原文已被隐藏，你可用 快捷键 - 或点击 显示原文 按钮来查看原文
1 .<-NARRATOR:->Listen to part of a lecture in a materials science class.
1 .<-MALE PROFESSOR:->So what's the first thing that comes to mind when we talk about uses for copper? Tammy?
1 .<-FEMALE STUDENT:->The penny? It's made of copper...
1 .<-MALE PROFESSOR:->Okay, good one... but what's a one-cent coin worth these days?
2 .You might get back change, like if you go to the store and give the cashier five dollars for something that costs four dollars ninety-eight cents, you'll get two cents back... but two cents doesn't buy much.
3 .The value of the penny in terms of what it'll buy has gotten so low that there's actually a move afoot to eliminate the coin from U.S. currency.
1 .But there's more to it. As Tammy implied, the penny looks like it's solid copper.
2 .It's reddish orange, with a bright metallic luster when it's new; but that's just the copper plating.
3 .The penny's not solid copper; in actuality, it's almost 98 percent zinc.
4 .But, um, given the rising value of both these metals, each penny now costs about 1.7 cents to produce... so it generates what's called negative seigniorage.
1 .Negative seigniorage is when the cost of minting a coin is more than the coin's face value.
2 .Even though the penny generates quite a bit of negative seigniorage, there's concern that if it is eliminated, we'll need more nickels— because more merchants might start setting prices in five-cent increments... four dollars ninety-five cents, and so on.
3 .So we need a trusty five-cent piece that can be minted economically.
4 .But the nickel's negative seigniorage is even worse than the penny's... each nickel costs the U.S. Mint ten cents to produce!
1 .Also, some of us are pretty attached to pennies for whatever reason... nostalgia, and then there's collectors... and people, if they see a penny on the sidewalk, they'll pick it up and think, "It's my lucky day."
1 .Another scenario is that without pennies, merchants, instead of charging four-ninety-eight, might round up the price to an even five dollars.
2 .So consumer goods would become slightly more expensive.
3 .But, on the other hand, some cash transactions would be more convenient for consumers.
4 .And, as I said, the government would save money if pennies were eliminated.
1 .<-FEMALE STUDENT:->But wouldn't the copper industry suffer financially if the U.S. government stopped buying copper to make pennies?
1 .<-MALE PROFESSOR:->[Leadingly, trying to get the student to see her mistake] But how much copper do pennies actually contain?
1 .<-FEMALE STUDENT:->[repeating the question to herself] How much... [realizing her mistake] Oh, got it... right.
1 .<-MALE PROFESSOR:->So, what else comes to mind when you think about copper? [beat—no takers] What else is copper used for?
1 .<-FEMALE STUDENT:->I know that copper can be shaped into all sorts of things: sheets... tubing... My cousin's house has a copper roof.
1 .<-MALE PROFESSOR:->Yes, like gold and silver, copper's extremely malleable, but it's not a precious metal; it's far less expensive than gold or silver.
2 .It's also a superb conductor of electricity, so you can stretch it into wires, which go into appliances and even car motors.
1 .Copper also has superior alloying properties—[clarifying] it's, y'know, when it's combined with other metals.
2 .For instance, how many of you play a brass instrument, like a trumpet or trombone?
3 .Well, brass is an alloy of copper and zinc. If your trombone was made of pure copper or pure zinc, it wouldn't sound nearly as beautiful as a brass trombone.
1 .Another alloy, a combination of copper and nickel, resists corrosion... it doesn't rust, even with prolonged exposure to water.
1 .<-FEMALE STUDENT:->But what about the Statue of Liberty, in New York Harbor? It's made of pure copper, but it turned green. Isn't that a sign of corrosion?
1 .<-MALE PROFESSOR:->Indirectly. If copper's exposed to damp air, its color changes from reddish orange to reddish brown.
2 .But, in time, a green film called a "patina" forms, and the patina actually serves to halt any further corrosion.
3 .It's one reason that ship hulls are made of copper-nickel alloys.
4 .These alloys are also hard for barnacles to stick to. If these little shellfish adhere to the hull of a ship, it produces drag, slowing the vessel down.
1 .Copper's also a key material used in solar-heating units and in water-desalination plants, which are playing increasingly important roles in society.
1 .Bottom line? If you're a copper miner, you won't lose any sleep should the penny get—if you'll excuse the expression—pinched out of existence.