Coulomb’s law :
If two point charges q1 and q2 are separated by a distance r in a medium’ then the force of attraction or repulsion F between them is given by,
F = {1\over 4 \pi \epsilon _o \epsilon _r} \times {q_1q_2\over r^2}[\katex]
- Here, ε0 = 8.854 x 10-12C2N-1m-2
- εr = 1 (for air or vacuum)
Electric potential difference :
(a) If W work is done to bring Q coulomb of positive charge from infinity to a particular point in an electric field, then the potential at that point,
V = W/Q or, W = V.Q
(b) If W joule of work is done to move a coulomb of charge from a point A to another point B, then the potential difference between A and B,
VA- VB = W/Q
Electro-Motive Force (EMF) :
If W work is done to move Q charge around a complete circuit, then EMF of the cell,
EMF = W/Q
Electric current :
If a charge 'Q' flows through a cross-section of a conductor in 't' seconds, then the magnitude of current,
Current (I) = Charge (Q) / time (t)
Ohm's Law:
Potential Difference (PD) = Current (I) × Resistance (R)
EMF and internal resistance of a cell:
V = E – I.r
Notation Meaning
- E = EMF
- I = Current
- r = Internal resistance
- V = Terminal voltage
Resistance of a conductor :
Resistance (R) = ρ {l\over A}[\katex]
Notation Meaning
- ρ = resistivity or specific resistance
- l = length of conductor
- A = area of cross-section
