Radiation: A giant star radiates energy at the rate of 3.0 × 1030 W, and its surface temperature has been measured to be 3000 K. Assuming that it is a perfect emitter, what is the radius of this star?(? = 5.67 × 10-8 W/m2 ? K4)
A. 7.8 × 1010 m
B. 8.7 × 1010 m
C. 1.4 × 1010 m
D. 1.9 × 1011 m
E. 2.3 × 1011 m
Answer: E
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If an electron is accelerated from rest through a potential difference of 100 V, what is its de Broglie wavelength?
A. 
B. 
C. 
D. 
E. 