We know that the electromagnetic wave propagates perpendicular to both electric field and magnetic field which can describe as
$\overrightarrow{k} \times \overrightarrow{E}= \omega \overrightarrow{B} \qquad(1)$
If $\hat{n}$ is a unit vector in the direction of the propagation then
$\overrightarrow{k}=k \hat{n}$
Substitute these values in equation$(1)$ then we get
$k(\hat{n} \times \overrightarrow{E})= \omega \overrightarrow{B}$
$\overrightarrow{B}= \frac{k}{\omega}(\hat{n} \times \overrightarrow{E}) \qquad(2)$
But the value of $k$ and $\omega$ is
$k=\frac{2\pi}{\lambda}$
$\omega=2 \pi \nu$
Then value of $\frac{k}{\omega}=\frac{1}{c}$
Now substitute the value of $\frac{k}{\omega}$ in equation$(2)$ then we get
$\overrightarrow{B}= \frac{1}{c}(\hat{n} \times \overrightarrow{E})$
The magnitude form of the above equation can be written as
$B=\frac{E}{c}$
$\frac{E}{B}=c$
$\frac{E}{\mu_{0}H}=c \qquad (\because B=\mu_{0} H)$
$\frac{E}{H}=\mu_{0}c$
$\frac{E}{H}=\frac{\mu_{0}}{\sqrt{\mu_{0} \epsilon_{0}}} \qquad(\because c=\frac{1}{\sqrt{\mu_{0} \epsilon_{0}}})$
$\frac{E}{H}= \sqrt{\frac{\mu_{0}}{\epsilon_{0}}}$
The term $\frac{E}{H}$ has dimensions of the impedance and is known as characteristic impedance or intrinsic impedance of free space. It is represented by $(Z_{0})$.
$Z_{0}=\frac{E}{H}=\sqrt{\frac{\mu_{0}}{\epsilon_{0}}}$
Now substitute the value of $\mu_{0}$ and $\epsilon_{0}$ i.e.
$\mu_{0}=4\pi \times 10^{-7}$
$\epsilon_{0}=8.854 \times 10^{-12}$
$Z_{0}=\sqrt{\frac{4\pi \times 10^{-7}}{8.854 \times 10^{-12}}}$
$Z_{0}=376.73\: \Omega $
$Z_{0}=120\pi \: \Omega $
Angle of Acceptance → If incident angle of light on the core for which the incident angle on the core-cladding interface equals the critical angle then incident angle of light on the core is called the "Angle of Acceptance. Transmission of light when the incident angle is equal to the acceptance angle If the incident angle is greater than the acceptance angle i.e. $\theta_{i}>\theta_{0}$ then the angle of incidence on the core-cladding interface will be less than the critical angle due to which part of the incident light is transmitted into cladding as shown in the figure below Transmission of light when the incident angle is greater than the acceptance angle If the incident angle is less than the acceptance angle i.e. $\theta_{i}<\theta_{0}$ then the angle of incidence on the core-cladding interface will be greater than the critical angle for which total internal reflection takes place inside the core. As shown in the figure below Transmission of lig
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