Electrostatics. 4πε 2) + Q / 2 4) 4 Q

Transcription

1 Two spheres A and B of radius a and b respectively are at the same potential The ratio of the surface charge density of A to B is: ) a / b ) b / a a / b b / a Two free protons are separated by a distance of 0 A If they are released, the kinetic energy of each proton when at infinite separation is: ) x 0 9 J ) 5 x 0-9 J 46 x 0-9 J 56 x 0 - J A charge q is placed at the centre of the line joining of two equal charges each The system of three charges will be in equilibrium if q is equal to: ) / / 4 ) + / 4 4 A uniform wire of length 5m is carrying a steady current The electric field inside it is 0 V/m The potential difference across the ends of the wire is ) volt ) 05 volt 0 volt 5 volt 5 The electric potential due to an electric dipole at an axial point distant r from the dipole is related to r as: ) r ) r - r r - 6 A charge q is divided into two parts q and (q q ) What is the ratio q / q so that the force between the two parts placed a given distance apart is maximum? ) : ) : : :4 7 The electric potential at the surface of an atomic nucleus (Z=50) of radius 9 0 x 0 5 m : ) 80 volt ) 8 x 0 6 volt 9 volt 9 x 0 5 volt 8 Two point charges placed at a certain distance r in air exert a force of F on each other Then the distance r at which these charges will experience the same force in a medium of dielectric constant K is: ) r ) r / K r / K r K 9 An oil drop carrying a charge of 4 electrons has a mass of x 0-7 kg It is falling freely in air with terminal speed The electric field required to make the drop move upwards with the same speed is ( g = 0 m s ) ) x 0 V m - ) x0 V m - x 0 V m - 8 x 0 V m - 0 Six charges + each are placed at the corners of the regular hexagon of side a The electric field at the centre of hexagon is ) Zero 6 ) 0 a 0 a 6 0 a An isolated metal sphere of radius r is given a total charge q The potential energy of the sphere is: ) q / 4 π ε ) q / 4 π ε 9 r q / 8 π ε q / 8 π ε Charges +q, -4q and +q are arranged at the corners of an equilateral triangle of side 0 5 m If q = µ C ; their mutual potential energy is: ) 04 J ) 05 J 06 J 08 J Point charges 4 q, - q, + q and - q are placed at the corners of a square of side a The potential at point 0 ( the point of inter section of diagonals ) is: ) Zero 0 q ) 0q 0 5q 4 A bullet of mass g is moving with a speed of 0 ms - If the bullet has a charge of µc, through what potential must it be accelerated, starting from rest to acquire the same speed? ) 5 k V ) 5 V 50 V 50 k V 0

2 5 A hollow sphere of copper is having a uniform charge density of 05µC/m Its radius is 0m The potential at the centre of the sphere is: ) Zero ) 800 π volt 80 π volt 45 k V 6 An electron moving along positive x-axis with a speed of x 0 6 ms - enters the region of a uniform electric field The electron stops after traveling a distance of 90mm in the field The electric field strength is: (charge on electron = 6 x 0 9 C mass of electron = 9 x 0 - kg) ) 84 k V m -, along ve x - axis ) 0 84 k V m -, along ve x - axis 0 84 k V m -, along + ve x -axis 8 4 k V m -, along + ve x -axis 7 ABC is an equilateral triangle of side m Charges of + µc and - µc respectively are placed at points B and C The electric field at A is: ) 9 x 0 NC - ) 8 x 0 NC - 9 x 0 NC - parallel to BC 9 x 0 NC - parallel to CB 8 Two metal plates having a potential difference of 800V are cm apart It is found that a particle of mass 96 x 0-5 kg remain suspended in the region between the plates The charge on the particle must be (e = elementary charge): ) e ) 4 e 6 e 8 e 9 Total electric flux coming out of a unit positive charge put in air is: ) ε 0 ) ε 0 - (4 π ε 0 ) - 4 π ε 0 0 An electric dipole of moment p is placed normal to the lines of force of electric field E, then the work done in deflecting it through an angle of 80 degrees is: ) p E ) + p E - p E Zero The ratio of momentum of an electron and an alpha particle which are accelerated from rest by a potential difference of 00V is: ) m ) e m α m α m e m e mα A region surrounding a stationary electric dipole has: ) Magnetic field only ) Electric field only Both electric and magnetic fields No electric and magnetic fields Two pith balls each of mass m and charge q are suspended from a point by weightless threads of length l Both the threads are separated by an angle θ with the vertical If the value of θ is negligible, the distance between two pith balls will be ) q l 0mg ql 4 0mg ) q l 4 0mg ql 0mg 4 The dielectric constant K of an insulator cannot be: ) 4 ) When the distance between two charged particles is halved, the coulomb force between them becomes: ) one-half ) one-fourth double four times 6 The minimum charge on an object is ) One coulomb ) One stat coulomb 6 x 0-0 coulomb 6 x 0-9 coulomb

3 7 Two charges q and q are placed in vacuum at a distance d, and the force acting between them is F If a medium of dielectric constant 4 is introduced around them, the force now will be: ) 4 F ) F F F 4 8 A solid metallic sphere has a charge + Concentric with this sphere is a conducting spherical shell having charge The radius of the sphere is a and that of the spherical shell is b (b>a) What is the electric field at a distance R (a < R < b) from the centre? ) ) πε 0 R πε 0 R 4 πε 0 R 4 πε 0 R 9 In a region of space having an uniform electric field E, a hemi-spherical bowl of radius r is placed The electric flux φ through the bowl is: ) πr E ) πr E πre 4πr E 0 A hollow spherical conductor of radius m carries a charge of 500µC Then the electric field strength at its surface is: ) Zero ) 5 x 0 6 N/C 5 x 0 6 N / C 4 5 x 0 6 N / C The electric field intensity on the surface of a charged conductor is: ) Zero ) Directed normally to the surface Directed tangentially to the surface Directed along 45º to the surface A proton is released from rest at a distance of 0-4 A 0 from the nucleus of a mercury atom (Z=80) The kinetic energy of the proton when it is far away from the nucleus is: ) e V ) k e V M e V M e V Two thin concentric hollow conducting spheres of radii R and R bears charges and respectively If R > R, then the potential at a point distant r such that: R > r > R is ) + ) 0 r 0 r R 0 R R 0 R r 4 Two thin concentric hollow conducting spheres of radii R and R bears charges and respectively If R > R, then the electric field strength at a point distant r such that R > r > R is: ) Zero ) + 5 Two small spheres carry charge of + n C and n C respectively The charges are distance d apart The force they exert on one another is F The spheres are made to touch one another and then separated to distance d apart The force they exert on one another now is F Then F / F is: ) ) / 6 : 9 6 A cylinder of radius R and length L is placed in the region of a uniform electric field E such that its axis is along the direction of electric field The electric flux linked with cylinder is: ) R/L ) R /L Zero Infinity 7 Two metallic spheres of radii cm and cm are given charges 0 - C and 5x0 - C respectively If they are connected by a conducting wire, the final charge on the smaller sphere is: ) x 0 - C ) x 0 - C 4 x 0 - C x 0 - C

4 4 8 If the dielectric constant and dielectric strength be denoted by K and X respectively, then a material suitable for use as a dielectric in a capacitor must have ) high K and high X ) high K and low X low K and high X low K and low X 9 An electric dipole consists of two opposite charges each of magnitude 6x0-9 coulomb at separation 0 A The dipole moment is: ) 6 x 0-9 coul-metre ) 6 x 0-9 coul-metre x 0-9 coul-metre 0 8 x 0-9 coul-metre 40 A is a spherical conductor placed concentrically inside a hollow spherical conductor B + charge is given to A and B is earthed The electric intensity is not zero ) inside A ) outside B on the surface of B between A and B 4 Electron and proton are accelerated from rest by a potential of V volt Mass of proton is 840 times the mass of electron v e, K e and K p, stand for the speed and kinetic energy of electron and proton respectively Then: ) v e = v p ; K e = K p ) v e < v p ; K e < K p v e < v p ; K e > K p v e > v p ; K e = K p 4 The work done in carrying a charge of 5 µc from a point A to B is 8mJ The difference of potential between A and B is: ) 60 V ) 6 V 6 k V 6 k V 4 Compare electrons accelerated through a certain potential difference and protons accelerated through the same pd If initial velocities are negligible, then the emergent; ) electrons have smaller kinetic energy ) protons have larger velocity electrons have larger momentum protons have larger momentum 44 The fact that electric charges are integral multiples of the fundamental electronic charge was proved experimentally by: ) Planck ) JJ Thomson Einstein Millikan 45 An electron enters with a velocity of 5x0 6 m/sec along the positive direction of an electric field of intensity 0 newton per coulomb If mass of electron is 9 x 0 - kg, then the time taken by the electron to come temporarily to rest, is: ) 5 8 x 0-8 sec ) 45 x 0-8 sec 9 x 0-8 sec 46 There are 7 drops of a conducting fluid Each has a radius a and they are charged to a potential V 0 These are combined to form a bigger drop Its potential will be: ) V 0 ) V 0 9 V 0 7 V 0 47 A particle having a charge 0x0-9 coulomb experiences a downward force of 5x0-6 newton when placed in a field of electric intensity (in Newton per coulomb), is: ) 5 x 0 horizontally ) 5 x 0 vertically downward 5 x 0 vertically upward 5 x 0-5 vertically upward 48 Charges of + ( 0 / ) x 0 9 C are placed at each of the four corners of a square of side 8 cm The potential at the intersection of the diagonals is: ) 50 volt ) 500 volt 900 volt d) 900 volt 49 An electron placed at a distance of 05m from a charge placed at origin, experiences a force of 9 6 x 0-6 N along positive x - axis The electric field at the position of electron is: ) 6 x 0 NC - along + ve x - axis ) 6 x 0 NC - along ve x - axis 5 6 x 0-4 NC - along + ve x - axis 5 6 x 0-4 NC - along ve x - axis

5 5 50 A rectangle of cross-sectional area A is placed in a uniform electric field The normal to the area of the coil makes an angle of 90º with the electric field The electric flux, φ, through the rectangle is: ) E ) A E A E / Zero 5 The number of electric lines of force crossing the surface of an arbitrary curve of surface area S and enclosing a charge q is: ) 0 ) q 0 S q / 0 q V / 0 Where q is the charge inside the closed surface 5 Equal charges q are placed at the four corners A, B, C, D of a square of length a The magnitude of the force on the charge at D will be: q 4q ) ) 0a 0a + q q + 0a 0a 5 Two charges are 40µC and -0µC They are some distance apart Now they are touched and kept at the same distance The ratio of the initial to the final force between them is: ) 8 : ) 4 : : 8 : 54 Charges of µc and -µc are placed respectively at two points A and B distant m The distance of the point from A, where net potential is zero, is: ) m ) 0 5 m 0 4 m 0 6 m 55 Charges q and q are placed respectively at points A and B The net force on a unit positive charge placed at a distance of: 56 Electric potential V at some point in space is zero This means: ) Electric field at that point is necessarily zero ) Electric field at that point is necessarily non-zero Electric field at that point may or may not be non-zero The point is on the surface 57 Equal charges q are placed at the three corners A, B & C of a square ABCD of side a The potential at A is: ) q q ) 0 a 0 a q q + πε [ + 4 0a 0a ] 58 Equal charges q are placed at the three corners A, B & C of a square ABCD of side a The ratio of potential at A and O (the point of intersection of diagonals) is: ) ) An electric dipole consists of two opposite charges each of magnitude 0 µ C separated by a distance of 0 cm The dipole is placed in an external field of 0 x 0 5 N / C The maximum torque on the dipole is: )0 x 0 - N- m ) 0 x 0 - N-m 0 x 0 - N- m 4 0 x 0 - N-m 60 Charges +q, -q, +q and q are placed at the corners A, B, C & D of a square ABCD of side a The charge A is in equilibrium The ratio q /q is: ) ) / ) 0 6 m ) (- + ) / m ( - - ) / m 05 m from A is zero