Title EXERCISE – 1 (Electrostatics).pdf ✅

1 ELECTROSTATICS EXERCISE–1: Basic Objective Questions Electric Charge and its Properties 1. A glass rod when rubbed with silk cloth acquires (a) +ve charge and silk cloth acquires equal –ve charge (b) No charge (c) –ve charge and silk cloth acquires equal +ve charge (d) +ve charge and silk cloth acquires more –ve charge Ans. (a) Sol. When a glass rod is rubbed with a silk cloth, electrons from the glass rod move to the silk cloth. During this process, the glass rod becomes positively charged and the silk cloth becomes negatively charged. Also, the magnitude of the charge on the silk cloth is the same as that on the glass rod. 2. Frictional electricity is produced on the two objects due to: (a) Loss of electrons by one object (b) Loss of protons by one object (c) Loss of electrons by one object and equal number of electrons gained by the other object (d) Loss of protons by one object and equal number of protons gained by the other object Ans. (c) Sol. Frictional electricity is also called as static electricity, which gets developed on objects when they are rubbed with each other. When rubbed with each other, both the objects get electrically charged where in one object acquires a positive charge due to loss of electrons from it whereas the other object acquires an equal negative charge due to gain of electrons by it. A glass rod rubbed with a silk cloth is an example of frictional electricity. 3. How many electrons will have a charge of one coulomb? (a) 6.25  1019 (b)6.25  1018 (c) 6.25  1015 (d) 1.6  10-19 Ans. (b) Sol. 19 e 19 19 18 Q 1.6 10 1e 1 1C e 1.6 10 1C 0.625 10 e 6.25 10 e − − − − − − =  =  =  =  =  4. A spherical conducting ball is suspended by a conducting thread. A positive point charge is moved near the ball. The ball will (a) be attracted to the point charge and swing towards it (b) be repelled from the point charge and swing away from it (c) not be affected by the point charge (d) either (a) or (b) Ans. (a) Sol. When a positive point charge comes closer to conducting ball, negative charges will be induced on the side of ball facing positive point charge. This process is also known as induction. Due to this induced opposite charge, there will be an attractive force between positive and negative charge. 5. When 1019electrons are removed from a neutral metal plate, the electric charge on it is (a) – 1.6 C (b) + 1.6 C (c) 19 10 C + (d) 19 10 C − Ans. (b) Sol. 19 19 Charge,q ne q 10 1.6 10 1.6C − =  =   = 6. For the phenomenon of electrostatic induction, mark out the correct statement. (a) The magnitude of the net induced charge is zero (b) The magnitude of net induced charge is equal and opposite to the inducing charge (c) The mass of the body changes slightly (d) Electrostatic induction is a permanent phenomenon Ans. (a)
ELECTROSTATICS 2 Sol. In the phenomenon of electrostatic induction, the magnitude of the net induced charge turns out to be zero because both the objects involved in the process develop opposite charges of equal magnitudes. 7. The specific charge of a proton is 9.6 × 107 C kg–1 . The specific charge of an alpha particle will be (a) 9.6 × 107 C kg–1 (b) 19.2 × 107 C kg–1 (c) 4.8 × 107 C kg–1 (d) 2.4 × 107 C kg–1 Ans. (c) Sol. Alpha particle is doubly ionized He atom. It carries a +ve charge, two times the charge of proton and mass of alpha particle is (2 Neutron + 2 Proton) almost 4 times the mass of proton. So, if specific charge of proton is p e m + = Then, specific charge of alpha particle p 2e 4m + = = Specific charge of proton  1 2 So, Specific charge of Alpha particle 7 9.6 10 7 1 4.8 10 Ckg 2  − = =  8. A comb rubbed through one’s dry hair attracts small bits of paper. This is because (a) comb is a good conductor (b) paper is a good conductor (c) the atoms in the paper get polarized by the charged comb (d) the comb possesses magnetic properties Ans. (c) Sol. When the comb passes through dry hair it gets electrically charged by friction. Hence, attracts small bits of paper. This is because paper gets polarized in the presence of charged comb resulting in a net force of attraction. 9. Assertion: When charges are shared between any two bodies, no charge is really lost, but some loss of energy does occur. Reason: Some energy disappears in the form of heat, sparking etc. (a) Both Assertion and Reason are true, and the Reason is the correct explanation of the Assertion. (b) Both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion. (c) Assertion is true, but Reason is false. (d) Both Assertion and Reason are false. Ans. (b) Sol. Charge is always conserved but energy is lost in the terms of heat etc. 10. Assertion: Charge is invariant. Reason: Charge does not depend on speed of frame of reference. (a) Both Assertion and Reason are true, and the Reason is the correct explanation of the Assertion. (b) Both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion. (c) Assertion is true, but Reason is false. (d) Both Assertion and Reason are false. Ans. (a) Sol. Any physical quantity which is independent of reference frame is known as invariant. Since charge is intrinsic property so it remains invariant. 11. Assertion: There is a spark or crackle when we take off our synthetic clothes or sweater in dry weather. Reason: Discharge of electric charges occurs through our body, which accumulated due to rubbing of insulating surface. (a) Both Assertion and Reason are true, and the Reason is the correct explanation of the Assertion. (b) Both Assertion and Reason are true, but the Reason is not the correct explanation of the Assertion. (c) Assertion is true, but Reason is false. (d) Both Assertion and Reason are false. Ans. (a)