Living cells “pump” singly ionized sodium ions, Na+, from the inside of the cell to the outside to maintain a membrane potential ∆Vmembrane = Vin - Vout = - 70 mV. It is called pumping because work must be done to move a positive ion from the negative inside of the cell to the positive outside, and it must go on continuously because sodium ions “leak” back through the cell wall by diffusion. a. How much work must be done to move one sodium ion from the inside of the cell to the outside? b. At rest, the human body uses energy at the rate of approximately 100 W to maintain basic metabolic functions. It has been estimated that 20% of this energy is used to operate the sodium pumps of the body. Estimate—to one significant figure—the number of sodium ions pumped per second.
The amount the work must be done to move one sodium ion is
The numbers of sodium ions are
The equation of the potential energy is
where q is the charge and V is the potential difference.
Applying all data in the above equation
Number of sodium ions= power required to pump sodium ions/ work done to move the sodium ions
One form of nuclear radiation, beta decay, occurs when a neutron changes into a proton, an electron, and a neutral particle called a neutrino: where is the symbol for a neutrino. When this change happens to a neutron within the nucleus of an atom, the proton remains behind in the nucleus while the electron and neutrino are ejected from the nucleus. The ejected electron is called a beta particle. One nucleus that exhibits beta decay is the isotope of hydrogen , called tritium, whose nucleus consists of one proton (making it hydrogen) and two neutrons (giving tritium an atomic mass ). Tritium is radioactive, and it decays to helium:
a. Is charge conserved in the beta decay process? Explain.
b. Why is the final product a helium atom? Explain.
c. The nuclei of both have radii of . With what minimum speed must the electron be ejected if it is to escape from the nucleus and not fall back?
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