Two very thin lenses, each with focal length 20. cm, are placed in contact. What is the focal length of this compound lens?
A) 15. cm
B) 10. cm
C) 30. cm
D) 40. cm
E) 20. cm
B
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Diamond has an index of refraction of 2.419 . What is the critical angle for internal reflection inside a diamond that is in air?
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What protects Earth from the high energy particles ejected from the Sun (the solar wind)?
a. the troposphere b. the stratosphere c. the exosphere d. the magnetosphere e. the Van Allen radiation belts
Star A has an apparent magnitude of 3 and Star B has an apparent magnitude of 5. Which star is brighter in our sky?
A) Star A B) Star B C) The two stars have the same brightness in our sky, but Star A is closer to us than Star B. D) There is not enough information to answer the question.
A wire (length = 2.0 m, diameter = 1.0 mm) has a resistance of 0.45?. What is the resistivity of the material used to make the wire?
a. 5.6 × 10^?7 ? / m b. 1.2 × 10^?7 ? / m c. 1.8 × 10^?7 ? / m d. 2.3 × 10^?7 ? / m e. 7.1 × 10^?7 ? / m