This mcq (multiple choice question ) is most important for exam neet 2020 and jee mains 2020 and jee advanced 2020 .
This test is gives us basic knowledge of charge means electrostatics charge .
These question and theory is very good for cbse 12th physics as well as neet /jee/jee mains /jee advanced /neet abhyas test 2020
Electrostatics notes -1
Charge
(1) Charge is the property associated with matter due to which it produces and experiences electrical and magnetic effects.
(2) It is known that every atom is electrically neutral, containing as many electrons as the number of protons in the
nucleus.
(3) Charged particles can be created by disturbing neutrality of an atom. Loss of electrons gives positive charge (as then
np>ne) and gain of electrons gives negative charge (as then ne>np) to a particle. In charging mass of the body changes as
shown below
(4) Charges with the same electrical sign repel each other, and charges with opposite electrical sign attract each other.
(5) Charge is
Transferable : It can be transferred from one body to another
Associated with mass : Charge cannot exist without mass but reverse is not true.
Conserved : It can neither be created nor be destroyed.
Invariant : Independent of velocity of charged particle.
(6) Electric charge produces electric field , magnetic field and electromagnetic radiations.
(7) Charge on a conductor : Charge given to a conductor always resides on it's outer surface.This is why a solid and
hollow conducting sphere of same outer radius will hold maximum equal charge.If surface is uniform the charge
distributes uniformly on the surface and for irregular surface the distribution of charge, i.e., charge density is not
uniform. It is maximum where the radius of curvature is minimum and vice versa. i.e., . This is why charge leaks
from sharp points
.
(8) Quantization of charge : If the charge of an electron () is taken as elementary unit i.e. quanta of
charge, the charge on any body will be some integral multiple of ei.e.,
with
Charge on a body can never be , ±17.2e or ±10–5eetc.
Methods of ChargingA body can be charged by following methods.
By friction : By rubbing two bodies together, both positive and negative charges in equal amounts appear
simultaneously due to transfer of electrons from one body to the other.
When a glass rod is rubbed with silk, the rod becomes positivelycharged while the silk becomes negatively charged. The decrease in the mass of glass rod is equal to the total mass of electrons lost by it.
(ii) Ebonite on rubbing with wool becomes negatively charged making the wool positively charged.
(iii) Clouds also get charged by friction.
(iv) A comb moving through dry hair gets electrically charged. It starts attracting small bits of paper.
(v) During landing or take-off, the tyres of an aircraft get electrified therefore special material is used to manufacture them.
(2) By electrostatic induction : If a charged body is brought near an uncharged body, one side of neutral body (closer
to charged body) becomes oppositely charged while the other side becomes similarly charged.
Induced charge can be lesser or equal to inducing charge (but never greater) and its maximum value is given by where Q is the inducing charge and K is the dielectric constant of the material of the uncharged body. It is also known as specific inductive capacity (SIC) of the medium, or relative permittivity εr of the medium (relative means with respect to free space)
Practice question
When the distance between the charged particles is halved, the force between them becomes
(a) One-fourth(b)Half(c) Double(d) Four times
There are two charges +1 microcoulombs and +5 microcoulombs. The ratio of the forces acting on them will be [CPMT 1979]
(a) 1 : 5(b)1 : 1(c) 5 : 1(d) 1 : 25
A charge exerts some force on a second charge . If third charge is brought near, the force of exerted on [NCERT 1971]
(a) Decreases (b)Increases(c) Remains unchanged
(d) Increases if is of the same sign as and decreases if is of opposite sign
and represents gravitational and electrostatic force respectively between electrons situated at a distance 10 cm. The ratio of is of the order of [NCERT 1978; CPMT 1
(a) (b)10(c) 1 (d)
The ratio of the forces between two small spheres with constant charge in air in a medium of dielectric constant K is [MNR 1998]
(a) 1 :K(b)K : 1(c) (d)
A soap bubble is given a negative charge, then its radius
(a) Decreases (b)Increases(c) Remains unchanged
(d) Nothing can be predicted as information is insufficient
In the absence of other conductors, the surface charge density
(a)Is proportional to the charge on the conductor and its surface area
(b)Inversely proportional to the charge and directly proportional to the surface area
(c)Directly proportional to the charge and inversely proportional to the surface area
(d) Inversely proportional to the charge and the surface area
A body can be negatively charged by CPMT 1972
(a)Giving excess of electrons to it (b)Removing some electrons from it
(c)Giving some protons to it (d)Removing some neutrons from it
The minimum charge on an object is
(a)1 coulomb (b)1 stat coulomb (c)coulomb(d) coulomb
Out of gravitational, electromagnetic, Vander Waals, electrostatic and nuclear forces; which two are able to provide an attractive force between two neutrons
(a)Electrostatic and gravitational (b)Electrostatic and nuclear
(c)Gravitational and nuclear(d)Some other forces like Vander Waals
An isolated solid metallic sphere is given charge. The charge will be distributed on the sphere
(a)Uniformly but only on surface(b)Only on surface but non-uniformly
(c)Uniformly inside the volume(d)Non-uniformly inside the volume
There are two metallic spheres of same radii but one is solid and the other is hollow, then
(a) Solid sphere can be given more charge
(b) Hollow sphere can be given more charge
(c) They can be charged equally (maximum)(d) None of the above
In general, metallic ropes are suspended on the carriers which take inflammable material. The reason is
(a) There speed is controlled
(b) To keep the centre of gravity of the carrier nearer to the earth
(c) To keep the body of the carrier in contact with the earth
(d) Nothing should be placed under the carrier
With the rise in temperature, the dielectric constant of a liquid
(a)Increases(b)Decreases(c)Remains unchanged(d) Charges erratically
When electrons are removed from a neutral metal sphere, the charge on the sphere becomes[Manipal MEE 1995]
(a) (b)(c) (d)
A conductor has positive charge. The conductor has
(a) 9 electrons in excess (b) 27 electrons in short
(c) 27 electrons in excess (d) 9 electrons in short
The value of electric permittivity of free space is[MP PET 1996; RP
(a) (b)
(c) (d)
Number of electrons in one coulomb of charge will be
(a)(b)(c)(d)
A glass rod rubbed with silk is used to charge a gold leaf electroscope and the leaves are observed to diverge. The electroscope thus charged is exposed to X-rays for a short period. Then
(a) The divergence of leaves will not be affected
(b) The leaves will diverge further
(c) The leaves will collapse(d) The leaves will melt
One metallic sphere is given positive charge whereas another identical metallic sphere of exactly same mass as of is given equal amount of negative charge. Then[AMU 1995; RPET 2000;
(a) Mass of and mass of still remain equal
(b)Mass of increases(c)Mass of decreases(d) Mass of increases
When electrons are removed from a neutral metal plate, the electric charge on it is
(a) – 1.6 C(b)+ 1.6 C(c) 10+19C(d)10–19C
Charge on -particle is
(a)(b)(c) (d)
When a glass rod is rubbed with silk, it
(a) Gains electrons from silk (b) Gives electrons to silk
(c) Gains protons from silk (d) Gives protons to silk
A body has – 80 micro coulomb of charge. Number of additional electrons in it will be
(a)(b)(c) (d)
Dielectric constant for metal is
(a) Zero(b)Infinite(c)1 (d)Greater than 1
A charge of Qcoulomb is placed on a solid piece of metal of irregular shape. The charge will distribute itself
(a) Uniformly in the metal object
(b) Uniformly on the surface of the object
(c) Such that the potential energy of the system is minimised
(d) Such that the total heat loss is minimised
Five balls numbered 1 to 5 are suspended using separate threads. Pairs (1, 2), (2, 4) and (4, 1) show electrostatic attraction, while pair (2, 3) and (4, 5) show repulsion. Therefore ball 1 must be
(a)Positively charged(b)Negatively charged (c) Neutral (d)Made of metal
Two identical conductors of copper and aluminium are placed in an identical electric fields. The magnitude of induced charge in thealuminium will be (a)Zero(b)Greater than in copper
(c)Equal to that in copper(d)Less than in copper
When a body is earth connected, electrons from the earth flow into the body. This means the body is…..
(a)Unchanged(b)Charged positively(c)Charged negatively(d)An insulator
Answer 1A 2C 3D 4B 5B 6B 7C 8A 9C 10C 11A 12C 13C 14B 15A 16D 17C 18B 19B 20D 21B 22C 23B 24C 25B 26C 27C 28C 29B
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