Question

estimate the radiant power loss from a human body at a temperature 38°C to the environment at 0°C if the surface area if the body is 1.5 m square and emissivity is 0.6 (stefan constant = 5.67× 10^-8 Wm^-2 K ^ -4)​

Answer 1

Answer:

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Find the area of a triangle, two sides of which are 18cm and 10cm and the perimeter is 42 cm :

Answer :-

Given that,

Two sides of triangle are 18 cm and 10 cm.

Perimeter of triangle is 42 cm

Let, third side of triangle be x .

So,

⟶ Perimeter = 18 + 10 + x

⟶ 42 = 28 + x

⟶ 42 - 28 = x

⟶ x = 14

Third side of triangle is 14 cm.

Now,

s = 42/2

s = 21

Semi-perimeter is 21 cm.

Area of traingle :

⟶ √21 × (21 -18)(21 -14)(21 - 10)

⟶ √21 × 3 × 7 × 11

⟶ √3 × 7 × 3 × 7 × 11

⟶ 3 × 7 √11

⟶ 21 × √11

Put √11 = 3.316

⟶ 21 ×3.316

$\longrightarrow \blue{\boxed{\bold{69.639}}\bigstar}$

★

Area of triangle is 69.636 cm²

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Formulas used:-

• Perimeter of triangle = Sum of all sides

• Heron's formula that is

Area of traingle = √s(s - a)(s - b)(s - c)

where,

s is semi-perimeter of triangle.

a, b and c are sides of triangle.

• Semi-perimeter = Perimeter of triangle/2

Answer 2

Answer:
The answer is 193.93 Watt.

Explanation:

Given Values :

• Temperature of the Human Body ( T₁ ) = 38 °C = 311 K
• Temperature of the Environment ( T₀ ) = 0 °C = 273 K
• Surface Area of the body ( A ) = 1.5 m²
• Emissivity ( e ) = 0.6
• Stefan's Constant ( σ ) = 5.67×10⁻⁸ Wm⁻²K⁻⁴

Now,

From Stefan's Law,

Radiant Power Loss ( P ) = σ A e ( T₁⁴ - T₀⁴ )

Replacing given values in the above equation

    P = 5.67×10⁻⁸×1.5×0.6(311⁴-273⁴)

∴   P = 193.93 Watt