Question

The magnetic field in a plane electromagnetic wave travelling in glass \((n = 1.5)\) is given by \[ B_y=(2\times10^{-7}\,\text{T})\sin(\alpha x+1.5\times10^{11}t) \] where \(x\) is in metres and \(t\) is in seconds. The value of \(\alpha\) is:

• A. \(0.5\times10^3\ \text{m}^{-1}\)
• B. \(6.0\times10^2\ \text{m}^{-1}\)
• C. \(7.5\times10^2\ \text{m}^{-1}\)
• D. \(1.5\times10^3\ \text{m}^{-1}\)

Hint:

For an electromagnetic wave, \[ v=\frac{\omega}{k} \] and \[ v=\frac{c}{n}. \] Therefore, \[ k=\frac{\omega n}{c}. \] This direct formula is often the fastest way to solve such questions.

Answer 1

The Correct Option is C