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ENG045_HW3

# ENG045_HW3 - DATE DUE ENG45 homework set#3 1 Weak...

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DATE: October 16, 2011 DUE: October 21, 2011 ENG45, homework set #3. 1. Weak interactions. We can write the van der Waals’ interaction energy between two atoms separated by the distance r , in the following three ways V ( r ) = 4 E 1 parenleftBigg parenleftbigg σ 1 r parenrightbigg 12 - parenleftbigg σ 1 r parenrightbigg 6 parenrightBigg (1) = E 2 parenleftBigg parenleftbigg σ 2 r parenrightbigg 12 - 2 parenleftbigg σ 2 r parenrightbigg 6 parenrightBigg (2) = K R r 12 - K A r 6 (3) where E 1 and E 2 are energies, σ 1 and σ 2 are distances, and K A and K R are constants with units necessary for the equalities above. a. Determine the SI units of K R and K A such that expression (3) makes sense. b. Write the interatomic force F ( r ) associated with the energy expressed in the form (1). c. Write the interatomic force F ( r ) associated with the energy expressed in the form (2). d. Write the interatomic force F ( r ) associated with the energy expressed in the form (3).

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