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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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.
Diamond has an index of refraction of 2.419 . What is the critical angle for internal reflection inside a diamond that is in air?
a. 24.4° b. 48.8° c. 155° d. 131°
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