Questões de Concurso

The Disappearing Honeybee

• Honeybees do more than just make honey. They fly around and pollinate flowers, plants, and trees. Our fruits, nuts, and vegetables rely.....................these pollinators. One third.....................America’s food supply is pollinated.....................the honeybee.

Have you seen or heard a honeybee lately? Bees are mysteriously disappearing in many parts of the world. Most people don’t know about this problem. It is called “colony collapse disorder” (CCD). Some North American beekeepers lost 80% of their hives from 2006-2008. Bees in Italy and Australia are disappearing too.

The disappearance of the honeybee is a serious problem. Can you imagine never eating another blueberry? What about almonds and cherries? Without honeybees food prices will skyrocket. The poorest people always suffer the worst when there is a lack of food.

This problem affects other foods besides fresh produce. Imagine losing your favourite ice cream! Haagen Daaz is a famous ice cream company. Many of their flavours rely on the hard working honeybee. In 2008, Haagen Daaz began raising money for CCD. They also funded a garden at the University of California called The Haven. This garden helps raise awareness about the disappearing honeybee and teaches visitors how to plant for pollinators.

Donating money to research is the most important thing humans can do to save the honeybee. Some scientists blame CCD on climate change. Others think pesticides are killing the bees. Commercial bee migration may also cause CCD. Beekeepers transport their hives from place to place in order to pollinate plants year round.

https://www.englishclub.com/reading/environment/honeybee.htm

1. What is an analog-digital converter?

An Analog-Digital Converter (ADC) is a widely used electronic component that converts an analog electric signal (usually a voltage) into a digital representation. The ADCs are at the front-end of any digital circuit that needs to process signals coming from the exterior world. Its schematic symbol is:

The output of a microphone, the voltage at a photodiode or the signal of an accelerometer are examples of analog values that need to be converted so that a microprocessor can work with them.

2. How does the ADC convert a signal?

Many ways have been developed to convert an analog signal, each with its strengths and weaknesses. The choice of the ADC for a given application is usually defined by the requirements you have: if you need speed, use a fast ADC; if you need precision, use an accurate ADC; if you are constrained in space, use a compact ADC.

All ADCs work under the same principle: they need to convert a signal to a certain number of bits N. The sequence of bits represents the number and each bit has the double of the weight of the next, starting from the Most Significant Bit (MSB) up to the Least Significant Bit (LSB). In a nutshell, we want to find the sequence of bits bN−1, bN−2, ..., b0 that represents the analog value Vin as Vin=∑n=0N−1bn2nVref2N.

                                (www.onmyphd.com/?p=analog.digital.converter. Adaptado)