Electrostatics — Class 12 Physics Notes
1. Introduction to Electrostatics
Electrostatics deals with the study of electric charges at rest.
The fundamental charge is the charge of an electron:
e=1.6×10−19 Ce = 1.6 \times 10^{-19} \, \text{C}e=1.6×10−19C
Charges can be positive (+) or negative (−).
Like charges repel, unlike charges attract.
2. Coulomb’s Law
The force FFF between two point charges q1q_1q1 and q2q_2q2 separated by a distance
rrr in vacuum is:
F=k∣q1q2∣r2F = k \frac{|q_1 q_2|}{r^2}F=kr2∣q1q2∣
where k=14πϵ0=9×109 Nm2/C2k = \frac{1}{4\pi \epsilon_0} = 9 \times 10^9 \,
\text{Nm}^2/\text{C}^2k=4πϵ01=9×109Nm2/C2.
The force acts along the line joining the charges.
3. Electric Field E⃗\vec{E}E
The electric field at a point is the force per unit positive charge placed at that point:
E⃗=F⃗q\vec{E} = \frac{\vec{F}}{q}E=qF
Electric field due to a point charge QQQ at distance rrr:
1. Introduction to Electrostatics
Electrostatics deals with the study of electric charges at rest.
The fundamental charge is the charge of an electron:
e=1.6×10−19 Ce = 1.6 \times 10^{-19} \, \text{C}e=1.6×10−19C
Charges can be positive (+) or negative (−).
Like charges repel, unlike charges attract.
2. Coulomb’s Law
The force FFF between two point charges q1q_1q1 and q2q_2q2 separated by a distance
rrr in vacuum is:
F=k∣q1q2∣r2F = k \frac{|q_1 q_2|}{r^2}F=kr2∣q1q2∣
where k=14πϵ0=9×109 Nm2/C2k = \frac{1}{4\pi \epsilon_0} = 9 \times 10^9 \,
\text{Nm}^2/\text{C}^2k=4πϵ01=9×109Nm2/C2.
The force acts along the line joining the charges.
3. Electric Field E⃗\vec{E}E
The electric field at a point is the force per unit positive charge placed at that point:
E⃗=F⃗q\vec{E} = \frac{\vec{F}}{q}E=qF
Electric field due to a point charge QQQ at distance rrr:
