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Electromagnetic Waves formula sheet

Every formula in the Electromagnetic Waves chapter for JEE Main, with one line on when it applies. Topic 1 is open to everyone; sign in free to read all 18 and download the PDF.

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How we count: 7× asked means 7 past JEE Main questions in the PrepWiser bank needed that formula, and "last" is the latest year one appeared. ★ marks formulas asked 8 or more times.

Displacement current and Maxwell's equations

Displacement current
8× asked, last 2026
Id=ε0dΦEdt=ε0AdEdt=CdVdtI_d=\varepsilon_0\frac{d\Phi_E}{dt}=\varepsilon_0A\frac{dE}{dt}=C\frac{dV}{dt}
Equals the wire current. AC: peak CV0ωCV_0\omega. Dielectric: ε0→Kε0\varepsilon_0\to K\varepsilon_0.
Field between the plates
B=μ0Idr2πR2 (r<R),B=μ0Id2πr (r≥R)B=\frac{\mu_0I_dr}{2\pi R^2}\ (r<R),\qquad B=\frac{\mu_0I_d}{2\pi r}\ (r\ge R)
Circular plates of radius RR.
Conduction vs displacement
2× asked, last 2026
Jc=σE,Jd=ε∂E∂t,Jc,max⁡Jd,max⁡=σωεJ_c=\sigma E,\qquad J_d=\varepsilon\frac{\partial E}{\partial t},\qquad \frac{J_{c,\max}}{J_{d,\max}}=\frac\sigma{\omega\varepsilon}
E=E0sin⁡ωtE=E_0\sin\omega t; ε=Kε0\varepsilon=K\varepsilon_0.
Maxwell's equations
5× asked, last 2026
∮E⃗⋅dA⃗=qencε0,∮B⃗⋅dA⃗=0∮E⃗⋅dl⃗=−dΦBdt,∮B⃗⋅dl⃗=μ0(Ic+ε0dΦEdt)\begin{aligned}&\oint\vec E\cdot d\vec A=\frac{q_{\text{enc}}}{\varepsilon_0},\qquad \oint\vec B\cdot d\vec A=0\\&\oint\vec E\cdot d\vec l=-\frac{d\Phi_B}{dt},\qquad \oint\vec B\cdot d\vec l=\mu_0\left(I_c+\varepsilon_0\frac{d\Phi_E}{dt}\right)\end{aligned}
Gauss (E), Gauss (B), Faraday, Ampère–Maxwell.

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Practise Electromagnetic Waves

14 more formulas in 5 topics

Nature and speed of EM waves; Wave equation and directions; Energy and intensity; Momentum, pressure and force on charges; and Electromagnetic spectrum. Read the first part free. Sign in free with Google to read the rest and download the PDF.

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Nature and speed of EM waves

  • Speed in vacuum and a medium15×
  • E–B relation31×

Wave equation and directions

  • Directions of E, B and travel31×
  • Plane-wave equation15×

Energy and intensity

  • Energy density7×
  • Average energy density7×
  • Intensity11×
  • Point source6×

Momentum, pressure and force on charges

  • Momentum of an EM wave4×
  • Radiation pressure6×
  • Force on a charge in the wave6×

Electromagnetic spectrum

  • Order of the spectrum7×
  • Wavelength ranges2×
  • Sources and uses3×

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About 135 past JEE Main questions from this chapter, with instant answer checking and step-by-step solutions where available. Free, and you can start without signing up.

Practise Electromagnetic Waves

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