When a DNA molecule is in water, each base pair releases a pair of hydrogen ions. As a result, the DNA molecule has a net charge. Since there are a lot of base pairs in a string of DNA, this can be a lot of charge! On the web, find a reliable site (and be ready to say why you think it is reliable) that tells you the number of base pairs in a typical human chromosome. (Not the Y chromosome!) To get a sense of the total amount of charge involved, imagine that you had two coiled up chromosomes, each with a charge of 2 extra electrons per base pair. Suppose you held them fixed in a vacuum one micrometer apart. For simplicity, model the chromosomes as point charges.1) Estimate the electric force (in N) that the two chromosomes exert on each other in this situation. You may take the Coulomb constant to be kC ~ 9 × 109 N-m2/C2.2) Explain why you found the site you used in part (a) reliable and why this kind of electrostatic repulsion is not a problem when DNA is in its natural environment

Global warming will produce rising sea levels partly due to melting ice caps but also due to the expansion of water as average ocean temperatures rise. to get some idea of the size of this effect, calculate the change in length of a column of water 1.00 km high for a temperature increase of 1.00ºc. note that this calculation is only approximate because ocean warming is not uniform with depth. (answer in ×10^{-3} −3 m)

You are still fascinated by the process of inkjet printing, as described in the opening storyline for this chapter. you convince your father to take you to his manufacturing facility to see the machines that print expiration dates on eggs. you strike up a conversation with the technician operating the machine. he tells you that the ink drops are created using a piezoelectric crystal, acoustic waves, and the plateau-rayleigh instability, which creates uniform drops of mass m = 1.25 ✕ 10−8 g. while you don't understand the fancy words, you do recognize mass! the technician also tells you that the drops are charged to a controllable value of q and then projected vertically downward between parallel deflecting plates at a constant terminal speed of 20.0 m/s. the plates are ℓ = 2.15 cm long and have a uniform electric field of magnitude e = 6.40 ✕ 104 n/c between them. noting your interest in the process, the technician asks you, "if the position on the egg at which the drop is to be deposited requires that its deflection at the bottom end of the plates be 0.17 mm, what is the required charge on the drop (in c)? " you quickly get to work to find the answer. (neglect the force of gravity.)

Does a energy transformation happen when you drop your pencil