General Science Part V Quiz | Sci / Tech

Quiz Answer Key and Fun Facts

1. Suppose you have a big petrol tank, made of iron, buried in your garden. It might be a good idea to protect it against corrosion, so the petrol will not end up in the soil of your garden. From the proposed answers, which one will be the most effective?

Answer: Block of Mg buried close to the tank, connected by a Cu-wire

First of all, when talking about corrosion, there is a ranking of metals. A metal that corrodes more slowly is called the 'noble' metal. Au (gold) is more noble and will not protect the iron at all, since the iron will corrode first. So the correct answer involves Mg (Magnesium).

When attached firmly to the tank, it will give a very good protection, though only locally at that position of the tank. By putting it next to the tank, it will protect the whole tank (better divided streamlines). By attaching an Amperemeter to the system, you'll be able to follow the reaction.

When the Mg is corroding, a small current will flow through the Cu-wire. When the current is Zero, the Mg has corroded completely and the Iron will start corroding next.

This could be spotted in an industrial area, you might find some small orange posts, containing amperemeters to follow up on the situation.

2. I have two identical glasses of fresh water at room temperature. In the first glass I dissolve two teaspoons of salt. Then I take two identical ice cubes and throw them in the glasses (one in each). Which ice cube will be melted first?

Answer: the one in the fresh water

The meltwater from the ice cube is cold and therefore heavier than the fresh water at room temperature. Hence the meltwater will go down in the glass, inducing a circulation in the glass of water. There will be a supply of fresh water at room temperature to the floating ice cube, causing it to melt quickly.

In the salty water, the meltwater is lighter than the salty water and it will stay on top of it. No circulation occurs, and the ice cube is floating on the meltwater that has a lower temperature than the room temperature.

Therefore it will melt more slowly in the salty water. Try this at home if you don't believe it ;-)

3. Staying with the ice cubes, I could propose a new trick to the world's greatest magicians. Take a piece of ice, shaped as a brick. Support it on both sides. Put a steel wire in a loop around it and fix a large iron cube on the loop (so you have a loop around the ice, with a big weight hanging under it). Abracadrabra, when you check after some time, the loop will have gone through the ice, without the ice being cut in two. (supposing the temperature in the room is not too high and the ice doesn't melt entirely before the end of the experiment of course). Is this possible?

Answer: Yes

This is known as the Tyndall experiment (1820-1893). Under the steel wire the ice feels a local high pressure. The melting point decreases under higher pressure (normally it situated at 0�C, under atmospheric pressure), so the ice under the wire melts.

The wire goes down through the water, and the water doesn't feel any pressure anymore. The melting of the next layer of ice under the wire requires a certain heat, that will be subtracted from the water above, allowing it to freeze again... Amazing no? But I'm afraid the experiment takes too long to be commercially exploited though :-)

4. As you probably know, an airplane has rubber tires underneath it. These tires are not filled with compressed air, like the tires from your car. The reason for this is, amongst others, the fact that the tires have to face a very big temperature difference after taking off. Do you know which gas is used to fill up the tires?

Answer: nitrogen

Nitrogen gas is very inert, what prevents corrosion of the steel cords in the tires. It has a very homogeneous composition preventing big expansions due to the high temperatures. Of all the gasses mentioned, it has the biggest molecules. This means that the diffusion of the gas through the rubber (the high pressure will enhance this phenomenon) will be much less than with the other gasses.

Besides airplane tires, you'll find also nitrogen in Formula One tires and tires of trucks.

5. Now for some factual knowledge. When talking about earthquakes, we all know the Richter Scale, that gives an indication about the strength of the earthquake. In the past, there was another scale that was used, do you know which one?

Answer: Scale of Mercalli

The other possibilities are made up. This scale looks mainly at the damage that occurred to classify an earthquake. So it's more a qualitative assessment than a quantitative assessment. Damage is also dependent on the area where it occurred. For instance, a small earthquake might be more harmful in a city than somewhere in the outback. So the Richter scale is a more 'neutral' scale, allowing it to compare different earthquakes more accurately...

Hope you enjoyed this quiz?

Source: Author wimm

This quiz was reviewed by FunTrivia editor crisw before going online.
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General Science Part V Trivia Quiz

Part five in the series. I hope it's not too tough. Have fun.

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