IIT JEE Physics Practice Paper – Electrostatics (Set 12)
Instructions
Total Questions: 20 | Marks: 4 each | No Negative Marking
Electrostatics – IIT JEE Notes (Set 12)
Electric Charge
Basic Concept
Electric charge is a fundamental property of matter responsible for electric forces. There are two types of charges: positive and negative. Like charges repel each other, while unlike charges attract.
Quantization of Charge
Charge exists in discrete units: q = ne, where e = 1.6 × 10⁻¹⁹ C.
Coulomb’s Law
Formula
F = k (q₁q₂) / r²
Explanation
The electrostatic force between two point charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.
Electric Field
Definition
Electric field is the force experienced by a unit positive charge placed in a region.
Formula
E = F / q
Due to Point Charge
E = kq / r²
Electric Field Lines
Properties
Electric field lines originate from positive charges and terminate on negative charges. They never intersect and indicate direction of the electric field.
Key Insight
Closer field lines indicate stronger electric field.
Electric Potential
Definition
Electric potential is the work done per unit charge in bringing a charge from infinity to a point.
Formula
V = kq / r
Potential Difference
Concept
Potential difference is the work done per unit charge in moving a charge between two points.
Relation
V = W / q
Equipotential Surfaces
Definition
Surfaces having the same electric potential at every point.
Key Insight
No work is done in moving a charge along an equipotential surface.
Electric Field in Conductors
Important Concept
In electrostatic equilibrium, the electric field inside a conductor is zero.
Charge Distribution
Charge resides on the surface of the conductor.
Gauss’s Law
Statement
The total electric flux through a closed surface is equal to the charge enclosed divided by permittivity.
Formula
Φ = Q / ε₀
Electric Flux
Definition
Electric flux is the measure of electric field passing through a surface.
Formula
Φ = EA cosθ
Unit
Nm²/C
Capacitance
Definition
Capacitance is the ability of a system to store charge.
Formula
C = Q / V
Unit
Farad (F)
Parallel Plate Capacitor
Formula
C = ε₀A / d
Key Insight
Capacitance increases with area and decreases with separation between plates.
Energy Stored in Capacitor
Formula
U = (1/2)CV²
Alternative Forms
U = (1/2)QV = Q² / (2C)
Dielectrics
Concept
Dielectric materials increase capacitance by reducing effective electric field between plates.
Effect
C increases by factor K (dielectric constant).
Electric Field Due to Charge Distributions
Infinite Line Charge
E ∝ 1/r
Infinite Plane Sheet
Electric field is constant and does not depend on distance.
Force and Motion of Charges
Force
F = qE
Key Insight
Positive charges move along field lines, while negative charges move opposite.
Important Relationships
Relation Between E and V
E = -dV/dx
Field Direction
Electric field always points from higher potential to lower potential.
Conceptual Insights
Key Understanding
Electric field and potential are closely related but not the same. Field represents force, while potential represents energy per unit charge.
Common Mistakes
Students often confuse electric field with electric potential and assume both behave similarly.
Important Exam Concepts
Conceptual Traps
Electric field inside conductor is zero. Equipotential surfaces are perpendicular to electric field lines.
JEE Strategy
Focus on formulas, diagrams, and problem-solving involving Gauss’s law and capacitors. Practice numerical problems on electric field and potential thoroughly.