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Creating rainbows, Batteries in the fridge, Settling coffee grounds

Q: What causes rainbows after it stops raining? --Brandon M., 8 years old, Albuquerque, NM

A: Light and water create rainbows. However, to see a rainbow, it must be raining in one part of the sky, the sun shining from the opposite part, and you must have your back to the sun . Then raindrops, like tiny prisms, scatter the white sunlight into brilliant colors--red, orange, yellow, green, blue, indigo, violet--and make a rainbow.

[Corel] A rainbow stretches within the mists of Victoria Falls, Zimbabwe

The drops bend the light to scatter it. Light slows when it goes through water and this causes its path to bend.

A skater experience s the same thing, when suddenly a skate hits a rough spot and that skate slows. The skater turns toward the slower skate.

Light bends in a similar way both when it enters and leaves the raindrop. Click for figures: Figure 2.

Some colors slow more than others and therefore bend more. Violet light, for example, travels slower than red. That separates the violet from red light.

The red light emerges at a 42-degree angle to the original white ray. The violet reappears at only 40 degrees. The raindrop has separated the white light into colors and then re-directed the colored light back towards you. That's why you see the rainbow.

Now suppose the raindrop that we have been discussing is directly in front of you and at an angle of 42 degrees up: the angle of red light. Figure 3. Then the red light from that drop hits your eye and you see red. The violet light from that drop, however, is higher (at 40 degrees) and misses your eye. Maybe it hits your hat and you don't see violet. How, then, do you see all the colors in the rainbow? And how do you see the whole bow and not just a single light?

In Figure 3, you are looking straight in front at 42 degrees to see the red light scattered by our raindrop but remember, there are lots of raindrops in the sky. Look to your right or left, but still at 42 degrees. You will see more red. In fact, you will see an arc of red all coming into your eye at 42 degrees.

Now look straight in front but up a little, at 40 degrees: you see violet from other drops. Again sweeping your eye to the right or left but at 40 degrees shows a bow of violet.

That's how all the colors form a grand bow stretching from horizon to horizon.

Further Surfing:

Unidata: What is a rainbow?

Q: Does putting a battery in the refrigerator lengthen its storage life? --Lanney A., Sandia Park, NM

A: Storage of batteries in a refrigerator "will not significantly prolong storage life," says Bob Milanese, Director of Technical Support of Duracell Batteries.

Heat can hurt the batteries but, unless the temperature constantly exceed 90 degrees for months at a time, cooling the batteries will have little effect.

Further Surfing:

Duracell: Frequently answered questions about batteries

Q: When I'm out camping, I boil coffee in a pot and then, to settle the grounds, I drop an egg shell in. Does adding the shell make any difference? --Bert G., Albuquerque, NM

A: You've been there: it's cold still. The sun fills the sky with subtle hues but hasn't risen yet. Your fire crackles and warms your hands as you push the coffee pot closer to the flame. Bacon sizzles and eggs bubble. Ah! The water boils. You spoon in coffee and pull the pot off the fire. You drop in an eggshell and watch the coffee settle.

"Does it do any good?" Asks Bert.

No. I asked various coffee experts:

"We have never heard of this before!" The Roast and Post Coffee Company asserts and asks where my reader discovered this idea.

"I think it is more a matter of waiting long enough for gravity," says Beth Heiliger, the Roastmaster at Sacred Grounds Organic Coffee Roasters, who has never tried the eggshell approach.

So I ran an experiment to answer the question. I boiled regular-perk coffee in two identical containers for five minutes, stirred both containers, and dropped an eggshell in one container but not in the other.

After two minutes of watching coffee grounds settle, I scooped one cup of coffee and grounds mixture from the top of each container (avoiding the grounds below) and poured them into two separate coffee filters. The coffee took forever draining through the filters. But finally the filters had nothing but grounds. Then I compared the amount of grounds captured by each filter. I could not detect any difference.

(Answered Sep. 20, 2002)