The calorie was originally defined as the amount of heat required at a pressure of 1 standard atmosphere to raise the temperature of 1 gram of water 1° Celsius. ... Since 1925 this calorie has been defined in terms of the joule, the definition since 1948 being that one calorie is equal to approximately 4.2 joules.
Answer:
31.8 × 10⁻⁴ J = 3.18 mJ
Explanation:
We know the intensity I of a wave is I = P/A where P = power and A = area = 0.500 m²
The intensity of an electromagnetic wave is also equal to I = E₀²/μ₀c
where E₀ = maximum electric field strength = √2E where E = rms value of electric field = 0.0200 N/C, μ₀ = 4π × 10⁻⁷ H/m ,c = 3 × 10⁸ m/s
P/A = E₀²/μ₀c = 2E²/μ₀c
P = 2E²A/μ₀c = 2 × (0.02 N/C)² × 0.5 m²/(4π × 10⁻⁷ H/m × 3 × 10⁸ m/s)
= 1.06 × 10⁻⁴ W = 0.106 mW
Since P = E/t where E = Energy and t = time
E = Pt with t = 30 s
E = 1.06 × 10⁻⁴ W × 30 s = 31.8 × 10⁻⁴ J = 3.18 mJ
So the wave carries 3.18 mJ of energy through the window in 30 s
