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Challenge Questions

Stop in and exercise your brain. Talk about this month's Challenge from Specs & Techs or similar puzzles.

So do you have a Challenge Question that could stump the community? Then submit the question with the "correct" answer and we'll post it. If it's really good, we may even roll it up to Specs & Techs. You'll be famous!

Answers to Challenge Questions appear by the last Tuesday of the month.

Pollination Puzzle: Newsletter Challenge (April 2018)

Posted March 31, 2018 5:01 PM
Pathfinder Tags: challenge question pollination

This month's Challenge Question: Specs & Techs from IEEE Engineering360:

During pollination – a life-or-death process without which our agricultural lands can become barren – bees move pollen from one flower and carry it to another. What is the exact procedure that makes this happen? How do the bees pull the pollen? With their mouth, with their wings, or using some other alternative? Explain.

And the answer is:

Bees do not pull pollen grains at all. The grains attach to the bee at the first flower, and then release from the bee at the second flower. This is an electrical process.

When the bee leaves the hive and travels through the air its body becomes positively charged. When hovering close to a flower, the electric field due to the positively charged bee produces an induced charge in some of the pollen grains that forces electrons in the grain to move closer to the positively charged bee, and the far side of the grain becomes positively charged. Because the negative side of the grain is closer to the positive bee, the grain is attracted and “jumps” to the bee, leaving the positive-charged side of the grains exposed to the environment.

Now we have a bee that is practically surrounded by positive charges. When the bee moves to the second flower it attracts electrons to the top of the stigma, making it a negatively charged object. The stigma, having a high concentration of negative charges, pulls the pollen grains and the grains jump to the stigma, pollinating the flower.

16 comments; last comment on 04/04/2018
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Core Conundrum: Newsletter Challenge (March 2018)

Posted February 28, 2018 5:01 PM
Pathfinder Tags: challenge question planet core

This month's Challenge Question: Specs & Techs from IEEE Engineering360:

A scientist claims she can determine the size and density of an extraterrestrial planet’s core by landing a spacecraft on its surface, using only radio equipment on the lander and corresponding equipment at tracking stations on Earth. How is this possible?

And the answer is:

A planet’s rotational motions, namely the precession rate of its spin axis and the nutation of its spin axis, depend on its interior structure. For this reason, a planet’s core size and density can be determined by estimations of its precession and nutation. The precession is the long-term drift of the planet’s rotation axis in space, while the nutation describes the periodic motions of this axis as observed from space.

The precession and nutation values can be ascertained based on measurements of the relative velocity of the lander and tracking stations on Earth. The relative velocity can be found by measuring the Doppler shift of radio transmissions sent from the tracking station to the lander and re-transmitted back to Earth.

NASA’s Mars InSight lander mission will carry out this very task through its Rotation and Interior Structure Experiment (RISE). The lander will be equipped with an X-Band radio transponder that will provide the radio link necessary for Doppler tracking of the lander’s location. From this information, Mars’ precession and nutation values can be calculated and the size and density of its core can be determined.

For more on the InSight mission, see this article.

7 comments; last comment on 03/02/2018
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Electric Bill Enigma: Newsletter Challenge (February 2018)

Posted January 31, 2018 5:01 PM

This month's Challenge Question: Specs & Techs from GlobalSpec:

A family moves into a new house in December and notices a musty smell in the basement and purchase a small dehumidifier. When the electric bill arrives a month later it is much higher than expected. The family compares it to their electrical usage at their old house and it is several hundred kWh more. The old owner confirms their bills were less as well. What is the issue?

And the answer is:

The new house has an electric hot water heater running continuously due to its having hot water heat. This is especially expensive in the winter. A leak is creating the musty smell in the basement. A quick call to a plumber resolves the issue and lowers future electric bills by several hundred dollars.

41 comments; last comment on 02/07/2018
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Fuddled Frequencies: Newsletter Challenge (January 2018)

Posted December 31, 2017 5:01 PM
Pathfinder Tags: challenge question frequency

This month's Challenge Question: Specs & Techs from GlobalSpec:

Suppose your preferred AM radio station is located at 800 kHz on your radio dial, and you have a very special, perfect radio receiver that can only tune exactly at 800 kHz, excluding all other frequencies. Would you hear the music more clearly using such a radio receiver, or there is no difference between it and a standard receiver? Can this be true if you have an FM receiver with the same characteristics?

And the answer is:

If the radio receiver is limited to exactly one frequency it cannot receive modulated waves, and without modulation no information can be transmitted – only hum. This is true for FM radios as well.

In order for a radio transmission to carry information (music in this case), the main signal (music) has to be modulated so it can make “different expressions.” AM waves are modulated by “adding” a high frequency (the carrier; this is the frequency at which you should tune your receiver) to the original signal (modulating signal). The result is a signal with highs and lows is shown in the figure.

The amplitude-modulated signal contains more than one frequency and the radio receiver must be able to receive all frequencies, including the frequency of the original signal.

176 comments; last comment on 01/23/2018
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Stumped by the Screen: Newsletter Challenge (December 2017)

Posted November 30, 2017 5:01 PM
Pathfinder Tags: challenge question lcd Screen

This month's Challenge Question: Specs & Techs from GlobalSpec:

Viewing a common LCD display from straight on, you see a figure in pink. Tilting the screen so that it is at a sharp angle in your field of vision, the figure appears to have changed to bright blue. Why has the apparent color of the figure changed?

And the answer is:

The apparent change in color of images on the screen is due to the structure of the LCD screen.

A liquid crystal display (LCD) monitor’s screen is composed of millions of elements known as pixels (picture elements). Each pixel is made up of three individual subpixels: red, green and blue. Each of these subpixels controls the amount of light that passes through them, regulating the amount of each color emitted by a pixel. The mixture of the three primary colors determines the final color that the eye perceives for a given pixel.

An LCD is comprised of layers of filters, liquid crystals, and transistors. For each subpixel, light emitted by a backlight passes through a polarizing glass filter, travels through twisted, nematic liquid crystals, and continues through another polarizing glass filter.

The first glass filter polarizes light so that all light waves except those vibrating horizontally are blocked. The light passes to the liquid crystal layer where all of the light vibrating horizontally passes through since the liquid crystals are by default twisted to the correct orientation to allow horizontally vibrating light to pass. The light then arrives at the second glass filter, which is structured to only allow light vibrating vertically to pass. Since all of the light at this point is vibrating horizontally, none of it can pass through the second filter, resulting in a dark subpixel.

To illuminate the same subpixel, all that is needed is to twist the liquid crystals to the appropriate orientation. This is accomplished through the use of transistors. Each of the subpixels is controlled by a transistor that switches on and off to control the flow of electricity through each of the liquid crystals. When liquid crystals have current flowing through them, they twist and rotate light waves passing through them by 90 degrees. Rotating the horizontally vibrating light by 90 degrees causes it to vibrate vertically, allowing it to pass through the second glass filter. The result is an illuminated subpixel. A color filter over each subpixel gives each element its color.

The reason the figure on the screen appears to change color is that by tilting the screen you are viewing light escaping before it has passed through the liquid crystals and polarizing filters in the same manner as it does from a face-on angle. Colors that would have been blocked are therefore able to leak through, resulting in the apparent change in color.

For more on how colors are displayed on computer monitors, see this article.

16 comments; last comment on 12/07/2017
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