Electric Charges and Fields

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Electric Charges and Fields

Consider 3 charged bodies P,Q ,R
Consider 3 charged bodies P,Q ,R . If P & Q repel each other and P &R attracts, what is the nature of force b/w Q&R ? Ans. Attractive, because Q & R will carry opposite charges. 2) Why does an ebonite rod acquires –vely charged on rubbing with fur? Ans. This is because electrons in the fur are less tightly bound than electrons in ebonite rod.

(i) which particle will experience a force of larger magnitude?
3) An electron and a proton moving with same uniform velocity v enter a uniform mag. Field (i) which particle will experience a force of larger magnitude? (ii) which particle will have an acceleration of larger magnitude? Ans. (i) The mag. Of the electric force is F=qe . For electron and proton, q is the same. Hence both experienceforce of same magnitude. (ii)acceleration, a = Force mass i.e. a is inversly proportional to mass when force is same. Since mass of electron << mass of proton, acceleration of electron will be very much larger than that of proton. (HOTS)

4)Why electrostatics is also known as frictional electricity. Ans
4)Why electrostatics is also known as frictional electricity? Ans. Charges at rest are produced due to friction b/w 2 insulating bodies ,which are rubbed against each other. Hence electrostatics is also known as frictional electricity. 5)What common name can be given to electron, proton and neutron? ans. They are called elementary particles.

5)Who proved that like charges repel and unlike charges attract. Ans
5)Who proved that like charges repel and unlike charges attract? Ans. Dr. William Gilbert proved that like charges repel and unlike charges attract. 6)Name c.g.s and SI units of charge. Ans. The c.g.s units of charge is 1 stat coulomb or 1 e.s.u of charge. SI unit of charge is 1 coulomb.

7) Two point charges of unknown magnitude and sign are placed at a distance d apart, the electric field intensity is zero at a point not b/w the charges but on the line joining them. Write 2 essential condition for this to happen. Ans. (i) the 2 point charge should be of opposite signs. (ii) the magnitude of the charge nearer the point under consideration should be smaller than the magnitude of the other charge. (HOTS)

8)Why can one ignore quantization of electric charge when dealing with large scale charges? Ans. Variation in the quantity of charge by a few electrons does not get noticed for large scale charges as the charge on an electron is very small. 9)Does motion of a body affects its charge ? Ans. No, charge on the body does not change with motion of a body .

10)How many electrons make up one coulomb of –ve charge. Ans
10)How many electrons make up one coulomb of –ve charge ? Ans. from , q=ne, n= qle = = 11)What is the cause of charging? Ans. The cause of charging is actual transfer of electros from one body to the other. 12)An isolated conducting sphere is given a +ve charge. Does its mass increase, decrease or remain the same? Ans. Its mass decreases slightly as it looses some electrons.

13)An ebonite rod is rubbed with fur or wool
13)An ebonite rod is rubbed with fur or wool. What type of charge do they acquire? Ans. The ebonite rod acquires –ve charge and the fur acquires equal +ve charge. 14) Is the coulomb force that one charge exerts on another changes if other charges are brought nearby? Ans. No, the coulomb force due to one charge is not changed. 15) Can ever photon have a charge ? If not why? Ans. no, photons can never have a charge. This is because charge cant exist without rest mass.

17)How does a free electron at rest move in an electric field. Ans
17)How does a free electron at rest move in an electric field? Ans. a free electron at rest move in a direction opp. to electric field. 18)Name any 4 vector fields? Ans. Electric field ,magnetic field ,gravitational field and flow field(of a liquid). 19)Why is electric field intensity inside a charged conductor zero? Ans. This is because there is no electric lines of force inside the body of a conductor.

20)how does a torque affect the dipole in an electric field. Ans
20)how does a torque affect the dipole in an electric field? Ans. Torque tries to allign the dipole along the field. 21) Two point charges of +3µC each are 100cm apart. At what point on the line joining the charges will the electric intensity be zero? Ans. At the centre. 22)What is the nature of symmetry of dipole field? ANS. the field due to dipole has a cylindrical symmetry.

25) At what points, dipole field intensity is parallel to the line joining the charges? Ans. At any point on axial line or equatorial line of dipole. 26) Do electrons tend to go to regions of high potential or low potential? Ans.as electrons are –vely charged , they have a tendency to go to regions of high potential. 27) No work is done in moving a test charge over an equipotential surface . Why ? Ans. W=Charge× pot. diff. = zero

28)Name the expt., which established that electric charge has quantum nature. Ans. Millikan’s oil drop expt. 29)What do you understand by the principle of superposition of charge? Ans. It states that the total electrostatic force on a given charge is the vector sum of the individual forces exerted on it by all other charges. 30)How does the force b/w 2 point charges change if the dielectric constant of the medium in which they are kept increasing? Ans. force b/w them decrease on increasing the dielectric constant of the medium b/w them as F inversily proportional to K, K being dielectric constant.

31)Can a body have a charge of 0. 8×10⁻¹⁹C
31)Can a body have a charge of 0.8×10⁻¹⁹C. Justify your ans by a comment? Ans. No, a body can’t have fractional charge of an electron. (q=±ne, n=integer) 32) How many electrons are contained in 1µC? Ans. q=ne 1µC= n×1.6× 10 ⁻¹⁹C therefore, n= 10 ⁻⁶C = 6.25×10¹² 1.6×10 ⁻¹⁹C

33) Ordinary rubber is an insulator ,but the special rubber tyres of aircrafts are made slightly conducting. Why is this necessary? Ans. During landing the tyres of aircraft gets charged due to friction b/w tyres and ground ,in case, the tyres are slightly conducting, the charge developed on the tyres will not stay on them and it finds its way to the earth.

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