The area in the Sun's atmosphere located above the chromosphere (1,500-10,000 km) where the temperature rises dramatically is called the:

A) photosphere.
B) corona.
C) solar wind.
D) transition zone.
E) convection zone.


D

Physics & Space Science

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A hydrogen bomb may be approximated by a fireball at a temperature of 7200 K according to a report published in 1950 by the Atomic Energy Commission. (a) Calculate the total rate of radiant-energy emission in watts, assuming that the gas radiates as a blackbody and has a diameter of 1.5 km, (b) If the surrounding atmosphere absorbs radiation below 0.3 determine the per cent of the total radiation emitted by the bomb that is absorbed by the atmosphere, (c) Calculate the rate of irradiation on a 1 m2 area of the wall of a house 40 km from the center of the blast if the blast occurs at an altitude of 16 km and the wall faces in the direction of the blast, (d) Estimate the total amount of radiation absorbed

assuming that the blast lasts approximately 10 sec and that the wall is covered by a coat of red paint, (e) If the wall were made of oak whose flammability limit is estimated to be 650 K and that had a thickness of 1 cm, determine whether or not the wood would catch on fire. Justify your answer by an engineering analysis stating carefully all assumptions.

GIVEN
- A hydrogen bomb fireball
- Fireball temperature (T1) = 7200 K
- Surrounding atmosphere absorbs radiation below 0.3

- The blast occurs at an altitude (H) of 16 km = 16,000 m
FIND
(a) The total rate of radiant-energy emission in watts (qr)
(b) The per cent of the total radiation absorbed by te atmosphere
(c) The rate of irradiation on a 1 m2 area of the wall of a house 40 km (40,000 m) from the center of the blast and facing the blast (G2)
(d) Total amount of radiation absorbed if the blast lasts 10 seconds and the wall is covered with red paint
(e) If the walls are oak with a flammability limit of 650 K and a thickness (s) of 1 cm, will the wood catch fire?
ASSUMPTIONS
- The gas radiates as a blackbody
- Diameter of the fireball (D) = 1.5 km
- The air and surrounding temperature (T?) = 10°C
- The surroundings behave as a blackbody enclosure
- The heat transfer from the oak walls to its surroundings during the 10 seconds of irradiation can be neglected
- The house wall is initially at the surroundings temperature
SKETCH

PROPERTIES AND CONSTANTS
the Stephan-Boltzmann constant

the emissivity of red paint at short wavelengths

the emissivity of red paint at long wavelengths

Specific heat

Thermal conductivity

Density

Thermal diffusivity

Physics & Space Science

Buoyancy: A 200-kg flat-bottomed boat floats in fresh water, which has a density of 1000 kg/m3. If the base of the boat is 1.42 m wide and 4.53 m long, to what depth is the bottom of the boat submerged when it carries three passengers whose total mass is 257 kg?

A. 7.10 cm B. 7.53 cm C. 7.95 cm D. 8.52 cm

Physics & Space Science

An electron is accelerated from rest through a potential difference of 3750 V. It enters a region where the magnetic field is 4.0 mT perpendicular to the velocity of the electron. Calculate the radius of the path this electron will follow

A) 1.2 cm B) 2.2 cm C) 3.2 cm D) 4.2 cm E) 5.2 cm

Physics & Space Science

State the law of reflection

What will be an ideal response?

Physics & Space Science