Charges Conductors & Coulomb's Law — Practice Questions

Free NEET Physics multiple-choice questions on Charges Conductors & Coulomb's Law. Attempt each question and reveal the answer with a full explanation.

A conductng sphere of radius R is given a charge Q . The electric potential and the electric field at the centre of the sphere respectively are: Q 4 πε 0 R , 0 0, Q 4 πε 0 R 2 Q 4 πε 0 R , Q 4 πε 0 R 2 0, 0 Two point charges -q and +q are placed at a distance of L , as shown in the figure. The magnitude of electric field intensity at a distance R(R >> L) varies as: 1 R 3 1 R 4 1 R 6 1 R 2 An electric dipole with dipole moment 5 10 -6 Cm is aligned with the direction of a uniform electric field of magnitude 4 10 5 N/C. The dipole is then rotated through an angle of 60 with respect to the electric field. The change in the potential energy of the dipole is: 1.5 J 0.8 J 1.0 J 1.2 J Two metal spheres of radii r 1 and r 2 are charged to the same potential. The ratio of their surface charge densities is: r 2 / r 1 r 1 / r 2 r 1 2 / r 2 2 1 : 1 Two point charges A and B , having charges +Q and -Q respectively, are placed at certain distance apart and force acting between them is F . If 25 % charge of A is transferred to B , then force between the charges becomes: 9F 16 F 16 F 4F 3 A charge q is placed at the center of a line joining two equal charges Q . The system of three charges will be in equilibrium if q is: -Q/4 -Q/2 +Q/2 +Q/4 Two point charges A and B , having charges +Q and -Q respectively, are placed at a certain distance apart and force acting between them is F . If 25 % charge of A is transferred to B , then the new force between them is: 9F 16 16F 9 4F 3 F Two identical metallic spheres A and B carry charges +Q and -2Q respectively. They are brought into contact and then separated by the same distance. The ratio of the initial force to the final force between them is: 8:1 4:1 2:1 1:1 A hollow metal sphere of radius R is uniformly charged. The electric field due to the sphere at a distance r from the center is: Zero as r increases for r < R , decreases as r increases for r > R Decreases as r increases for r < R and for r > R Increases as r increases for r < R and for r > R Zero as r increases for r < R , increases as r increases for r > R A point charge Q is placed at the center of an uncharged conducting spherical shell of inner radius a and outer radius b . The surface charge density on the inner and outer surfaces are respectively: -Q/(4 a 2), +Q/(4 b 2) +Q/(4 a 2), -Q/(4 b 2) -Q/(4 b 2), +Q/(4 a 2) 0, 0 A point charge +q is kept in the vicinity of an uncharged conducting plate. The force on the charge is: Attractive and perpendicular to the plate Repulsive and perpendicular to the plate Zero Parallel to the plate Two point charges q 1 = 2 C and q 2 = 1 C are placed at a distance of 2 m in air. The electrostatic potential energy of the system is: 9 10 -3 J 18 10 -3 J 4.5 10 -3 J 3 10 -3 J Twenty-seven drops of mercury, all of the same size, are charged to a potential of 10 V each. If they coalesce to form a single large drop, the potential of the large drop will be: 90 V 270 V 30 V 10 V Two point charges A and B , having charges +Q and -Q respectively, are placed at a certain distance apart and force acting between them is F . If 25 % charge of A is transferred to B , then the force between the charges becomes: 9F 16 15F 16 F 4F 5 Two metal spheres of radii 1 cm and 2 cm are given charges 10 -2 C and 5 10 -2 C respectively. If they are connected by a conducting wire, the final charge on the smaller sphere is: 2 10 -2 C 4 10 -2 C 1 10 -2 C 3 10 -2 C A charge q is placed at the center of the line joining two equal charges Q . The system of the three charges will be in equilibrium if q is equal to: -Q/4 Q/4 -Q/2 Q/2 The force between two charges 0.06 m apart is 5 N. If each charge is moved towards each other by 0.01 m, the new force will be: 11.25 N 6.25 N 2.25 N 20 N Two point charges +2 C and +6 C repel each other with a force of 12 N. If a charge of -4 C is given to each of them, the force will be: 4 N (attractive) 4 N (repulsive) 12 N (attractive) Zero Two point charges +3 μ C and +8 μ C repel each other with a force of 40 N . If a charge of -5 μ C is added to each of them, then the force between them will become: -10 N 10 N 20 N -20 N The electrostatic force between the metal plates of an isolated parallel plate capacitor C having a charge Q and area A is: Independent of the distance between the plates Linearly proportional to the distance between the plates Inversely proportional to the distance between the plates Proportional to the square root of the distance between the plates A charge Q is placed at the centre of the line joining two exactly equal positive charges q . The system of three charges will be in equilibrium if Q is equal to: -q/4 -q/2 q/2 q/4 Three point charges +q, -q and +q are placed at points (x = 0, y = a, z = 0) , (x = 0, y = 0, z = 0) and (x = a, y = 0, z = 0) respectively. The magnitude and direction of the electric dipole moment vector of this charge assembly are 2 qa along the line joining points (x = 0, y = 0, z = 0) and (x = a, y = a, z = 0) qa along the line joining points (x = 0, y = 0, z = 0) and (x = a, y = a, z = 0) 2 qa along +ve x direction 2 qa along +ve y direction A soap bubble is given a negative charge. Its radius will: Increase Decrease Remain unchanged Fluctuate A molecule of a substance has permanent dipole moment p . A mole of this substance is polarised by applying a strong electrostatic field E . The direction of the field is suddenly changed by an angle of 60 . If N is the Avogadro's number the amount of work done by the field is : 2NpE 1 2 NpE NpE 3 2 NpE A wheel having mass m has charges +q and -q on diametrically opposite points. It remains in equilibrium on a rough inclined plane in the presence of a vertical electric field E. Then value of E is : mg q mg q mg 2q mg 2q An electron falls from rest through a vertical distance h in a uniform and vertically upward directed electric field E . The direction of electric field is now reversed, keeping its magnitude the same. A proton is allowed to fall from rest in it through the same vertical distance h . The time of fall of the electron, in comparison to the time of fall of the proton is 10 times greater 5 times greater Smaller Equal Two point charges A and B, having charges +Q and - Q respectively, are placed at certain distance apart and force acting between them is F. If 25% charge of A is transferred to B, then force between the charges becomes : 4F 3 F 9F 16 16F 9 A dipole is placed in an electric field as shown. In which direction will it move? Towards the right as its potential energy will decrease. Towards the left as its potential energy will decrease. Towards the right as its potential energy will increase. Towards the left as its potential energy will increase. An electric dipole is placed at an angle of 30 with an electric field of intensity 2 10 5 N C -1 . It experiences a torque equal to 4 N m. Calculate the magnitude of charge on the dipole, if the dipole length is 2 cm. 8 mC 6 mC 4 mC 2 mC Two identical charged conducting spheres A and B have their centres separated by a certain distance. Charge on each sphere is q and the force of repulsion between them is F . A third identical uncharged conducting sphere is brought in contact with sphere A first and then with B and finally removed from both. New force of repulsion between spheres A and B (Radii of A and B are negligible compared to the distance of separation so that for calculating force between them they can be considered as point charges) is best given as: 3F 8 3F 5 2F 3 F 2 Which of the following statements are correct? A. Inside a conductor, the electrostatic field is zero. B. Electric field at the surface of a charged conductor does not depend on its surface charge density. C. The interior of a charged conductor can have no excess charge in the static situation. D. At the surface of a charged conductor, the electrostatic field must be normal to the surface at every point. E. The electrostatic potential is zero everywhere inside a charged conductor. Choose the correct answer from the options given below: A, C and D only A, C and E only C, D and E only A, B and D only Two metal spheres, one of radius R and the other of radius 2R respectively have the same surface charge density σ. They are brought in contact and separated. What will be the new surface charge densities on them? σ 1 = 5 6 σ , σ 2 = 5 12 σ σ 1 = 5 2 σ , σ 2 = 5 6 σ σ 1 = 5 3 σ , σ 2 = 5 6 σ σ 1 = σ , σ 2 = σ Two charges q and -3q are placed fixed on the x -axis separated by distance d . Where should a third charge 2q be placed such that it experiences no force? To the left of q at a distance d 3 -1 Between the charges To the right of -3q At the midpoint A charge Q is divided into two parts q and Q-q . What is the value of q for which the force between them is maximum? Q/2 Q/4 Q/3 3Q/4 A charge Q is placed at each of the two opposite corners of a square. A charge q is placed at each of the other two corners. If the net electrical force on Q is zero, then Q/q equals: -2 2 -1 1 -1/ 2 Two pith balls carrying equal charges are suspended from a common point by strings of equal length, the equilibrium separation between them is r . Now the strings are rigidly clamped at half the height. The equilibrium separation between the balls now become ( 1 2 ) 2 ( r [3] 2 ) ( 2r 3 ) ( 2r 3 ) Two identical charged spheres suspended from a common point by two massless strings of lengths l , are initially at a distance d (d << l) apart because of their mutual repulsion. The charges begin to leak from both the spheres at a constant rate. As a result, the spheres approach each other with a velocity v. Then v varies as a function of the distance x between the spheres, as : v x 1/2 v x v x -1/2 v x -1 If a charge q is moving in a circle of radius r around a charge Q at the center, the work done in one complete revolution is: Zero qQ / (4 0 r) qQ / (4 0 r 2) qQ / (2 0 r) A soap bubble is given a positive charge. Then its radius: increases decreases remains unchanged first increases then decreases Two parallel large thin metal sheets have equal but opposite surface charge densities . The electric field in the region between the sheets is: 0 2 0 2 0 Zero An electric dipole of moment p is lying along a uniform electric field E . The work done in rotating the dipole by 90 is:- 2 pE pE 2 2pE p E A spherical conductor of radius 10 cm has a charge of 3.2 10 -7 C distributed uniformly. What is the magnitude of electric field at a point 15 cm from the centre of the sphere? ( 1 4 0 =9 10 9 Nm 2/C 2 ) 1.28 10 5 N/C 1.28 10 6 N/C 1.28 10 7 N/C 1.28 10 4 N/C