Study Notes
An electric field is a region where an electric charge experiences a force. It is characterized by field lines that indicate the direction of the force on a positive test charge.
- Electric Field Strength (E) — The electrostatic force per unit positive charge. Example: Calculated using E = F/Q, where F is the force and Q is the charge.
- Coulomb's Law — The force between two charges is proportional to the product of their charges and inversely proportional to the square of their separation distance. Example: FE = k * |Q1 * Q2| / r², where k is Coulomb's constant.
- Potential Gradient — The rate of change of electric potential with distance. Example: E = -ΔV/Δr, where ΔV is the change in potential and Δr is the change in distance.
- Electric Potential — The work done per unit charge to move a charge from infinity to a point in space. Example: V = Q / (4πε0r), where Q is the charge and r is the distance from the charge center.
Exam Tips
Key Definitions to Remember
- Electric Field Strength: Force per unit positive charge.
- Coulomb's Law: Force between two charges is proportional to the product of their charges and inversely proportional to the square of their separation.
- Electric Potential: Work done per unit charge to move a charge from infinity to a point.
Common Confusions
- Direction of electric field lines: They point away from positive charges and toward negative charges.
- Difference between electric field and electric potential: Field is a vector, potential is a scalar.
Typical Exam Questions
- What is the direction of the electric field around a positive charge? Away from the charge.
- How does the electric field strength change with distance from a point charge? It decreases with the square of the distance.
- What happens to the force between two charges if the distance between them is halved? The force increases by a factor of four.
What Examiners Usually Test
- Understanding of electric field direction and strength.
- Application of Coulomb's Law to calculate forces between charges.
- Calculation of electric potential and potential energy changes.