Question of the Week

B R Sitaram

Here are the answers to last month’s questions!

Q 1. When a solar eclipse takes place, only very few places on Earth can see it and people travel hundreds of kilometres to see it. However more than half the Earth can see a lunar eclipse. How come?
A. The most common answer to this question is that the Earth is much larger than the moon, hence its shadow is much larger than that of the moon. However, the correct answer is simpler. Recall what happens when you are walking on a road during daytime. There is a tree near you which is casting a shadow on the road. Now, if you can see the road, you will be able to see the shadow! On the other hand, if you want to stop seeing the sun, you have to stand in the shadow! The same thing happens with a solar and a lunar eclipse. To see a solar eclipse, you have to be within the shadow cast by the moon. To see a lunar eclipse, on the other hand, all you need to be able to do is see the moon! At any given time one half of the Earth can see the moon; because a lunar eclipse can last for a long time (up to 2 hours) more than 50% of the Earth can witness it!

Q 2. Many photocopying machines, those that can enlarge an image while copying, have a setting for 142%. Why 142? Why not 150 or 200?
A. This actually has to do with the way metric paper sizes are defined. The idea is very simple: if you take any metric size (say A4) and divide the paper into two along the longer side, you get the next metric size, A5. Similarly, putting two A4 size papers side by side gives you A3. Now, consider a picture that is exactly A4 in size. When you reduce the picture to exactly fit into A5, you do not want the image to be distorted in any way. This tells us that the two rectangles, A4 and A5, must be similar to one another; the ratio of the sides of the A4 rectangle (or paper) must be the same as that of A5. This, along with the fact that A5 is half an A4 tells us that the ratio of the sides must be square root of 2, which is about 1.42! So, if you want to enlarge an A4 to A3, you must enlarge each side by the square root of 2, or 142%.

Q 3. Why are many packed food items like wafers sold in 28 g packs? Why not 25? Why not 30?
A. Most of these packed items use machinery imported from the US. The standard unit of measurement of mass there is the ounce, which is about 28 grams!

Q 4. What time of the day is right for having dinner? Morning, afternoon or night?
A. The surprising answer is, anytime of the day! Dinner is the main meal of the day and can be had at midday. The other meal names (breakfast, lunch, supper) are associated with fixed times of the day, but not dinner! In fact it was quite common for an English family to have a heavy dinner on Sunday afternoons, following it with a light supper in the evening!

Questions for this month

  1. Which of the following is the most important cause of stomach ulcers?
    i. Eating spicy food
    ii. Drinking excessive coffee
    iii. Infection by a bacterium
    iv. Less exercise
    v. Excessive use of oil
  2. In 1828, the German chemist Friedrich Wohler synthesized urea. Why is this considered to be such an important event in the history of science?
  3. Worcester, Leicester, Cholmondeley and Warwick are names of cities in England. In addition to this, however, these cities have something else in common. What is it? Hint: it has to do with the names of the cities.
  4. Epimendes, the Cretan, said “All Cretans are liars”. Why is this statement so important in logic?

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