Electric Field and Potential Questions and Answers

Two spheres A and B of same mass M are given equal positive and negative charges Q and Q respectively Their masses after charging 1 Remains same 2 Mass of sphere A mass of sphere B 3 Mass of sphere A mass of sphere B 4 Cannot be predicted

4 A wire of length is bent to form a semicircle If it has charge Q then electric field intensity at the centre of the ring is a Qn 4801 b Q c 4 1 O O 480 2801 d

If identical charges q are placed at each corner of a cube of side b then electric potential energy of charge q which is placed at centre of the cube will be 1 2 8 2q 4 eob 3 8 2q TEOb 4 2q TEOb 40

An oil drop of mass 50 mg and of charge 5 C is just balanced in air against the force of gravity Calculate the strength of the electric field required to balance it g 9 8 ms 2 a 98 NC upwards b 98 NC downwards c 9 8 NC towards north d 9 8 NC towards south

32 a Consider an arbitrary electrostatic field configuration A small test charge is placed at a null point i e where E 0 of the configuration Show that the equilibrium of the test charge is necessarily unstable b Verify this result for the simple configuration of two charges of the same magnitude and sign placed a certain distance apart

A spherical body P has a positive charge on it attracts an another sphere Q placed near it Th sphere Qis 1 Negatively charged 2 Positively charged 3 Neutral 4 May be negative or neutral

Two charges q and 4q are kept at a separation d Another charge Q is placed on the line joining the two charges such that all the three charges are in equilibrium Find the value of charge Q and its location ion Fig 1 13 shows two charges q and 4q respectively at A F Q F q 4q

5 A system consists of two concentric conducting spheres with the inside sphere of radius a carrying a positive charge q What charge 92 has to be deposited on the outside sphere of radius b to reduce the potential of the inside sphere to zero How does the potential depend in this case on a distance r from the centre of the system Draw the approximate plot of this dependence 6 Four large metal plates are located at

field intensity is zero 2 m Find the point C B S E 01 Ans 2 3 m 78 Two positive charges of 10 C each are situated 10 x 10 2 m apart from each other What is the increase in the electrostatic potential energy of the system when the two charges are brought closer by 2x 10 2 m Express your answer in S I unit Ans 2 25 J 79 An electric dipole of length 2 x 10 m is placed with A

40 An electric dipole consists of two point charges 4 C and 4 C placed 24 cm apart Find the electric potential at a point lying 4 x 10 2 m away from the centre of the dipole a on the dipole axis and b on the perpendicular bisector of the dipole c Determine also the electric potential at the point lying 20 x 10 2 m away from its mid point at an angle 60 with the dipole axis d What will be its minimum and maximum potential energy when placed in an electric field of intensity 2 x 105 V m Ans a 4 8 x 105 V b 0 c 0 9 V d 16 x 10 2 J 16 x 10 2 Jl

0 A uniformly charged solid sphere of radius R has potential Vo measured with respect to o on its surface For this sphere the equipotential surfaces with potentials 3V0 5V 3Vo 24 4 and have radius R R R3 and R4 respectively Then Vo 4 a R 0 and R R4 R3 b 2R R

1 A charged particle of mass m and charge q is released from rest from position x 0 0 in a uniform electric field Eoj The angular momentum of the particle about origin a is zero c increases with time b is constant d decreases with time

5 How many electrons may be removed from a body so that it may have a charge of a 1 milli coulomb b 1 micro coulomb h 6 25 x 1012 electrons

Example 1 2 If 10 electrons move out of a body to another body every second how much time is required to get a total charge of 1 C on the other body 3 Therefore 01 C t C

Example 1 3 How much positive and negative charge is there in a cup of water

a Example 1 13 An early model for an atom considered it to have positively charged point nucleus of charge Ze surrounded by a uniform density of negative charge up to a radius R The atom as a whole is neutral For this model what is the electric field at a distance r from the nucleus R P

A positive point charge qo is placed t a point C inside the cavity in spherical conductor as shown in figure Find the electric potential at point P Given K 1 Kqo 2a 2Kq 1 41E0 P a 2 C 7th 2a 2 4 Kqo a L 3Kqo

Tom Screen pus It implies that the field at every point on a circle of radius r with the wire along the axis is same in magnitude In other words the magnetic field possesses what is called a cylindrical symmetry The field that normally can depend on three coordinates depends only on one r Whenever there is symmetry the solutions simplify

Find the force on the charge q in the Figure shown below The zy plane is a grounded conductor Xx 3d q de 2q y V 0

The plane x 0 is uniformly charged with the surface density o 0 and the plane y 0 with the surface density o Find the strength of the electric field in space and sketch the course of the field line

Two charges 9 c and 9 c are placed at the points P 1 0 4 m and Q 2 1 5 m located in the electric field E 0 201 the dipole O 25 x 10 7N m O 25 x 10 5 N m O 15 x 10 7N m O 15 x 10 5 N m V cm Calculate torque acting on 4

Q13 Two point like objects each carrying charge 10Q are separated by a distance d The force between them is F If half the charge on one object is transferred to the other object while at the same time the distance between them is doubled what is the new force between the two objects O A 0 25 F O B 4 0 F O C no change in F D 0 19 F

What is angle between equipotential surface and electric field Write equation for potential energy of electrical dipole in vector form Define dielectric constant in terms of capacitance What is formula for capacitance of parallel plate capacitor What are factors on which capacitance of parallel plate air capacitor depends Which combination should be used to increase equivalent capacitance Dielectric constant of a medium is 5 find relative permittivity of the medium A capacitor of 2uF is charge up to 200 volts What is energy stored in it Two capacitors of same capacitance give equivalent capacitance C 2 in series What valent capacitance in parallel Charges q and 2q are enclosed by a surface What is total flux passing from the surface Charges each q are kept at points a 0 and 0 a find electric fields at origin If intensity of electric field in axial position is E what would be electric field at this point if dipc uatorial position

Q 9 A point positive charge is brought near an isola conducting sphere in Figure The electric field is best given by 30 i ii E iv 9 9 MOJA 9 A Fig i C Fig ii Ans Option B is correct B Fig iii D Fig iv 99 A Explanation As given charge is q and lines of forces in positive charge must be outwards from positive charge q Now as the positive charge is kept near an isolated conducting sphere due to induction left part of sphere gets accumulated negative charge and right part gets positive and lines of force from right part of sphere must emerge outwards normally So verifies the answer B As lines of fo

PHYSICS AB and CD are two uniform resistance wires of lengths 100 cm and 80 cm respectively The connections are shown in the figure The cell of emf 5 V is ideal while the other cell of emf E has internal resistance 2 2 A length of 20 cm of wire CD is balanced by 40 cm of wire AB Find the em E in volt if the reading of the ideal ammeter is 2 A The other connecting wires have negligibl resistance AL Ca 5V 41 40 cm 20 cm www F 2 0 B D A Ammeter ideal

19 An infinitely long wire is kept along z axis from z to z having uniform linear charge 10 density nc m The electric field at point 6 cm 8 cm 10 cm will be nc 1 120i 160j 200k V m 3 160i 120j v m K X 2 200k V m 4 120i 160j V m Ans A

or NEET Part 1 poles identical in nature are arranged 19 In the arrangement of concentric she below Find net electric field Q 2 2kP the given figure the ratio of electric field at poir 1 2 is 1 1 2 3 4 3 2R Q2r 3R 2Q 3Q 2 3 4 4 2 3 20 A charged particle of mass m 1 kg and charge horizontal ground at an

2 2 Initial charges with proper sign on the plates of two identical capacitors each of 1 F are as shown When both and S are closed the potential difference between A and B will S finally become A 2V R C 6V S A 2 C 4 C 6 C 12 C 6 CIF Figure 2 236 B 4V D OV S B

If the potential difference of Coolidge tube producing X ray is increased then choose the correct option s The interval between Aka and Akp increases The interval between Aka and increases increases The interval between Akp and o does not change Here is cutoff wavelength and ka and Akp are wavelength of a and 2 characteristic X rays

Is it possible that any battery has some constant non zero value of emf but the potential difference between the plates is zero 1 Not possible 2 Yes if another identical battery is joined in series 3 Yes if another identical battery is joined in opposition 4 Yes possible if another similar battery is

from the wire Pick out the WRONG statement 1 The gain in the K E of the electron moving at right angles to the magnetic field is zero 2 When an electron is shot at right angles to the electric field it traces a parabolic path 3 An electron moving in the direction of the electric field gains K E 4 An electron at rest experiences no force in uniform and constant the magnetic field

charge d 4F towards charge A cylinder of radius R and length L is placed in a uniform electric field E parallel to the cylinder axis The total flux for the surface of the cylinder is given by a 2 R E c TR TR b Nab Zero

A proton and an electron are held apart a distance of 1 m and then let go Where would they meet O E P a in the middle b closer to the electron s side c closer to the proton s side

9 A force F acts between two charges Q and Q that is placed at a certain distance from eac other The third sphere of charge Q is placed between them What is the magnitude and force experienced by the third charge A 3F in the direction of Q charge B 4F in the direction of Q charge C 8F in the direction of Q charge D No direction and magnitude is zero

A conducting bar of length L is free to slide on two parallel conducting rails as shown in the figure R Two resistors R and R are connected across the ends of the rails There is a uniform magnetic field B pointing into the page An external agent pulls the bar to the left at a constant speed V R The correct statement about the directions of induced currents I and I2 flowing through R and R respectively is A Both I and 12 are in clockwise direction B I is in clockwise direction and I2 is in anticlockwise direction I is in anticlockwise direction and I is

wo poin the circumference of a uniform conducting ring of radius r and resistance R Arc AB of the ring subtends an angle 0 at the centre The value of the magnetic induction at the centre due to the current in the ring is Resita R R 360 6 21 20 215 P A 1 zero only if 0 180 2 zero for all values of 0 3 proportional to 2 180 0 B 36 1 362 BE

Charge Q coulomb s is uniformly distributed throughout the volume of a solid non conducting hemisphere of radius R then potential at its centre is 1 2 3 fo 1 Q 4meo 4R 1Q 41 R 1 3Q 420 2R 1 3Q

Two balls with charges Q and 4Q are separated by 3R Where should you place another charged ball Q on the line between the two charges such that the net force on Q will be zero e Od 9 b R 3R d 2R 4Q

Spherical shell A is made up of insulating material and carries electric charge uniformly distributed over its surface while Spherical shell B is made up of conducting material and carries no charge C and C are centres of Shell A and Shell B respectively Choose the correct statement 1 2 3 4 Shell A Question Type Single Correct Type Shell B electric field at centre C of shell B due to charge of shell A is zero electric field at centre C of shell B due to induced charges on surface of shell B is zero direction of electric field at point A on shell B due to induced charges on surface of shell B is radial direction of electric field at point P on shell B due to induced charges on surface of shell B is radial

You have two coaxial cylindrical conducting shells one with radius a and the second radius b a b The inner shell radius a is at potential V 0 the outer shell radius b is held at potential Vo Find the potential V r everywhere assuming the cylinders are infinitely long b V 0 O

1 23 points An electron has an initial speed of 6 2 x 106 m s at point A The electron moves from point A and stops at point B Find the potential difference VA VB between the two points in volts

Two large parallel sheets charged uniformly with surface charge density o and o located as shown in the figure Which one of the following graphs shows the variation of electric field along a line perpendicular to the sheets as one moves from A to B A B 0 AX 0 be X B

A point charge of 40 stat coulomb is placed 2 cm in front of an earthed metallic plane plate of large size Then the force of attraction on the point charge is 1600 dynes 160 dynes 400 dynes Incorrect Correct

When current changes from 2 A to 2 A in 0 05 s an emf of 8 V is induced in a coil Co efficient of self induction of coil is 1 0 2 H 3 0 8 H NG 2 0 4 H 4 0 1 H

O No 24 A thin metal shell enclosed by concentric thick hollow metal sphere then potential at point P is 20 1 2 3 KQ C KQ a KQ C zoro KQ KQ 2KQ

5 A uniformly charged solid sphere of radius R has potential Vo measured with respect to on its Vo surface For this sphere the equipotential surfaces with potentials 3V 5V 3Vo 4 and 17 have 4 2 4 radius R R R and R4 respectively Then 1 R 0 and R R4 R 3 R 0 and R R4 R 2 R 0 and R R R4 R 4 2R R

A charge Q is placed at origin The electric potential due to this charge at a pointi space is V The work required by external agent force to bring a charge qo from infinity to that point is Vqo Va 2 10

6 9Q An electric dipole is placed at origin with its dipole moment directed along negative x axis The direction of electric field at point 1 2 0 is 1 Along positive y axis 2 Along positive x axis 3 Along negative x axis 4 Along negative y axis

Two spherical conductors of radii 4 cm and 5 cm are charged to same potential I 0 and 0 be respective charge densities of charges on both conductors then ratic of 1 is 04 5 05 4 25 16

If E represents the electric field at point A and V represents the potential at point A due to a small dipole p as shown in the diagram then which of the following relation is incorrect K E V Kp F VA E 3 p F 6 tana tane 2 kn 1 4180