Your roommate is having trouble understanding why solids form. He asks, “Why would atoms bond into solids rather than just floating freely with respect to each other?” To help him understand at least one type of bonding in solids, you decide to embark on an energy explanation. You show him a drawing of a primitive cell of a sodium chloride crystal, NaCl, or simple table salt. The drawing is shown in Figure P24.10, where the orange spheres are Na+ ions and the blue spheres are Cl− ions. Each ion has a charge of magnitude equal to the elementary charge e. The ions lie on the comers of a cube of side d. You explain to your roommate that the electrical potential energy is defined as zero when all eight charges are infinitely far apart from each other. Then you bring them together to form the crystal structure shown. (a) Evaluate the electric potential energy of the crystal as shown and (b) show that it is energetically favorable for such crystals to form.
Figure P24.10
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Chapter 24 Solutions
Physics for Scientists and Engineers
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- Suppose a capacitor consists of two coaxial thin cylindrical conductors. The inner cylinder of radius ra has a charge of +Q, while the outer cylinder of radius rb has charge -Q. The electric field E at a radial distance r from the central axis is given by the function: E = αe-r/a0 + β/r + b0 where alpha (α), beta (β), a0 and b0 are constants. Find an expression for its capacitance. First, let us derive the potential difference Vab between the two conductors. The potential difference is related to the electric field by: First, let us derive the potential difference Vab between the two conductors. The potential difference is related to the electric field by: Calculating the antiderivative or indefinite integral , Vab = (-αa0e-r/a0 + β + b0 ) By definition, the capacitance C is related to the charge and potential difference by: C = / Evaluating with the upper and lower limits of integration for Vab, then simplifying: C = Q / ( (e-rb/a0 - e-ra/a0) + β ln() + b0 () )arrow_forwardSuppose a capacitor consists of two coaxial thin cylindrical conductors. The inner cylinder of radius ra has a charge of +Q, while the outer cylinder of radius rb has charge -Q. The electric field E at a radial distance r from the central axis is given by the function: E = αe-r/a0 + β/r + b0 where alpha (α), beta (β), a0 and b0 are constants. Find an expression for its capacitance.arrow_forward23.57 - An Ionic Crystal. Figure P23.57 Figure P23.57 shows eight point charges arranged at the comers of a cube with sides of length d. The values of the charges are +q and -q, as shown. This is +9 a model of one cell of a cubic ionic crystal. In sodium chloride (NaCI), for instance, the posi- tive ions are Na* and the nega- tive ions are CI". (a) Calculate the potential energy U of this arrangement. (Take as zero the potential energy of the eight charges when they are infinitely far apart.) (b) In part (a), you should have found that U < 0. Explain the relationship between this result and the observation that such ionic crystals exist in nature.arrow_forward
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