If \(2.5 \times 10^{-6\,} N\) average force is exerted by a light wave on a non-reflecting surface of \(30\, cm ^{2}\) area during \(40\) minutes of time span, the energy flux of light just before it falls on the surface is .................. \(W / cm ^{2}\) (Round off to the Nearest Integer) (Assume complete absorption and normal incidence conditions are there)

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.