PiTheory

Electromagnetic Waves formulas

Class 12 physics formula sheet for NEET and JEE: the key equations of NCERT chapter 8, the special cases questions are built on, and diagrams where they help.

16 formulas4 sectionsClass 12 · Chapter 81 of 4 sections free

By Sreeraj P, M.Sc Physics · 10+ years teaching NEET and JEE

Most used formulasOther formulas and cases

1Displacement current

$$i_d=\varepsilon_0\frac{d\phi_E}{dt}=C\frac{dV}{dt}$$

Changing electric flux acts like a current (between capacitor plates while charging). Inside the gap $i_d=i_c$; the total $i_c+i_d$ is continuous.

$$\oint\vec B\cdot d\vec l=\mu_0\left(i_c+\varepsilon_0\frac{d\phi_E}{dt}\right)$$

Ampère–Maxwell law. Between circular plates (radius $R$): $B=\dfrac{\mu_0i_dr}{2\pi R^2}$ for $r<R$, $\dfrac{\mu_0i_d}{2\pi r}$ outside. Displacement current through a smaller area $\pi r^2$: $i_d\dfrac{r^2}{R^2}$.

$$\oint\vec E\cdot d\vec A=\frac{q}{\varepsilon_0},\ \ \oint\vec B\cdot d\vec A=0,\ \ \oint\vec E\cdot d\vec l=-\frac{d\phi_B}{dt}$$
$$\begin{array}{l}\displaystyle \oint\vec E\cdot d\vec A=\frac{q}{\varepsilon_0}\\[6pt]\displaystyle \ \oint\vec B\cdot d\vec A=0\\[6pt]\displaystyle \ \oint\vec E\cdot d\vec l=-\frac{d\phi_B}{dt}\end{array}$$

With the Ampère–Maxwell law: Maxwell's four equations. Force on a charge: $\vec F=q(\vec E+\vec v\times\vec B)$.

3 more sections and 13 formulas in the full chapter

  1. 2Electromagnetic waves7 formulas · 1 diagram
  2. 3Energy, intensity, momentum6 formulas
  3. 4Electromagnetic spectrum1 case table

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