Important questions of Chapter-2 class 12th
Electrostatic Potential and Capacitance
Questions on Electric potential, potential difference and work.
Q. 1 The potential difference between two points is 10 V how much work will be done in carrying a charge of 200 µC from one point to the other point.
Ans. 2 x 10^-3J
Q. 2 What is the electric potential at the surface of a gold nucleus of diameter 13.2 fermi. Z for gold is 79.
Ans. 1.7 x 10^7 volt.
Q.3 If 20 J of work has to be done to move an electric charge of 4 C from a point, where potential is 10 V to another point, where potential is V volt, find the value of V.
Ans. 15V .
Q.4 The electric potential at 0.1 m from a point charge is +50 V. What is the magnitude and sign of the charge.
Ans. 0.55 x 10^ -9 C and positive.
Q.5 A wire is bent in a circle of radius 10 cm it is given a charge of 250 µC which spreads on it uniformly. What is the electric potential at Centre?
Ans. 2.25 x 10^ 7 volt.
Question on potential due to system of charges
Q.6 Two charges 5 x 10^-8 C and -3 x 10^-8 C are located 16 cm apart. At what point on the line joining the two charges is the electric potential zero? Take the potential at infinity to be zero.
Ans. X = 10cm .
Q.7 A regular hexagon of side 10 cm has a charge 5 µC at each of its vertices. Calculate the potential at centre of the hexagon.
Ans. V = 2.7 x 10^6 v.
Q.8 A cube of side b has a charge q at each of its vertices. Determine the potential and electric field due to this charge array at the centre of the cube.
Ans. V = 8kq /b root3/2 and E = 0
Questions on Potential due to dipole -
Q.9 A short electric dipole has dipole moment of 4 x 10^-9 Cm. Find the following- (a) Electric potential at a distance 3 m from centre of the dipole on the axial line. b) Electric potential at a point distance 1 m from centre of dipole on the equatorial line. c) Electric potential at a distance 3 m from the centre of dipole making an angle of 30° with the dipole axis. Ans. a) 4V b) 0 c) 2 √3V
Q.10 Two charges 2 micro C and -2 micro C are placed at points A and B 6cm apart. Find the potential at axial point 2m away from centre of dipole. Ans. 270 V
Questions on potential gradient & electric field
Q.11 A small Particle carrying a negative charge of 1.6x 10^-19C is suspended in equilibrium between the horizontal metal plates 5 cm apart, having a potential differences of 3000 V across them. Find the mass of the particle.
Ans. m= 9.8 x 10^-16kg.
Q.12 A uniform Electric field of 10 N/C exists in a vertically downward direction. Find the increase in the electric potential as one goes up through a height of 150 cm. Ans 15V
Questions on potential due to continuous charge distribution
Q.13 Find potential at point P on axial line of uniformly charged rod of length L having linear charge density λ. When P lies at a distance A from rod.
Q.14 Find potential at axis and centre due to uniformly charged circular ring.
Q.15 Four equal charges q are placed at the corners of square of side a. Find out potential energy of charge system.
Questions on Potential difference & energy
Q.16 Find the change in potential energy of an electron when it moved through a potential difference of 1V. ( 1eV= 1.6x10^-19J)
Q.17 Find the self-energy of a charged spherical shell having charge Q and radius R. ( kQ²/ 2R)
Q.18 Find the amount of work done in rotating an electric dipole, of dipole moment 3.2 x 10^-8 Cm, from its position of stable equilibrium, to the unstable equilibrium , in a uniform electric field of intensity 10^4 N/C. (6.4 x 10^-4J)
Q.19 An electric dipole consists of two opposite charges each of magnitude 1 microC, separated by 2 cm. The dipole is placed in external uniform field of 10^5 N/C intensity. Find i) maximum torque exerted by the field on the dipole, and ii) work done in rotating the dipole through 180° starting from the position theta = 0°. Ans. i) 2 x 10^-3 ii) 4 x 10^-3
Q.20 An electric dipole of length 4cm, when placed with its axis making an angle of 60° with a uniform electric field experiences a torque of 4 root3 Nm. Calculate the potential energy of the dipole , if the dipole has charge of 8nC. Ans. -4J
Questions on capacitor
Q.21 Find the radius of a spherical conductor whose capacitance is 1 F. (9x10^9m)
Q.22 An isolated sphere has a capacitance 50pF. I) Calculate its radius II) How much charge should be placed on it to raise its potential to 10^4 V. (4.5cm, 0.5microC)
Q. 23 Twenty seven spherical drops of radius 3mm and carrying 10^-12 C of charge are combined to form a single drop. Find the capacitance and the potential of the bigger drop. ( 1pF, 27V)
Q.24 A Parallel plate capacitor has a plate area A and distance between two plates ‘d’. The capacitor is connected to a 4V battery. If the separation between the plates is reduced to half, what extra charge is given by battery to the positive plate? Ans. 4 ε0A/d
Q.25 A parallel plate capacitor has a capacitance C. If the charges of the plates are Q and -3Q, find the i) charges at the inner surfaces of the plates. ii) potential difference between the plates iii) charge flown if the plates are connected. Ans. 2Q, 2Q/C , 2Q or -2Q
Q.26 Two parallel plates, separated by 2mm of air have a capacitance of 3×10^-14 F and are charged to a potential of 200 V. Then without touching the plates, they are moved apart till the separation is 6mm. Find the work required to do so. ( 12 x 10^-10J)
Q.27 12microF and 4microF connected in series with 12V battery Find Ceq , Q released from cell, Q on each capacitor, V in each capacitor. Ans. 3 microF, 36microC, 36microC on each and 3V,9V
Q.28 2µF, 3 µF, 5 µF are connected in parallel with 4V battery. Find Ceq, Q released from cell, Q on each capacitor and V in each capacitor. Ans. 10 µF, 40 µC , 8 µC/ 12 µC/20 µC, 4V on each C.
Q.29 A slab of material of dielectric constant K has the same area as the plates of a parallel plate capacitor of capacitance C0 but has thickness d/2, where d is the separation between the plates. Find the expression for the capacitance when slab is inserted between the plates. C = 2C0K / (K+1)
Q.30 A capacitor of capacitance C1 is charged upto potential V volt and then connected in parallel to an uncharged capacitor of capacity C2. The final potential difference across each capacitor will be?? Ans. C1V/C1+C2
Q.31 A parallel plate capacitor of capacitance 90pF is connected to a battery of emf 20V. If a dielectric material of dielectric constant K = 5/3 is inserted between the plates, the magnitude of induced charge will be?? Ans. 1.2nC
Q.32 A 100 µF parallel plate capacitor having plate separation of 4mm is charged by 200 V DC. The source is now disconnected when the distance between plates is doubled and a dielectric slab of thickness 4mm and dielectric constant 5 is introduced between the plates. How will i) its capacitance, ii) the electric field between the plates and iii) electric density of a capacitor get affected ? justify your answer in each case. Ans. C’= 83.33 µF, E’= V’/2d, ue= 39825 x 10^-6 J/m^3
Comments
Post a Comment
If you have any doubts, let me know...