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Question
Assume early universe was composed only of Helium instead of Hydrogen. a) Estimate the temperature of CMB when Helium recombination occurred. Suppose that all the CMB photons have the average energy of the black body spectrum. b) Repeat your approximation of the temperature, but now assume that you only need 1 photon per Helium atom to keep the atoms ionized. Also suppose fraction of photons with energy greater than E in a black body spectrum is approximately, exp (-E/kT) c) guess scale factor of the Universe when Helium recombination occurred using your two different answers in part a and b.
When a mass of 25 g is attached to a certain spring, it makes 19 complete vibrations in 4.5 s. What is the spring constant of the spring
The amount of heat added is 6.3 kJ, of which one-third is added at constant volume and the remainder at constant pressure. Calculate (a) the energy transfer for each of the components
Find the radius of the largest water drop
The potter can stop the wheel in 7.0 s by pressing a wet rag against the rim and exerting a radially inward force of 68 N. Find out the effective coefficient of kinetic friction between the wheel and the wet rag.
Two identical light bulbs of 60w and 120v are connected in parallel and these arre then connected across a 120v power source
An undersea research chamber is spherical with an external diameter of 4.60m . The mass of the chamber, when occupied, is 51100kg. What is the buoyant force on the chamber
Two electrodes are placed in a calcium chloride solution and a potential difference is maintained between them. what is the current in the solution
Beats of frequency 4Hz are heard when a tuning fork of frequency 1000Hz and a vibrating wire are sounded together. What is frequency of the wire.
you take a 100 g uniform meter stick and hang 200 g on the 10 cm mark, where should you clamp the meter stick so that it is in balanace
Vectors A and B have scalar product -3.00 and their vector product has magnitude 9.00. What is the angle between these two vectors
During a thunderstorm the electric field at a certain point in the earth's atmosphere is 1.11 105 N/C, directed upward, Find the acceleration of a small piece of ice of mass1.08 10-4 g
An electron and a proton are each placed at rest in a uniform electric field of magnitude 546 N/C. Compute the speed of each particle 52 ns after being free.
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