electric charges and fields neet questions || electric charges and fields jee questions

                     Dear students numericals of electric charges and fields neet questions and electric charges and fields jee questions aiims important questions have been collected at one place to get you all prepared for your neet, aiims ,jee main, advance exams as well as cbse board exams and other board exams. Visit my nawendu classes youtube channel for more help.
electric charges and fields neet numerical  questions
electric charges and fields

1. When ${{10}^{14}}$electron are removed from a neutral metal sphere ,the charge on the sphere becomes
Answer-16$\mu $C
2. How many electrons  will a body loss or gain to acquire -1C charge ?
Answer- $6.25\times {{10}^{18}}$ electrons will be gained.
3. What is the force between two small charged spheres having charges of 2 × ${{10}^{-7}}$ C and 3 × ${{10}^{-7}}$ C placed 30 cm apart in air?
Answer- 6x${{10}^{-3}}$N (Repulsive)
4. Two similar small spheres having +q and -q charge are kept at a certain distance. F force acts between the two. If in the middle of two spheres, an another similar small sphere having +q charge is kept, then it will experience a force in magnitude and direction as
Answer- 8F towards -q charge
5. Two spherical conductors B and C having equal radii and carrying equal charges on them repel each other with a force F when kept apart at some distance. A third spherical conductor having same radius as that B but uncharged is brought in contact with B, then brought in contact with C and  finally removed away from both. The new force of repulsion between B and C is 
       AIEEE 2004 
Answer- 3F/8
6. \[{{F}_{g}}\] and \[{{F}_{e}}\] represents gravitational and electrostatic force respectively between electrons Situated  at a distance 10cm. The ratio of $\frac{{{F}_{g}}}{{{F}_{e}}}$ is of the order of
Answer- ${{10}^{-42}}$
7. Two positive ions, each carrying a charge q. are separated by a distance d. If F is the force of repulsion between the ions, the number of electrons missing from each ion will be (e being the charge on an electron)
       CBSE AIPMT 2010 
Answer-  $\sqrt{\frac{4\pi {{\varepsilon }_{0}}F{{d}^{2}}}{{{e}^{2}}}}$  
9.    8. A charge Q is placed at each of the opposite corners of a square. A charge  is placed at each of the other two corners. If the net electric force on q is zero, then q/Q equals
       AIEEE 2009 
      Answer- -2√2
       9. Four charges equal to Q are placed at the four corners of a square and a charge q is at its centre . It the system is in equilibrium the value of q is
       AIEEE 2004 
       Answer- $\frac{Q}{4}\times (1+2\sqrt{2})$  
       10. Two point charges qA = 3 $\mu $C and qB = –3 $\mu $C are located 20 cm apart in vacuum.(a) What is the electric field at the midpoint O of the line AB joining the two charges?(b) If a negative test charge of magnitude 1.5 × ${{10}^{-9}}$ C is placed at this point, what is the force experienced by the test charge?
      Answer-(a)5.4x${{10}^{6}}$ N/C along OB  (b)8.1x${{10}^{-3}}$N along OA

11.Two point charges of + 5 x  ${{10}^{-19}}$C and + 20 x  ${{10}^{-19}}$C are separated by a distance of 2 m. Find the point on the line joining them at which electric field intensity is zero. 

 Answer- 2/3 m to the right of first charge
12. The point charge Q and -2Q are placed at some distance apart. If the electric field at the location of Q is E, the electric field at the location of -2Q will be
  AIIMS 2001 

Answer-  –E/2

13. A particle of mass m and charge q is placed at rest in a uniform electric field E and then released. The kinetic energy attained by the particle after moving a distance y is

       CBSE AIPMT 1998 

 Answer- qEy

14. There is an electric field ( E)  in X-direction. If the work done in moving a charge 0.2 C through a distance of 2m along a line making an angle 60 degree with   X-axis is 4J, the value of E is  

       AFMC 1998 
Answer- 20N/C
15. The mean free path of electrons in metal is 4 x ${{10}^{-8}}$m. The electric field which can give on an average 2eV energy to an electron in the metal will be in units of V/m
        CBSE- PMT 2009  
Answer- 5 x ${{10}^{7}}$ 
16. Calculate the electric field strength required just to support a water drop of mass ${{10}^{ -7}}$kg and having a charge 1.6 x ${{10}^{-19}}$C
      Answer- 6.125 x ${{10}^{12}}$N/C
      17. A charged oil drop is suspended in a uniform field of 3 x ${{10}^{4}}$ V/m so that it neither falls nor rise. The charge on the drop will be (Take mass of the charged drop = 9.9x${{10}^{-15}}$ kg and g=10 m/${{s}^{2}}$ )   
       AIEEE 2004 
Answer-   3.3 x${{10}^{-18}}$ C
18.A pendulum bob of mass 30.7 x ${{10}^{-6}}$kg and carrying a charge 2x${{10}^{-8}}$  C is at rest in a horizontal uniform electric field of 20000V/m. The tension in the thread of the pendulum is (g=9.8m/${{s}^{2}}$)    
       AIPMT  1990 
 Answer.-5 x ${{10}^{-4}}$ N
19. A conducting sphere of radius 10cm is charged with 10$\mu $C.Another uncharged sphere of radius 20cm is allowed to touch if for sometime. After that if the spheres are separated, then surface density of charge on the spheres will be in the ratio of   

       AIIMS 2002 

Answer- 2:1
20. Two spherical conductors A and B of radii 1mm and 2mm are separated by a distance of 5cm and are uniformly charged. If the spheres are connected  by the conducting wire then in equilibrium condition, the ratio of the magnitude of the electric field as the surfaces of the spheres A and B is
       CBSE AIPMT 1992,  AIEEE 2006  
Answer-   2:1
21. An oil drop of 12 excess electrons is held stationary under a constant electric field of 2.55 × ${{10}^{4}}$  N/C  (Millikan’s oil drop experiment). The density of the oil is 1.26 g ${{cm}^{-3}}$. Estimate the radius of the drop. (g = 9.81 m ${{s}^{-2}}$; e = 1.60 × ${{10}^{-19}}$ C).

22.An electric dipole, consisting of two opposite charges of  $2\times {{10}^{-6}}$ C each separated by a distance 3 cm is placed in an electric field of $2\times {{10}^{5}}$ N/C. Torque on the dipole is

       CBSE AIPMT 1995 

 Answer- $12\times {{10}^{-3}}$ N-m
23. An electric dipole consists of two opposite charges each of magnitude 1.0  $\mu $ C separated by distance of 2.0cm. The dipole is placed in an external field of 1.0 x ${{10}^{5}}$ N/C. The maximum torque on the dipole is
        CPMT -1990 
Answer- 2.0 x ${{10}^{-3}}$  N-M
24. An electric dipole is placed at an angle of 30 degree with an electric field intensity 2 x ${{10}^{5}}$ N/C.It experiences a torque equal to 4 Nm. The charge on the dipole ,if the dipole length is 2cm, is 
         NEET 2016 
 Answer.- 2mC

00. The potential at a point x (measured in $\mu $ m) due to some charges situated on  the x-axis is given by V(x) = 20/ (x2– 4) volt.The electric field E at x = 4 $\mu $ m is given  by

         AIEEE 2007  

Answer-  (10/9) V/$\mu $ m and in the  +ve   X direction


00. The electric potential V at any point x, y, z (all in metre) in space is given by  $V=4{{x}^{2}}$volt. The electric field at the point (1m, 0, 2 m) is ......... V/m

           IIT 1990, 1 M 

 Answer-  $-8\hat{i}$

00. The electric potential at a point ( x,y,z ) is given by  $V=-{{x}^{2}}y-x{{z}^{3}}+4$ .  The electric field  $\vec{E}$  at the point is

         CBSE AIPMT 2009 

 Answer-  $\vec{E}=\left( 2xy+{{z}^{3}} \right)\hat{i}+{{x}^{2}}\hat{j}+3x{{z}^{2}}\hat{k}$

 00. In a region ,the potential is represented by $V\left( x,y,z \right)=6x-8xy-8y+6yz$. Where V in volts and x,y,z are in meters. The electric force experienced by a charge of 2 C situated at point (1,1,1) is

          CBSE AIPMT 2014 

 Answer- $4\sqrt{35}$ N 
25. A  charge Q is enclosed by a Gaussian spherical surface of radius R. If the radius is doubled , then the outward electric flux will be
         CBSE AIPMT 2011 
 Answer.- Reamain the same
26. A hollow cylinder has a charge q within it. If $\varphi $ is the electric flux associated with the curved surface B, the flux linked with the plane surface A will be .
        AIIMS 2008 
A hollow cylinder

Answer.-$\frac{1}{2}(\frac{q}{{{\varepsilon }_{0}}}-\varphi )$
27.  A metallic solid sphere is placed in a uniform electric field . Which path is followed by the lines of force ?
         IIT 1996 

uniform electric field

Answer.-path 4 is correct
28.In air, the value of the total electric flux emitted from unit positive charge is
         AIIMS 2012 
 Answer.- $\varepsilon _{0}^{-1}$
29. A Square surface of side L metre in the plane of the paper is placed in a uniform electric field E(V/m) acting along the same place at an angle With the horizontal side of the square as shown in figure. The electric flux linked to the surface in unit of V-m, is

        CBSE AIPMT 2010 


A Square surface of side L

 Answer- 0

30. A square surface of side L meter is in the plane of the paper. A uniform electric field E ( V/m ), also in the plane of the paper, is limited only to the lower half of the square surface, (see figure). The electric flux in SI units associated with the surface is

      CBSE AIPMT 2006 


A square surface of side L meter

Answer- Zero

31. A charge q µC is placed at the centre of a cube of a side 0.1 m, then the electric flux diverging from each face of the cube is

      CBSE AIPMT 2001 

 Answer- $\frac{q\times {{10}^{-6}}}{6{{\varepsilon }_{0}}}$

 32. A charge Q $\mu $ C is placed at the center of a cube the flux coming out from any surface will be 

      AFMC 2001 

Answer- $\frac{Q}{6{{\varepsilon }_{0}}}\times {{10}^{6}}$ 

 33.A point charge +q is placed at mid-point of a cube of side L. The electric flux emerging from the cube is

     CBSE AIPMT 1996 

 Answer-  $\frac{q}{{{\varepsilon }_{0}}}$

34. A point charge of 2.0 $\mu $C is at the center of a cubic Gaussian surface 9.0 cm of edge. What is the net electric flux through the surface?

Answer- 1.9x${{10}^{5}}N{{m}^{2}}/C$

35. A charge q is placed at the corner of a cube of side a. The electric flux through the cube is

    CBSE AIPMT 2000 ,2012 

 Answer-  $\frac{q}{8{{\varepsilon }_{0}}}$

36. A point charge +10 µC is a distance 5 cm directly above the centre of a square of side 10 cm, as shown in Figure. What is the magnitude of the electric flux through the square? (Hint: Think of the square as one face of a cube with edge 10 cm.)

Answer- 2.2x${{10}^{5}}N{{m}^{2}}/C$
37. If the electric flux entering and leaving an enclosed surface respectively is  ${{\varphi }_{1}}$  and ${{\phi }_{2}}$ .The electric charge inside the surface will be                 
        AIEEE 2003 
Answer-  $({{\varphi }_{2}}-{{\varphi }_{1}}){{\varepsilon }_{0}}$

38. A hollow insulated conducting sphere is given a positive charge of 10 µC. What will be the electric field at the centre of the sphere if its radius is 2 m?

       CBSE AIPMT 1996 

Answer- Zero
39.The electric field in a certain region is acting radially outward and is given by E = Ar. A charge contained in a sphere of radius 'a' centred at the origin of the field' will be given by

      CBSE AIPMT 2015 

Answer-  $4\pi {{\varepsilon }_{0}}A{{a}^{3}}$

40.The electric field strength in air at NTP is  $3\times {{10}^{6}}$ V/m. The maximum charge that can be given to a spherical conductor of radius 3 m is

       CBSE AIPMT 1993 

 Answer-  $3\times {{10}^{-3}}$C
41. Two parallel large thin mental charge sheets have equal surface charge densities ($\sigma =26.4\times {{10}^{-12}}C/{{m}^{2}}$ ) of opposite signs. The electric field between these sheets ,is
        AIIMS 2006 
42.  A hollow charged conductor has a tiny hole cut into its surface. Show that the electric field in the hole is ($\sigma /2{{\varepsilon }_{0}}$ ) $\overset{\wedge }{\mathop{n}}\,$  , where $\overset{\wedge }{\mathop{n}}\,$ is the unit vector in the outward normal direction, and σ is the surface charge density near the hole.

# Assertion  and Reason
Direction -Read the Assertion and Reason carefully to mark the correct
Option from those given below
(a)Both Assertion and Reason are true and Reason is the correct explanation of
(b)Both Assertion and Reason are true but Reason is not the correct explanation of
(c)Assertion is true but Reason is false
(d)Both Assertion and Reason are false

43. Assertion –The electric  field due to a dipole on its axial line at a distance r is E.
Then, electric field due to the same dipole on the equatorial line and at the same distance will be E/2.
Reason- Electric field due to dipole varies inversely as the square of the distance.
 AIIMS 2017 
Answer- (C) Assertion is true but Reason is false
44. Assertion -A charge q is placed on a height h/4 above the centre of a square of side b. The flux associated with the square is independent of side length.
Reason – Gauss’s law is independent of the size of the Gaussian surface. 
 AIIMS 2015 
Answer- (A)Both Assertion and Reason are true and Reason is the correct explanation of Assertion
45. Assertion- A metallic shield in the form of a hollow shell may be build to block an electric
Reason- in a hollow spherical shield, the electric field inside it is zero at every point.              
 AIIMS 2012 
Answer- (A)Both Assertion and Reason are true and Reason is the correct explanation of Assertion
46. Assertion -A charged particle free to move in an electric field always moves along an
electric field line.
Reason -The electric field lines diverge from a negative charge and converge at a positive
charge .
      AIIMS 2009 
Answer-  (d)Both Assertion and Reason are false
47. Assertion -The coulomb force is the dominating force in the universe.
     Reason -The Coulomb force is weaker than the gravitational force. 
       AIIMS 2003 
Answer- (d)Both Assertion and Reason are false
48. Charge q is uniformly distributed over a thin half ring of radius R. The electric field at the center of the ring is.
     AIIMS 2009 
Answer- $\frac{q}{2{{\pi }^{2}}{{\varepsilon }_{0}}{{R}^{2}}}$

49. In a certain region of space, electric field is along the z-direction throughout. The magnitude of electric field is however not constant, but increases uniformly along the positive z-direction at the rate of ${{10}^{5}}$ $N{{C}^{-1}}{{m}^{-1}}$ . The force experienced by the system having a total dipole moment equal to ${{10}^{-7}}$ Cm in the negative z-direction is.   

     AIIMS 2015 
Answer- ${{10}^{-2}}$ N

50. 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 becomes

     NEET 2013 


pith balls

Answer-  $\frac{r}{\sqrt{2}}$   
51. 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 
      IIT 1987,2M ,CBSE AIPMT 1995
 Answer.-  -Q/4
52.Three charges +Q, q , +Q are placed respectively at distance 0, d/2 and d from the origin on the X-axis . if the net force experienced by +Q placed at x=o is zero , then
Value of q is
      IIT Main 2019, 9 jan shift 1 
 Answer.-  -Q/4
53. An electron of mass $\mathop{m}_{e}$ initially at rest ,moves through a certain distance in a uniform electric field in time $\mathop{t}_{1}$.A proton of mass $\mathop{m}_{p}$ ,also ,initially at rest ,takes time $\mathop{t}_{2}$ to move through an equal distance in this uniform electric field . Neglecting the effect of gravity , the ratio $\mathop{t}_{1}$ /$\mathop{t}_{2}$ is nearly equal to
      IIT 1997,1M 
 Answer.-  $\sqrt{{\mathop{m}_{p}}/{\mathop{m}_{e}}\;}$
54. Five point charges, each of value +q coulomb, are placed on five vertices of a regular hexagon of side L metre . The magnitude of the force on the point charge of value -q coulomb at the centre of the hexagon is ………..newton.

      IIT 1992, 1 M 


vertices of a regular hexagon

Answer- $\frac{1}{4\pi {{\varepsilon }_{0}}}.\frac{{{q}^{2}}}{{{L}^{2}}}$

55. Determine the electric dipole moment of the system of three charges, placed on the vertices of an equilateral triangle as shown in the figure.

     IIT Main 2019, 12 Jan I 


the system of three charges

Answer- $-\sqrt{3}ql\hat{j}$  

56. Obtain the formula for the electric field due to a long thin wire of uniform linear charge density E without using Gauss’s law. [Hint: Use Coulomb’s law directly and evaluate the necessary integral.] 

57. A charged wire is bent in the form of a semicircular arc of radius a. If charge per unit length is λ  coulomb/metre, the electric field at the centre O is

     CBSE AIPMT 2000 

Answer-  $\frac{\lambda }{2\pi {{\varepsilon }_{0}}a}$  

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