1. The thermal radiation from a sphere of radius 10 cm is 150 Watts at a tempera

Question

1. The thermal radiation from a sphere of radius 10 cm is 150 Watts at a temperature of 20 °C. What will be the thermal radiation of the sphere if the temperature is raised to 100°c? A) 375 Watts B) 394 Watts C) 454 Watts D) 212 Watts E) 408 Watts 2. A bubble having a diameter of 1.00 cm is released at the bottom of a resevoir where the depth is 50 m. The water temperature is a constant 16 °C throughout the resevoir. What will be the diameter of the bubble when it reaches the surface? A) 1.69 cm B) 1.89 cm C) 1.80 cm D) 1.43 cm E) 1.57 cm

Explanation / Answer

Question 1) Using the formula ,

P = AT^4

Since A is constant ,

P1/P2 = T1^4/T2^4

Given T1 = 20°C = 293 K

T2 = 100°C = (273 + 100) = 373 K

P1 = 150 W

P1/P2 = T1^4/T2^4

150/P2 = 293^4/373^4

P2 = 150/0.38

P2 = 394 Watts

Answer) option B)394 W

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