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M9L1

}Summary In this lesson, you were introduced to Coulomb's Law describing the forces between charged particles. Point charges are idealized point particles with no spatial extent. Coulomb's Law states that the magnitude, F of the electrostatic force exerted by one point charge on another point charge is directly proportional to the maghitudes g4 and g, of the charges and inversely proportional to the square of the distance r between them: f k'fl_?z where k is a proportionality constant 2 whose Sl unit is k = 8.99x10N-m2/C2. The electrostatic force is directed along the line joining the charges, and it is attractive if the charges have unlike signs and repulsive if the charges have like signs. When you rub ordinary objects, the charge produced is typically a microcoulomb (1 uC = 10 C) or less. In nature, large charges closer to the size of a coulomb can be found in lightning bolts where as much as 25 coulombs can be transferred between the cloud and the ground. The magnitude of the charge found on an electron or a proton is measured to be 1.602 x 1079 C. This charge is referred to as an elementary charge and is written as e = 1.602 x 109 C. We can determine the number of elementary charges found in one coulomb. 1C m = 6.24 x 10' elementary charges When Coulomb's law is written in the form f = kql_?z , the magnitude of the force can be found when the magnitudes of the two charges are given. The direction of the force is the line joining the two forces. If the two charges have the same sign, the force on one of the objects is directed away from the other object. If the two objects have opposite charges, the force on one is directed towards the other. Coulomb's Law f = k and Newton's Law of gravitation f GM are very similar. In both cases, the force depends on the inverse square L of the 2 2 2 r r distance between the two objects and is directed along the line between them. In addition, the force is proportional to the product of the magnitudes of the charges g4 and g5 in Coulomb's law and the masses m4 and m, in the gravitation law. However, the electrostatic force can be repulsive or attractive, whereas the gravitational force however is always an attractive force. Question(s): The physics of the DNA molecule. The two strands of the DNA molecule are held together by electrostatic forces. There are four bases which make up the DNA molecule, thymine (T), adenine (A), cytosine (C), and guanine (G). In two of the bases, thymine and adenine, an oxide ion with a single negative charge (O7) from the thymine base is attracted to a hydrogen ion (H*) from the adenine ion. The distance between the two ions is 28.0 nm. Note that the oxide ion has a charge equivalent to a negative elementary charge and the hydrogen ion is equivalent to a positive elementary charge. 1. What is the strength of the electrostatic force between these two ions? 2. What is the direction of the force exerted on the oxide ion by the hydrogen ion? (Assume that the oxide ion is to the right of the hydrogen ion.) 3. How many hydrogen ions would it take to equal the amount of charge contained in a lightning bolt, 25 coulombs