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CBSE Important Questions

CBSE Guess > Papers > Important Questions > Class XII > 2011 > Physics > Physics By Mr. Ajay Sharma


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(Q.1) What is the direction of electric field intensity at a point on equatorial line of dipole? ( 1 mark )

(Q.2) Define electric dipole moment? ( 1 mark )

(Q.3) Define electric field intensity? ( 1 mark )

(Q.4) When does a dipole experiences maximum torque placed in uniform electric field? ( 1 mark )

(Q.5) What happens when an electric dipole is placed in non uniform electric field? ( 1 mark )

(Q.6) What is the value of electric field intensity inside a charged conductor? Why? ( 1 mark )

(Q.7) Explain, why two electric lines of forces cannot intersect each other. ( 1 mark )

(Q.8) How can we charge a body? ( 1 mark )

(Q.9) S1and S2are two parallel concentric spheres enclosing charges Q and 2 Q respectively as shown in Fig. The ratio of the electric flux through S1and S2 (H)

( 1 mark )

(a) 1/2
(b) 1/3
(c) 1/4
(d) 1/5

(Q.10) A charged particle having a charge of –3μC is placed close to a sheet of charge having a surface charge density 5×10–6C m–2.The force of attraction between the particle and the sheet of charge will be ( 1 mark )

(Q.11) Charges nC are seperated by 5 mm. The magnitude of dipole moment is ( 1 mark )

(Q.12) The value of charge on a body carrying 20 excess electrons is ( 1 mark )

(Q.13) The potential energy of two equal negative point charges 2 micro coulomb each, eld 1 meter apart in air is ( 1 mark )

(Q.14) The dielectric constant of a metal is ( 1 mark )

(Q.15) A charge of 2 coulomb moves between two plates maintained at a potential difference of 1 volt. The energy acquired by the charge is (H) ( 1 mark )

(Q.16) Dielectric constant of a medium is unity. Its permittivity will be ( 1 mark )

(a) 9.854 10-12 C2N-1m-2
(b) 8.254 10-12 C2N-1m-2
(c) 8.854 10-12 C2N-1m-2
(d) 6.854 10-12 C2N-1m-2

(Q.17) Two identical balls each have a mass of 10 g. What charges should these balls be given so that their interaction equalizes the gravitational force of attraction between them? The radii of the balls may be ignored in comparison to the distance between them. (H) ( 1 mark )

(Q.18) The S.I unit of surface integral of electric field is ( 1 mark )

(Q.19) An oil drop of 12 excess electrons is held stationary under a constant electric field of 2.55 ×104 V m –1in Millikan's oil drop experiment. The density of the oil is 1.26 g cm–3. Estimate the radius of the drop. Given that g = 9.81 m s–2and e = 1. 6 × 10–19 C. (H) ( 1 mark )

(Q.20) Calculate the total positive or negative charge on 3.11 g copper penny. Given Avogadro number = 6.02 × 1023 ,atomic number of copper=29 and atomic mass of copper = 63. (H) ( 1 mark )

(Q.21) A water particle of mass 10.0 mg and having a charge of 1.50 × 10–6C stays suspended in a room.The field will be ( 1 mark )

(Q.22) Electric field intensity due to a line charge is ( 1 mark )

(Q.23) There exists a non-uniform electric field along x-axis as shown in the figure below. The field increases at a uniform rate along +ve x-axis. A dipole is placed inside the field as shown. Which one of the following is correct for the dipole? (H) ( 1 mark )

(a) Dipole moves along positive x-axis and undergoes a clockwise rotation
(b) Dipole moves along negative x-axis and undergoes a clockwise rotation
(c) Dipole moves along positive x-axis and undergoes an anticlockwise rotation
(d) Dipole moves along negative x-axis and undergoes an anticlockwise rotation

(Q.24) The diagram shows the electric lines of forces emerging from a charged body. If the electric field at A and B are EAand EBrespectively and if the distance between A and B is r, then (H)( 1 mark )

(a) EA> EB
(b) EA= EB/r
(c) EA< EB
(d) EA= EB/r2

(Q.25) Two charges (+2 coulomb, –2 coulomb) are placed at a distance 0.5 m. Then their dipole moment will be : ( 1 mark )

(Q.26) Two charges (1 coulomb each) are placed at a distance 9 × 10–9m. Electric force between them will be ( 1 mark )

(Q.27) An electric dipole is kept in a uniform electric field. it experiences ( 1 mark )

(a) A force and a torque
(b) A force, but no torque
(c) A torque but no force
(d) Neither a force nor a torque

(Q.28) The dimensional formula for 0 is ( 1 mark )

(Q.29) Quantization of charge implies ( 1 mark )

(a) Charge cannot be destroyed
(b) Charge exists on particles
(c) There is a minimum permissible charge on a particle
(d) Charge, which is a fraction of a coulomb is not possible.

(Q.30) What happens when some charge is placed on a soap bubble? ( 1 mark )

(a) Its radius decreases
(b) Its radius increases
(c) The bubble collapses
(d) No effect is observed

(Q.31) Two spheres A and B of exactly same mass are given equal positive and negative charges respectively. Their masses after charging (H) ( 1 mark )

(a) Remain unaffected
(b) Mass of A > mass of B
(c) Mass of A < mass of B
(d) Nothing can be said

(Q.32) The distinction between conductors, insulators and semiconductor is largely concerned with ( 1 mark )

(a) Their ability to conduct current
(b) The type of crystal lattice
(c) Binding energy of their electrons
(d) Relative widths of their energy gaps

(Q.33) What is the dimentional formula for 0 ? ( 1 mark )

(a) M-2L1T-3A2
(b) M-1L-3T4A2
(c) M1L3T-4A-2
(d) M-3L-1T4A2

(Q.34) How many charges form 1 coulomb of charge? ( 1 mark )

(a) 6.25x1012
(b) 6.25x1016
(c) 0.625x1012
(d) 6.25x1018

(Q.35) What is the electric dipole moment of an electron and a proton 4 nm apart. ( 1 mark )

(a) 6.4x10-24 Cm
(b) 6.88x10-24 Cm
(c) 6.4x10-28 Cm
(d) 3.4x10-24 Cm

(Q.36) The potential difference between two points is 20 volt. How much work will be done in carrying charge of 400 μ C from one point to other? (H) ( 1 mark )

(a) 8x10-3 J
(b) 2x10-3 J
(c) 4x10-3 J
(d) 8x10+3 J

(Q.37) Define electric flux, also mention its formula? ( 2 Marks )

(Q.38) What will be the minimum electrostatic force between two charged particles placed at a distance of 1m apart? ( 2 Marks )

(Q.39) Define electric dipole moment. Give its direction? ( 2 Marks )

(Q.40) Define grounding or earthing? ( 2 Marks )

(Q.41) How is a neutral body electrified? ( 2 Marks )

(Q.42) What is a gold leaf electroscope? (H) ( 2 Marks )

(Q.43) An electric dipole, experiences a torque of 24x10-26 Nm. When it is placed 300 w.r.t a uniform electric field of strength 6x104 NC-1.calculate the dipole moment of the dipole? ( 3 Marks )

(Q.44) A dipole consisting of an electron and a proton separated by a distance 2x10-5m is situated in the electric field intensity of 4x105 NC-1 at an angle of 30 0 with the field. Calculate the dipole moment and the torque acting on it? (H) ( 3 Marks )

(Q.45) A solid sphere contains a uniformly distributed charge of density . What is the electric field inside the sphere at a distance r from the centre? ( 3 Marks )

(Q.46) A point charge is placed at the centre of a cube. What is the flux linked, (H)

(a) with the cube?
(b) with each face of the cube? ( 3 Marks )

(Q.47) Two point charges +9e and e are kept at distance x apart.At what distance a charge q should be placed from charge+e, so that q is in equilibrium. ( 3 Marks )

(Q.48) A system has two charges q = 2x10-7 C and q = -2x10-7 C located at points A(0,0,-10cm) and B(0,0,+10cm) respectively. find the total charge and electric dipole moment of the system. (H) ( 3 Marks )

(Q.49) State coulomb’s law, also derive the formula for the same. ( 3 Marks )

(Q.50) Mention some basic properties of electric charges? ( 3 Marks )

(Q.51) Write, in brief, the method to determine the distance of an inferior planet from the earth. ( 3 Marks )

(Q.52) “The magnetic lines of force prefer to pass through iron than air.” Give reason, ( 3 Marks )

(Q.53) Why is the energy of the electron emitted during beta decay continuous?(H) ( 3 Marks )

(Q.54) Give the equation for the charge density of continuous uniform charge distributions in the case of linear, surface and volume distribution of charges. (H) ( 5 Marks )

(Q.55) State Gauss law and derive the formula for electric field intensity of an infinite thin plane sheet of uniform surface charge density . ( 5 Marks )

(Q.56) Mention some important properties of electric field lines? ( 5 Marks )

(Q.57) Derive the formula for electric field of an electric dipole for the following two cases

(a) axial line (b) equatorial line. ( 5 Marks )


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