CBSE Class 12 Physics Electric Charges And Field Assignment Set B

Question. A body can be negatively charged by
(a) giving excess of electrons to it
(b) removing some electron from it
(c) giving some protons to it
(d) removing some neutrons from it.

Answer: A

Question. How many electrons must be removed from an electrically neutral metal plate to give it a positive charge of 1 × 10^–7 coulomb?
(a) 6.25 × 10¹¹
(b) 6.45 × 10¹³
(c) 6.25 × 10^–11
(d) 6.45 × 10^–13

Answer: A

Question. The unit of permittivity of free space (e0) is
(a) CN^–1m^–1
(b) Nm²C^–2
(c) C² N–1m^–2
(d) C² N–2m^–2

Answer: C

Question. Which of the following is not a property of field lines?
(a) Field lines are continuous curves without any breaks
(b) Two field lines cannot cross each other
(c) Field lines start at positive charges and end at negative charges
(d) They form closed loops

Answer: D

Question. Gauss's law is valid for
(a) Any closed surface
(b) Only regular closed surfaces
(c) Any open surface
(d) Only irregular open surfaces.

Answer: A

Question. When air is replaced by a medium of dielectric constant K, the force of attraction between two charges separated by a distancer
(a) decreases K times
(b) remains unchanged
(c) increases K times
(d) increases K–2 times

Answer: A

Question. A hemisphere is uniformly charged positively. The electric field at a point on a diameter away from the centre is directed
(a) perpendicular to the diameter
(b) parallel to the diameter
(c) at an angle tilted towards the diameter
(d) at an angle tilted away from the diameter

Answer: A

Question. A point charge +q, is placed at a distance d from an isolated conducting plane. The field at a point P on the other side of the plane is
(a) directed perpendicular to the plane and away from the plane.
(b) directed perpendicular to the plane but towards the plane.
(c) directed radially away from the point charge.
(d) directed radially towards the point charge.

Answer: A

Question. A point charge +q, is placed at a distance d from an isolated conducting plane. The field at a point P on the other side of the plane is 
(a) directed perpendicular to the plane and away from the plane.
(b) directed perpendicular to the plane but towards the plane.
(c) directed radially away from the point charge.
(d) directed radially towards the point charge.

Answer: A

Question. There are two kinds of charges—positive charge and negative charge. The property which differentiates the two kinds of charges is called
(a) amount of charge
(b) polarity of charge
(c) strength of charge
(d) field of charge

Answer: B

Question. A method for charging a conductor without bringing a charged object in contact with it is called
(a) electrification
(b) magnetisation
(c) electromagnetic induction
(d) electrostatic induction

Answer: D

Question. If y E.dS = 0 over a surface, then
(a) the electric field inside the surface and on it is zero.
(b) the electric field inside the surface is necessarily uniform.
(c) the number of flux lines entering the surface must be equal to the number of flux lines leaving it.
(d) all charges must necessarily be outside the surface.

Answer: C, D

Question. A cup contains 250 g of water. The number of negative charges present in the cup of water is
(a) 1.34 × 107 C
(b) 1.34 × 1019 C
(c) 3.34 × 107 C
(d) 1.34 × 10–19 C

Answer: A

Question. When the distance between two charged particles is halved, the Coulomb force between them becomes
(a) one-half
(b) one-fourth
(c) double
(d) four times.

Answer: D

Question. Two charges are at distance d apart in air. Coulomb force between them is F. If a dielectric material of dielectric constant K is placed between them, the Coulomb force now becomes
(a) F/K
(b) FK
(c) F/K²
(d) K²F

Answer: A

Question. Two point charges q₁ and q₂ are at separation r. The force acting between them is given by F = K (q₁ q₂ / r²) . The constant K depends upon
(a) only on the system of units
(b) only on medium between charges
(c) both on (a) and (b)
(d) neither on (a) nor on (b)

Answer: C

Question. Three charges +4q, Q and q are placed in a straight line of length l at points at distance 0, l/2, and l respectively. What should be Q in order to make the net force on q to be zero?
(a) –q
(b) –2q
(c) – (q/2)
(d) 4q

Answer: A

Question. An electron falls from the rest through a vertical distance h in a uniform and vertically upward directed electric field E. The direction of electric field is now reversed, keeping its magnitude the same. A proton is allowed to fall from rest in it through the same vertical distance h. The time of fall of the electron, in comparison to the time of fall of the proton is
(a) smaller
(b) 5 times bigger
(c) 10 times bigger
(d) equal

Answer: A

Question. Two point charges A and B, having charges +q and –q respectively, are placed at certain distance apart and force acting between them is F. If 25% charge of A is transferred to B, then force between the charges becomes:
(a) F
(b) 9F/16
(c) 16F/3
(d) 4F/3

Answer: B

Fill in the Blanks

Question. The quantisation of charge was experimentally demonstrated by _______________ in 1912.
Answer: Millikan

Question. The value of the permittivity of free space (e0) in SI unit is _______________.
Answer: 8.854 × 10^–12 C²N^–1m^–2

Question. A simple apparatus to detect charge on a body is the _______________.
Answer: gold-leaf electroscope

Question. The process of sharing the charges with the earth is called _______________.
Answer: grounding or earthing

Question. The concept of field was first introduced by _______________ and is now among the central concepts in physics.
Answer: Faraday

Question. Two point charges are separated by some distance inside vacuum. When space between the charges is filled by some dielectric, the force between two point charges _______________.
Answer: decreases

Question. Two point charges, one coulomb each are separated by vacuum and placed I meter apart from each other. The force acting between them is _______________.
Answer: 9 × 10⁹ N

Question. Direction of electric field intensity due to a dipole on equatorial point is _______________ to the direction of dipole moment.
Answer: opposite

Question. Two equal and opposite charges of magnitude 0.2 × 10^–6 C are 15 cm apart, the magnitude and direction of the resultant electric intensity E at a point midway between the charge is ___________.
Answer: 6.4 × 10⁵ N/C, towards the –ve charge

Question. A proton at rest has a charge e. When it moves with high speed v, its charge is _______________.
Answer: e