Why might we suspect that a black hole in a binary system could emit X-rays?
What will be an ideal response?
If matter flows into a black hole, it will whirl through an accretion disk and become hot enough to emit X-rays before it reaches the event horizon.
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Answer the following statement true (T) or false (F)
Two infinitely large black plane surfaces are 0.3 m apart and the space between them is filled by an isothermal gas mixture at 811 K and atmospheric pressure consisting of 25% CO2, 25% H2O, and 50% N2 by volume. If one of the surfaces is maintained at 278 K and the other at 1390 K respectively, calculate
(a) the effective emissivity of the gas at its temperature
(b) the effective absorptivity of the gas to radiation from the 1390 K surface
(c) the effective absorptivity of the gas to radiation from the 278 K surface
(d) the net rate of heat transfer to the gas per square meter of surface area
GIVEN
Two infinitely large black plane surfaces with an isothermal gas mixture between them
Distance between surfaces (s) = 0.3 m
Gas mixture temperature (Tm) = 811 K
Gas mixture pressure = 1 atm
Gas contents: 25% CO2, 25% H2O, 50 % N2 by volume
Surface temperatures
T1 = 278 K
T2 = 1390 K
FIND
(a) The effective emissivity of the gas at its temperature (? mix)
(b) The effective absorptivity of the gas to radiation from A1
(c) The effective absorptivity of the gas to radiation from A2
(d) The net rate of heat transfer to the gas per square meter of surface are (qm/A)
ASSUMPTIONS
Steady state
Convection is negligible
SKETCH
Two cooks standing side by side in a restaurant pull their beaters out of the dough at the same instant. A glob of dough flies off each beater. Each glob lands on the top of a tin the same horizontal distance away and at its initial height. However, one lands later than the other. The explanation is that they left the beaters at angles ?1 and ?2 such that:
A.
B.
.C.
.D.
E.
Buoyancy: A 50-cm3 block of wood is floating on water, and a 50-cm3 chunk of iron is totally submerged in the water. Which one has the greater buoyant force on it?
A. the wood B. the iron C. Both have the same buoyant force. D. It cannot be determined without knowing their densities.