RBSE Class 12 Physics Chapter 1 — Electric Charges and Fields: Most Repeated Questions (2013–2026)

∮E⋅dA=Q_enc/ε₀

Surface Charge density σ

Total Flux over the entire surface of cylinder

ϕ=∮_S1E⃗⋅dS⃗+∮_S2E⃗⋅dS⃗+∮_S3E⃗⋅dS⃗; ϕ=∫_S1Edscos0^∘+∫_S2Edscos0^∘+∫_S3Edscos90^∘; ϕ=E∮_S1ds+E∮_S2ds+0; ϕ=ES+ES=2ES

According to Gauss's Law

ϕ=∑q/ϵ₀; 2ES=σS/ϵ₀; E=σ/2ϵ₀

All 32 solved questions for this chapter are in the full RBSE Physics PYQ book.

Gauss’s law says that the total electric flux passing through any closed surface is equal to 1/ε₀ times the net charge enclosed inside that surface

∮E⋅dA=Q_enc/ε₀

All 32 solved questions for this chapter are in the full RBSE Physics PYQ book.

The electric flux through a given surface is a measure of the total number of electric field lines passing normally through that surface

Field due to an infinitely long straight uniformly charged wire:

Consider an infinitely long thin wire with uniform linear charge density λ

The electric field at every point in the plane cutting the wire normally is radial and its magnitude depends only on the radial distance r

Now consider a circular closed cylinder of radius r and length L with the infinitely long line of charge as its axis

So the total electric flux over the surface

ϕ=∮E⃗⋅ds⃗=∫_S1Edscos0^∘+∫_S2Edscos90^∘+∫_S3Edscos90^∘; ϕ=E∮_S1ds=E×2πrL

Charge inside the cylinder (q_L)=λL # Now according to Gauss's theorem ϕ=q/ϵ₀ So

E×2πrL=λL/ϵ₀; E⃗=λ/2πϵ₀rr̂; E⃗=λ/2πϵ₀rr̂; E⃗=1/4πϵ₀2λ/rr̂ ;

E∝1/r

All 32 solved questions for this chapter are in the full RBSE Physics PYQ book.

E₁=1/4πϵ₀q/((r²+a²)²)

Electric field intensity due to -q

E₂=1/4πϵ₀q/((r²+a²)²)

THE TOTAL ELECTRIC FIELD

E_eq =E_+qcosθ+E_-qcosθ or E=E₁cosθ+E₂cosθ

=2E_+qcosθ

=E=1/4πϵ₀2qa/((r²+a²)^3/2)

for (r≫a)

E=1/4πϵ₀2qa/r³

E⃗_q=KP/r³

All 32 solved questions for this chapter are in the full RBSE Physics PYQ book.

Electric dipole moment is defined as the product of the magnitude of either charge and the distance between the two charges of the dipole

p=q×d

It is always directed from negative charge to positive charge

All 32 solved questions for this chapter are in the full RBSE Physics PYQ book.