The numerical value (magnitude) of electric force between two charges depend on the,
(i) value of charges on them,
(ii) distance between them and
(iii) nature of medium between them.

a. Comb gained electrons. Dry hair lost electron.
b. No. of electrons transferred = - 0.4 C
1 coulomb 6.25 x 10¹⁸ electron
- 0.4 C = 0.4 x 6.25 x 10¹⁸ electron
= - 2.5 x 10¹⁸ electrons

Effective resistance of the
series combination of R₁ & R₂
Effective resistance of the parallel combination of
R¹ = R₁ + R₂ = R + R = R\(\Omega \)
Effective resistance of the entire circuit,
R₃ & R₄
\(\cfrac { 1 }{ { R }^{ 11 } } =\cfrac { 1 }{ { R }_{ 3 } } +\cfrac { 1 }{ { R }_{ 4 } } \)
\(\cfrac { 1 }{ { R }^{ 11 } } =\cfrac { 1 }{ R } +\cfrac { 1 }{ R } =\cfrac { 2 }{ R } \)

Effective resistance of the entire circuit,
\(\cfrac { 1 }{ { R }_{ P } } =\cfrac { 1 }{ { R }^{ 1 } } +\cfrac { 1 }{ { { R }^{ 11 } } } \)
\(=\cfrac { 1 }{ 2R } +\cfrac { 2 }{ R } =\cfrac { 1+4 }{ 2R } =\cfrac { 5 }{ 2R } \)
\({ R }_{ P }=\cfrac { 2 }{ 5 } R\Omega \)

Slope of V - 1 graph is resistance of the conductor.
Since slope of A is greater than the slope of B.
\(\therefore \) R_A > R_B
Series: R_s = 12 + 6 = 180\(\Omega \) \(\Rightarrow \)R_A
Parallel:
\(\cfrac { 1 }{ { R }_{ P } } =\cfrac { 1 }{ 12 } +\cfrac { 1 }{ 6 } =\cfrac { 1+2 }{ 12 } =\cfrac { 3 }{ 12 } \) 
\({ R }_{ P }=\cfrac { 12 }{ 3 } =4\Omega \Rightarrow { R }_{ B }\)
Hence, graph A represents series combination and graph B represents parallel combination

The electric current is defined as the rate of flow of electric charge through any section of a conductor.
Electric current I = \(\cfrac { Q }{ t } \)
Its unit is Cs^-1
Its SI unit: ampere (A).

Electric field is the region around a charged body within which its influence can be experienced (i.e) within which it can attract or repel another charged body.

The lines representing the electric field are called electric lines of force

No it is not possible with alternating current. It is possible with direct current.

No, its terminals are not constant because it is the source of direct current. The dc is due to the unidirectional flow of electric charges. In electrical circuits electrons move from lower to higher electrical potential. So battery is used to maintain a potential difference between the two ends.

Birds can sit on power lines and not get electric shocks because the electricity is always looking for a way to get to the ground (i.e.) the current is not flowing out of its body to any other material.
Current flows in a loop (which means the circuit is closed). A bird sitting on a transmission line does not complete the circuit. If the same bird keeps one leg on one line and another leg or any part of its body on another line or the neutral points, then it will get burnt.