The radiocarbon content of 14C decreases after the death of a living system with a half-life of 5730 y. If an archaeologist working a dig finds an ancient firepit containing some partially consumed firewood and the wood contains only 12.5 percent of the 14C content of an equal carbon sample from a present-day tree, what is the age of the ancient site?
17 190 years
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A) sound B) light C) radio D) all of the above E) none of the above
Starting from very far away, an object is moved closer and closer to a concave lens, eventually reaching the lens. What happens to its image formed by that lens? (There could be more than one correct choice.)
A) The image gets closer and closer to the lens. B) The image gets farther and farther from the lens. C) The image always remains virtual. D) The image eventually changes from real to virtual. E) The image keeps getting larger and larger.
Nichrome wire, often used for heating elements, has resistivity of 1.0 × 10-6 ? ? m at room temperature
What length of No. 30 wire (of diameter 0.250 mm) is needed to wind a resistor that has 50 ohms at room temperature? A) 22.4 m B) 0.61 m C) 6.54 m D) 3.66 m E) 2.45 m
A laser with a power of 1.0 mW has a beam radius of 1.0 mm. What is the peak value of the electric field in that beam?
A) 490 V/m B) 840 V/m C) 65 V/m D) 120 V/m E) 22 V/m