do not have to go on a ship at nearly the speed of light to see the effects of relativity - can arise even in a car moving slowly. The lead-acid batteries that start most of the engines of the vehicles get about 80 percent of its voltage from relativity, according to a published theoretical work on 7 January in the journal Physical Review Letters. The relativistic effect comes from the fast-moving electrons in atoms of lead. Computer simulations also explain why the tin-acid batteries do not function well, despite the apparent similarities between the tin and lead.
electrons orbiting the atoms usually at much lower speeds than the light, so that relativistic effects are largely ignored when describing the atomic properties. But notable exceptions include the heavier elements of the periodic table. Electrons must obiter nearly the speed of light to counteract the powerful attraction of its large core. According to relativity, these high-energy electrons in some way act as though they have a larger mass, so its orbit must be reduced in size compared to slow electrons to maintain the same angular momentum. This contraction, which is more pronounced in the spherically symmetric s orbital of the heavy elements, explains why gold has a yellowish hue and mercury is liquid at room bodies1.
Previous work has studied the relativistic effects lead crystal structure, but little research has been done on the chemical properties of these chemicals. As Rajeev Ahuja, Uppsala University in Sweden and his colleagues decided to investigate the most ubiquitous of the chemistry of lead: the lead-acid batteries. This technology is 150 years old based on cells consisting of two plates - made of lead dioxide (PbO2) - immersed in sulfuric acid (H2SO4). Lead releases electrons to become lead sulfate (PbSO4), while the lead dioxide gains electrons and becomes lead sulfate. The combination of these two reactions results in a voltage difference of 2.1 volts between the two plates.
Although there are theoretical models of the lead-acid batteries, Ahuja and his colleagues are the first to derive one from the fundamental principles of physics. To find the cell voltage, the team calculated the energy difference between the electronic configurations of the reactants and products. As a problem of a physics textbook involving balls rolling down the hill, there was no need to simulate the details of the intermediate states, provided they could calculate the initial and final energies.
"The really tough part is to simulate sulfuric acid electrolyte," says team member Pekka Pyykkö University of Helsinki. To avoid this, the researchers figured that the reaction began not with acid, but with the creation of acid from SO3, which is easier to simulate. And then subtracted the energy for the creation of acid (known to previous measures) of the total. "Lighting" and "off" the parties relativistic models, the team found that relativity accounts for 1.7 volts in each cell, which means that 10 of the 12 volt car battery comes from relativistic effects .
Without relativity, the authors argue, would act as lead tin, which is just above the table periodic and has the same number of electrons (four) in their outermost orbitals p and. But at the heart of tin only 50 protons, compared with 82 of the lead, so that the relativistic contraction of the outermost s orbital is much lower. Additional simulations showed that a hypothetical tin-acid battery voltage insufficient to produce a practice that was because of tin dioxide with sufficient force to attract electrons. The relatively isolated tin orbital s does not provide a sufficiently deep energy well for electrons compared with lead, the team found. In the past, researchers had found only a qualitative understanding of why the tin-acid batteries were not working.
Ram Seshadri, University of California at Santa Barbara said that he hoped there would relativistic effects, but they were so dominant. "In the world of work, the ability to reliably simulate a device as complex as a lead-acid battery from (almost) the key principles, including all relativistic effects modeling is a triumph," says Seshadri.
electrons orbiting the atoms usually at much lower speeds than the light, so that relativistic effects are largely ignored when describing the atomic properties. But notable exceptions include the heavier elements of the periodic table. Electrons must obiter nearly the speed of light to counteract the powerful attraction of its large core. According to relativity, these high-energy electrons in some way act as though they have a larger mass, so its orbit must be reduced in size compared to slow electrons to maintain the same angular momentum. This contraction, which is more pronounced in the spherically symmetric s orbital of the heavy elements, explains why gold has a yellowish hue and mercury is liquid at room bodies1.
Previous work has studied the relativistic effects lead crystal structure, but little research has been done on the chemical properties of these chemicals. As Rajeev Ahuja, Uppsala University in Sweden and his colleagues decided to investigate the most ubiquitous of the chemistry of lead: the lead-acid batteries. This technology is 150 years old based on cells consisting of two plates - made of lead dioxide (PbO2) - immersed in sulfuric acid (H2SO4). Lead releases electrons to become lead sulfate (PbSO4), while the lead dioxide gains electrons and becomes lead sulfate. The combination of these two reactions results in a voltage difference of 2.1 volts between the two plates.
Although there are theoretical models of the lead-acid batteries, Ahuja and his colleagues are the first to derive one from the fundamental principles of physics. To find the cell voltage, the team calculated the energy difference between the electronic configurations of the reactants and products. As a problem of a physics textbook involving balls rolling down the hill, there was no need to simulate the details of the intermediate states, provided they could calculate the initial and final energies.
"The really tough part is to simulate sulfuric acid electrolyte," says team member Pekka Pyykkö University of Helsinki. To avoid this, the researchers figured that the reaction began not with acid, but with the creation of acid from SO3, which is easier to simulate. And then subtracted the energy for the creation of acid (known to previous measures) of the total. "Lighting" and "off" the parties relativistic models, the team found that relativity accounts for 1.7 volts in each cell, which means that 10 of the 12 volt car battery comes from relativistic effects .
Without relativity, the authors argue, would act as lead tin, which is just above the table periodic and has the same number of electrons (four) in their outermost orbitals p and. But at the heart of tin only 50 protons, compared with 82 of the lead, so that the relativistic contraction of the outermost s orbital is much lower. Additional simulations showed that a hypothetical tin-acid battery voltage insufficient to produce a practice that was because of tin dioxide with sufficient force to attract electrons. The relatively isolated tin orbital s does not provide a sufficiently deep energy well for electrons compared with lead, the team found. In the past, researchers had found only a qualitative understanding of why the tin-acid batteries were not working.
Ram Seshadri, University of California at Santa Barbara said that he hoped there would relativistic effects, but they were so dominant. "In the world of work, the ability to reliably simulate a device as complex as a lead-acid battery from (almost) the key principles, including all relativistic effects modeling is a triumph," says Seshadri.
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