Current and Electricity Formulas for jee and neet

 

Current and Electricity Formulas

1. Current

I = neAVd

The number of free electrons per unit volume is denoted by n.

A is the cross-sectional area.

The electron’s charge is denoted by the letter e.

Vd is the drift velocity.

2. Current Density

j = i/A = σE

i is the current

The letter A represents the cross-sectional area.

The electric density is denoted by E.

σ is the conductivity.

3. Wire resistance

R =ρl/A, where ρ=1/σ

ρ is the resistivity

σ is the conductivity.

4. Temperature dependence of resistance

R=R0(1+ αΔT)

R0 is the original resistance

R is the resistance at temperature T

α is the temperature coefficient of resistance.

5. Ohm’s law

V=IR

The voltage is represented by the letter V.

I is the current

R stands for resistance.

6. Kirchhoff’s Law

(i) Junction Law: The algebraic total of all currents flowing into a node is zero.

i.e., ∑node Ii=0.

(ii) The Loop Law: In a circuit, the algebraic total of all potential differences in a closed loop is zero.

i.e., ∑loop ΔVi=0.

7. Parallel resistance

1/Req = 1/R1 +1/R2

8. In-series resistance

Req = R1 +R2

9. Electric Power

P = V2/R=I2R =IV

10. Charging of capacitors

q(t) = CV(1- e-t/RC)

11. Discharging of capacitors

q(t) = q0e-t/RC

12. Time Constant in RC circuit

τ = RC

13. Faraday’s law of electrolysis

The amount of mass deposited is

m= Zit = (1/F)Eit

Where I denotes the current and t denotes the time.

Z stands for the electrochemical equivalent.

The chemical equivalent is E.

The Faraday constant is F = 96485 C/g.

14. Wheatstone bridge

In a Wheatstone bridge that is well-balanced,

R/S = P/Q