Neutral Atoms Made to Act Like Electrically Charged Particles

Science Daily, Apr. 18, 2011

Reported in the journal Nature Physics, these synthetic electric fields make each atom in a gas act, individually, as if it were a charged particle, but collectively they remain neutral, uncharged particles. This dual personality will help researchers simulate and study fundamental electrical phenomena and may lead to a deeper understanding of exotic phenomena involving charged particles such as superconductivity, the flow of electricity without resistance, or the quantum Hall effect, used by NIST to create a standard of electrical resistance.

Some aspects of electricity are difficult to study because, although oppositely charged particles are attracted to one another, similarly charged particles are repelled by one another. To get around this, NIST physicist Ian Spielman and his colleagues realized that they could make atoms, which are typically electrically neutral, act as if they are charged particles in an electric field -- extending their earlier method for making neutral atoms act like charged particles in a magnetic field.

The researchers create their synthetic electric field in an ultracold gas of several hundred thousand rubidium atoms. Using lasers, the team alters the atoms' energy-momentum relationship. This had the effect of transferring a bit of the lasers' momentum to the atoms, causing them to move. The force on each atom is physically identical -- and mathematically equivalent -- to what a charged particle would feel in an electric field.

So while the neutral atoms each experience the force of this synthetic electric field individually, they do not repel each other as would true charged particles in an ordinary electric field. This is analogous to an experienced group of dancers all following the moves of their instructor without getting in each other's way.

According to Spielman, this work may enable scientists to study the Hall effect, a phenomenon where an electromagnetic field can cause charged particles traveling through a conductor to experience a sideways force, which has of yet been unobserved in cold-atom systems. The work may also facilitate measurements of the atomic equivalents of electrical quantities such as resistance and inductance. For neutral atoms in synthetic electric fields, inductance is a measure of the energy that is stored as a result of the atoms' motion, and resistance is a measure of the dissipation, or energy loss, in the system. Measuring these quantities could provide insights into the properties of charged particles in analogous systems, including superconductors.

Text 8

Practice 1. Choose the key sentence in each paragraph.

Practice 2. Re-read the text to find out the author’s main idea:

1. Dr. Pearce has created a calculator program available for download online that can be used to determine the true costs of solar energy.

2. Many analysts project a higher cost for solar photovoltaic energy because they don't consider recent technological advancements and price reductions.

3. Analysts look at many variables to determine the cost of solar photovoltaic systems for consumers

4. The public is being kept in the dark about the viability of solar photovoltaic energy.

Practice 3. Make a review of the text.

Solar Power Much Cheaper to Produce Than Most Analysts Realize, Study Finds

Science Daily,Dec. 8, 2011 .

"Many analysts project a higher cost for solar photovoltaic energy because they don't consider recent technological advancements and price reductions," says Joshua Pearce, Adjunct Professor, Department of Mechanical and Materials Engineering. "Older models for determining solar photovoltaic energy costs are too conservative."

Dr. Pearce believes solar photovoltaic systems are near the "tipping point" where they can produce energy for about the same price other traditional sources of energy.

Analysts look at many variables to determine the cost of solar photovoltaic systems for consumers, including installation and maintenance costs, finance charges, the system's life expectancy, and the amount of electricity it generates.

Dr. Pearce says some studies don't consider the 70 per cent reduction in the cost of solar panels since 2009 . Furthermore, he says research now shows the productivity of top-of-the-line solar panels only drops between 0.1 and 0.2 percent annually, which is much less than the one per cent used in many cost analyses.

Equipment costs are determined based on dollars per watt of electricity produced. One 2010 study estimated the this cost at $7.61, while a 2003 study set the amount at $4.16. According to Dr. Pearce, the real cost in 2011 is under $1 per watt for solar panels purchased in bulk on the global market, though he says system and installation costs vary widely.

Dr. Pearce has created a calculator program available for download online that can be used to determine the true costs of solar energy.

The Queen's study was co-authored by grad students Kadra Branker and Michael Pathak and published in the December edition of Renewable and Sustainable Energy Reviews.

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