2) $\frac{V}{2}$ (3) $V$ (4) $\frac{3 V}{2}$ 125. $A system of 2 capacitors of capacitance 2 μF and 4 μF is connected in series across a potential difference of 6 V . The electric charge and energy stored in the system are$ (1) $1 μC and 3 μJ$ (2) $8 μC and 24 μJ$ (3) $10 μC and 30 μJ$ (4) $36 μC and 108 μJ$ 126. $Electric potential due to a space is given by φ (x, y, z) = φ_{0} \frac{x _{0}}{x}; when x_{0} = 5 m and φ_{0} = 8 V . Find the electric field at (10 m, 5 m, 5 m)$ (1) $0.40 Vm^{- 1} i$ (2) $- 0.40 Vm^{- 1} i$ (3) $4.0 Vm^{- 1} i$ (4) $- 4.0 Vm^{- 1} i$ 127. $Two fixed charges A and B of 5 μC each are separated by a distance of 6 m . C is the mid point of the line joining A and B. A charge ' Q ' of - 5 μC is shot perpendicular to the line joining A and B through C with a kinetic energy of 0.06 J . The charge ' Q' comes to rest at a point D. The distance CD is$ (1) $3 m$ (2) $3 m$ (3) $33 m$ (4) $4 m$ 128. $A hollow metal sphere of radius R is uniformly charged. The electric field due to the sphere at a distance r from the center$ (1) $decreases a sr increases for r<R and for r>R$ (2) $increases a sr increases for r<R and for r>R$ (3) $zero as r increases for r < R, decreases as r increases for r > R$ (4) $zero a sr increases for r < R, increases as r increases for r > R$ 129. $Two-point charges of 1 nC and 2 nC are placed at the two corners of equilateral triangle of side 3 cm. The work done in bringing a charge of 3 nC from infinity to the third corner of the triangle is μJ . \frac{1}{4 π ϵ _{0}} = 9 \times 10^{9} N . \frac{m ^{2}}{C ^{2}}$ (1) $27$ (2) $5.4$ (3) $2.7$ (4) $3.3$ 130. $A hot filament liberates an electron with zero initial velocity. The anode potential is 1200 V . The speed of the electron when it strikes the anode is$ (1) $2.1 \times 10^{7} m s^{- 1}$ (2) $2.5 \times 10^{8} m s^{- 1}$ (3) $1.5 \times 10^{5} m s^{- 1}$ (4) $2.5 \times 10^{6} m s^{- 1}$ 131. $Two conducting spheres of radii r_{1} and r_{2} are charged to the same surface charge density. The ratio of electric fields near their surfaces is$ (1) $\frac{r _{1}^{2}}{r _{2}^{2}}$ (2) $\frac{r _{2}^{2}}{r _{1}^{2}}$ (3) $\frac{r _{1}}{r _{2}}$ (4) $1 : 1$ 132. $A certain charge 2Q is divided at first into two parts q_{1} and q_{2} . Later the charges are placed at a certain distance. If the force of interaction between two charges is maximum then \frac{Q}{q _{1}} =$ (1) $1$ (2) $4$ (3) $0.5$ (4) $2$ 133. $A ball of mass 1 g having a charge of 20 μC is tied to one end of a string of length 0.9 m can rotate in a vertical plane in a uniform electric field 100 NC^{- 1} directed upwards. The minimum horizontal velocity that must be given to the ball at the lowest position so that it completes the vertical circle is (Let, g = 10 ms^{- 2})$ (1) $9 ms^{- 1}$ (2) $18 ms^{- 1}$ (3) $36 ms^{- 1}$ (4) $6 ms^{- 1}$ 134. $Two capacitors of capacity 4 μF and 6 μF are connected in series to a 500 V battery. The potential difference across 4 μF capacitor is$ (1) $200 V$ (2) $300 V$ (3) $400 V$ (4) $500 V$ 135. $A short electric dipole has a dipole moment of 16 \times 10^{- 9} C - m . The electric potential due to the dipole at a point at a distance of 0.6 m from the centre of the dipole, situated on a line making an angle of 60^{\circ} with the dipole axis is (\frac{1}{4 π ϵ _{0}} = 9 \times 10^{9} Nm^{2} / C^{2}) [NEET 2020]$ (1) $200 V$ (2) $400 V$ (3) $zero$ (4) $50 V$ 136. $The electric field due to a short electric dipole at a large distance (r) from center of dipole on the equatorial plane varies with distance as:$ (1) $r$ (2) $\frac{1}{r ^{2}}$ (3) $\frac{1}{r ^{3}}$ (4) $\frac{1}{r}$ 137. $A small block of mass 5 g and charge 5 μC is placed on insulated, frictionless, inclined plane of angle 60^{\circ} . An electric field is applied parallel to the inclined plane. If the block remains at rest then the magnitude of electric field is [ Take (g = 10 m / s^{2})$ (1) $\frac{10 ^{5}}{3} N / C$ (2) $\frac{5}{3} \times 10^{4} N / C$ (3) $3 \times 10^{4} N / C$ (4) $None$ 138. $The electric field intensity at a point near and outside the surface of a charged conductor of any shape is ' E_{1}'. The electric field intensity due to uniformly charged infinite thin plane sheet is ' E_{2}'. The relation between ' E_{1}' and ' E_{2}' is$ (1) $2 E_{1} = E_{2}$ (2) $E_{1} = E_{2}$ (3) $E_{1} = 2 E_{2}$ (4) $E_{1} = 4 E_{2}$ 139. $An electric dipole with dipole moment 4 \times 10^{- 9} Cm is aligned at 30^{\circ} with the direction of a uniform electric field of magnitude 5 \times 10^{4} N C^{- 1}, the magnitude of the torque acting on the dipole is$ (1) $10^{- 5} N m$ (2) $10^{- 4} N m$ (3) $10 \times 10^{- 3} N m$ (4) $3\times 10^{- 4} N m$ 140. $An electric dipole of moment p = (- i^- 3 j^+ 2 k^) \times 1 0^{- 29} C.m. is at the origin (0, 0, 0). The electric field due to this dipole at r = (+ i^+ 3 j^+ 5 k^) (note that r . p = 0) is parallel to :$ (1) $(+ i^+ 3 j^- 2 k^)$ (2) $(- i^+ 3 j^- 2 k^)$ (3) $(+ i^- 3 j^- 2 k^)$ (4) $(- i^- 3 j^+ 2 k^)$ 141. $An electric dipole of moment p is placed in an electric field of intensity E. The dipole acquires a position such that the axis of the dipole makes an angle 6 with the direction of the field. Assuming that the potential energy of the dipole to be zero when Θ = 9 0^{o}, the torque and the potential energy of the dipole will respectively be$ (1) $pE sin Θ,-pE cos Θ$ (2) $pE sin Θ,-2pE cos Θ$ (3) $pE sin Θ,2pE cos Θ$ (4) $pE cos Θ,-pE sin Θ$ 142. $A charged cylinder of radius 3 mm has surface charge density 4 μC / m^{2} . It is placed in a medium of dielectric constant 628. The electric intensity at a point at a distance of 1.5 m from its axis is$ (1) $1.44 V / m$ (2) $2.44 V / m$ (3) $3 V / m$ (4) $0.5 V / m$ 143. $An electric dipole is placed at an angle of 30º with an electric field intensity 2 \times 1 0^{5} N/C. It experiences a torque equal to 4 N m. The charge on the dipole, if the dipole length is 2cm, is$ (1) $7 µC$ (2) $8 mC$ (3) $2 mC$ (4) $5 mC$ 144. $An electrician requires a capacitance of 6 μF in a circuit across a potential difference of 1.5 kV . A large number of 2 μF capacitors which can withstand a potential difference of not more than 500 V are available. The minimum number of capacitors required for the purpose is$ (1) $3$ (2) $9$ (3) $6$ (4) $27$ 145. $The minimum work needed to be done to bring a charge q = 6 μC from \infty to a point 0.75 m from a charge Q = 30 μC is$ (1) $4.16 J$ (2) $5.16 J$ (3) $2.16 J$ (4) $1.16 J$ 146. $A region contains a uniform electric field E = (10 i + 30 j) Vm^{- 1} \cdot A and B are two points in the field at (1, 2, 0) m and (2, 1, 3) m, respectively. The work done when a charge of 0.8 C moves from A to B in a parabolic path is$ (1) $8 J$ (2) $80 J$ (3) $40 J$ (4) $16 J$ 147. $An electric dipole is placed at an angle of 30 ° with an electric field intensity 2 \times 1 0^{5} N C^{- 1} . It experiences a torque equal to 4 Nm . The charge on the dipole, if the dipole length is 2 cm, is$ (1) $8 mC$ (2) $2 mC$ (3) $5 mC$ (4) $7 μC$ 148. $The vehicles carrying inflammable fluids usually have metallic chains touching the ground:$ (1) $To protect tyres from catching dirt from ground$ (2) $To alert other vehicles$ (3) $It is a custom$ (4) $To conduct excess charge due to air friction to ground and prevent sparking$ 149. $A bullet of mass 2g is having a charge of 2 μC . Through what potential difference must it be accelerated, starting from rest, to acquire a speed of10 m/s 7.$ (1) $5kV$ (2) $50kV$ (3) $5V$ (4) $50V$ 150. $At what temperature a gold ring of diameter 6.230 cm be heated so that it can be fitted on a wooden bangle of diameter 6.241 cm? Both the diameters have been measured at room temperature (27°C). (Given: coefficient of linear thermal expansion of gold α_{L} = 1.4 \times 1 0^{- 5} K^{- 1})$ (1) $125.7°C$ (2) $91.7°C$ (3) $425.7°$ (4) $152.7°C$