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The electric field of a plane electromagnetic wave is: $ E_y = 69\sin(0.6\times10^3x - 1.8\times10^{11}t)\ \text{V/m} ]$ The expression for the associated magnetic field is:

Options:
  1. $(B_z = 2.3\times10^{-7}\sin(0.6\times10^3x - 1.8\times10^{11}t))$
  2. $(B_z = 2.3\times10^{-7}\sin(0.6\times10^3x + 1.8\times10^{11}t))$
  3. $(B_y = 69\sin(0.6\times10^3x + 1.8\times10^{11}t))$
  4. $(B_y = 2.3\times10^{-7}\sin(0.6\times10^3x - 1.8\times10^{11}t))$

Solution:

For EM wave: $[ B = \frac{E}{c} ]$ $[ B = \frac{69}{3\times10^8} = 2.3\times10^{-7}\ \text{T} ]$ Phase of E and B is same. Direction from right-hand rule → z-direction. ✅ Correct Answer: (1)
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