If 2.5*10-9 N average force is exerted by a light wave on a non- reflecting surface of 30 cm2 area during 40 minutes of time span, the energy flux of light just before it falls on the surface is ................ W / cm2. (Round off to the Nearest Integer) (Assume complete absorption and normal incidence conditions are there)
If 2.5*10-9 N average force is exerted by a light wave on a non- reflecting surface of 30 cm2 area during 40 minutes of time span, the energy flux of light just before it falls on the surface is ................ W / cm2. (Round off to the Nearest Integer) (Assume complete absorption and normal incidence conditions are there)
The force (F) exerted by radiation is the rate of change of momentum (p).
F = Δp/Δt
For photons, p = E/c. So, F = (1/c) * (ΔE/Δt).
Since Power (P) is ΔE/Δt, F = P/c.
Intensity (I) is Power per unit Area (P/A).
The formula provided in the document is F/A = (nE)/ (Δt c A) which leads to a final calculated
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According to definition of displacement current, we can write
B0 = 42.9 × 10-9
42.9 Ans
s? = -? + k? ∴ s? = (-? +k? )/√2
I = P/ (4πr²) . (i)
and I = (1/2)ε? E? ²c . (ii)
From (i) and (ii)
P/ (4πr²) = (1/2)ε? E? ²c
E? = √ (2P/ (4πε? r²c) ; E? = √ (9×10? ×2×15)/ (15×15×10? ×3×10? ) = 2×10? ³ V/m
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