If and denote electric and magnetic fields respectively, which of the following is dimensionless?

Question

If  and  denote electric and magnetic fields respectively, which of the following is dimensionless?

Canvas Classes · Accepted Answer

🧠 In an EM Wave,  Equals  — and  Equals

For an electromagnetic wave the field magnitudes obey , so . Combine that with  and the product becomes a pure number.

🗺️ Working It Out

So

which is dimensionless.

⚡ The Smart Move

Spot the two velocity-like quantities:  has units of speed (), and  is also . Their ratio is dimensionless.

⚠️ Where Students Get Stuck

Trying to check dimensions term by term. The clean route is " and ," whose product is exactly 1.

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