Physics 16 Pretest 4

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1. In general, if you go up to a metal chair in a room, it will feel cooler than a wooden chair, even if they are right next to each other. This is because:
metals are at a lower temperature than wood
metals conduct heat away from your hand faster than wood
metals are smoother than wood, and you misinterpret this as a difference in temperature
your skin chemically reacts with the wood so it feels hotter

2. Why does a helium balloon rise in air?
helium is at a higher pressure than the surrounding air and pushes up on the balloon
helium is hotter than the surrounding air and hot gas rises
helium is lighter than air and so the balloon floats like a cork in water
there are fewer atoms of helium per cubic meter in the balloon

3. Why do filaments in lightbulbs fail?
small amounts of water in the bulb rust the filament metal.
the atoms of the filament metal are used up in the flowing electrical current
the metal of the filament evaporates until the filament is too fragile
the flowing electrons knock out metal atoms and create breaks