A small gas laser of the type used in classrooms may radiate light at a power level of 2.0 mW. If the wavelength of the laser light is 642 nm,
how many photons does it emit per second? (c = 3.0 × 108 m/s, h = 6.626 × 10-34 J ? s)
6.5 × 1015
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Derive an expression for the geometric shape factor F1–2 for a rectangular surface A1, 1 by 20 m placed parallel to and centered 5 m above a 20-m-square surface A2.
GIVEN
• Rectangular surface A1 and square surface A2
• A1 is parallel to and centered 5 m above A2
• Dimensions of A1 = 1 m × 20 m
• A2 is 20 m square
FIND
• The shape factor F12
SKETCH
In the atoms of most materials the fields of individual electrons
A) cancel one another. B) partly align. C) completely align.
If 
= 6.0, 
= 5.0, and ? = 40°, determine the scalar product of the two vectors shown.
?
?
A. +19
B. +23
C. ?19
D. ?23
E. +30
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