Electric charge & Electric field
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Q- Which experiment is related to the discovery of charge?
A- Millicon`s oil drop method
Q-Why electric field is zero inside the conducting sphere, cavity ?
A-Because charge remains at the outer surface of conducting body. so no charge inside the conductor. it means electric field is also zero.
Q-Define electric field? what is electric field intensity? give unit also.
A-Surrounding area of a charge , where another test charge experience an electrostatic force , known as electric field.
the magnitude of electrostatic force experienced by a unit test charge at a point in electric field is known as intensity of electric field at that point.
intensity of electric field E=F/q0
Q- Explain main properties of electric field lines. .
A-“(i) Field lines start from positive charges and end at negative charges. If there is a single charge, they may start or end at infinity.
(ii) In a charge-free region, electric field lines can be taken to be continuous curves without any breaks.
(iii) Two field lines can never cross each other. (If they did, the field at the point of intersection will not have a unique direction, which is absurd.)
(iv) Electrostatic field lines do not form any closed loops. This follows from the conservative nature of electric field.”
Note-They cannot intersect with each other at any point. The electric field intensity at a single point can never have two directions. So we cannot draw two tangents originating from the same point.
But field lines can be perpendicular to the direction of charge when the electric is field is non-uniform. In a uniform one, the lines are parallel to each other.
Q-Why do the electric field lines not form closed loops?
A-Electric field lines never form closed loops as we should know the electrostatic field is conservative. In a conservative field, the work done in moving a charge around any closed path is zero. If lines formed loops, a charge would keep gaining energy along the path, which breaks this rule of zero net work.
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Q-When a body is positively charged , its mass increases or decreases?
A-mass decreases.
Q- For 1 coulomb charge , number of transferable electron?
A- 6.25X10^28 electrons.
Q-Explain the meaning of the statement ‘electric charge of a body is quantised’.
A-The ‘electric charge of a body is quantized’ means that only integral (1, 2, …n) numbers of electrons can be transferred from one body to another.
Charges cannot get transferred in fractions. Hence, the total charge possessed by a body is only in integral multiples of electric charge.
Q-An electrostatic field line is a continuous curve. That is, a field line cannot have sudden breaks. Why not?
Q-What is the force between two small charged spheres having charges of 2 ×10-7C and 3 × 10–7C placed 30 cm apart in air?
A-When a charge is placed in an electrostatic field, then it experiences a continuous force. Therefore, an electrostatic field line is a continuous curve. And a charge moves continuously and does not jump from one point to the other. So, the field line cannot have a sudden break.
A-Repulsive force of magnitude 6 × 10−3 N
Charge on the first sphere, q1 = 2 × 10−7 C
Charge on the second sphere, q2 = 3 × 10−7 C
Distance between the spheres, r = 30 cm = 0.3 m
Electrostatic force between the spheres is given by the relation:
F = (1/4πε0). (q1q2)/ (r2)
Where, ε0 = Permittivity of free space and (1/4πε0) =9 × 109 Nm2C−2
Therefore, force F = (9 × 109 × 2 × 10−7)/ ((0.3)2)
= 6 × 10−3N
Hence, force between the two small charged spheres is 6 × 10−3 N. The charges are of same nature. Hence, force between them will be repulsive.
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Q-Figure shows tracks of three charged particles in a uniform electrostatic field. Give the signs of the three charges.
A- (1) negative , (2) negative ( less magnitude) ( 3) positive charged