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The maximum value of E in an electromagnetic wave is equal to 1.8 V m⁻¹. Thus the maximum value of B is ______.

Asked in GSEB Board March 2019 · E0 = cB0 and E/B = c

• (1) 6×10⁻⁸ T
• (2) 3×10⁻⁶ T
• (3) 6×10⁻⁹ T
• (4) 2×10⁻¹⁰ T

Step-by-step solution

Why the other options are wrong

• (1) 6×10⁻⁸ T is 1.8/(3×10⁷): the right division, but with c written as 3×10⁷ instead of 3×10⁸ -- a one-place slip in the power of ten.
• (2) No slip produces 3×10⁻⁶ T. Sanity check: B₀ = (E₀)/c = (1.8)/(3×10⁸) = 6×10⁻⁹ T, which is 500 times smaller than this.
• (4) 2×10⁻¹⁰ T is 1.8/(9×10⁹) -- dividing by the electrostatic constant 9×10⁹ instead of by c, a mix-up of the two big numbers a student carries around.

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