About how old was the universe when the microwave background radiation that Penzias and Wilson discovered first became visible?
a. 1 microsecond (10^-6 second) when the electromagnetic force separated out from the electroweak force.
b. 3 minutes, the start of the period that ended with typical photons unable to produce electron-positron pairs.
c. 300 thousand years, when matter in the universe became transparent to photons.
d. 1 million years, when the strong force separated out.
e. 30 million years, when the strong force separated out.
c
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A long straight wire (diameter = 2.0 mm) carries a current of 30 A. What is the magnitude of the magnetic field 2.5 mm from the axis of the wire?
a. 3.2 mT b. 2.8 mT c. 2.4 mT d. 3.6 mT e. 3.0 mT
Emission lines of hydrogen that are found in the ultraviolet part of the electromagnetic spectrum are formed by electrons transitioning from:
A) any level to level 2. B) level 2 to any level. C) any level to level 1. D) level 1 to any level. E) any level to level 3.
As a guide, prepare a similar table showing the order of magnitudes of the thermal resistances of a unit area for convection between a surface and various fluids.
GIVEN • The order of magnitude of convective heat transfer coefficient ( h c) FIND • The order of magnitudes of the thermal resistance of a unit area (A Rc) SOLUTION The thermal resistance for convection is defined by Equation as
To determine the height of a flagpole, Abby throws a ball straight up and times it
She sees that the ball goes by the top of the pole after 0.50 s and then reaches the top of the pole again after a total elapsed time of 4.1 s. How high is the pole above the point where the ball was launched? (You can ignore air resistance.) A) 10 m B) 13 m C) 16 m D) 18 m E) 26 m