CHEM106: Assessment 4 Wave Functions and Probability Answer Key 1. Define the complex conjugate of the following functions. The complex conjugate for a complex number Z = a + ib is defined as Z* = a ib. In general, to find the complex conjugate of any function, all we need to do is to reverse the sign of the imaginary component. A. Z * 3 ib B. f * ( x ) eix C. f * ( x ) sin( 2 x ) , noticing that for a real function, f * ( x ) f ( x ) 2. What are the requirements for an acceptable wavefunction? Since 2 * represents the probability density for finding the particle, the wavefunction itself must meet the following requirements: (1) finite (or quadratically integrable); (2) single valued; and (3) continuous. 3. Which of the following is an acceptable wave function over the indicated interval? A. 1 with 0 x x 1 is not an acceptable wavefunction since it approaches infinity as x = 0. x B. 2cos(x) with -¥ £ x £ 0 2cos(x) is an acceptable wavefunction since it meets all three requirements listed in question 2 in the specified domain. C. e x with x e x is not an acceptable wavefunction since it approaches infinity as x approaches . 4. Which of the following functions are normalizable over the indicated intervals? Normalize those functions that can be normalized. (Hint: In normalizing wavefunctions, the integration is over all space in which the wave function is defined.) A. f ( ) e i 0 2 The function is finite everywhere, and thus normalizable. 2 Given M 2 2 0 0 0 1 . M the normalization constant is Thus, the normalized function is f N ( ) B. f ( x) e2 x 2 f * ( ) f ( )d e i e i d d 0 2 , 1 i e . 2 with x The function f ( x) e2 x is infinite at x , and thus not normalizable. 2 x ) with 0 x L L The function is finite everywhere, and thus normalizable. C. f ( x ) sin( L Given M 0 2 2 2 f ( x ) f ( x )d x sin( x ) sin( x )d x sin 2 ( x )d x , L L L 0 0 L L * look up the integration table, and find that sin 2 (x )d x Thus, M 1 L 4 x sin( x) 2 8 L The normalization constant is L 0 1 1 x sin( 2x ) . 2 4 L L 4 L [sin( L) sin( 0)] . 2 8 L 2 1 . M Thus, the normalized function is f N ( x ) 2 2 sin( x) . L L 5. Consider the following normalized wavefunction ( x ) 1 3 cos( x ) , for a oneL 2L dimensional system confined in the region L x L . A. Calculate the probability that the particle will be found in the region between x = 0 and x = L/2. L/2 L/2 1 3 P * ( x ) ( x )d x cos2 ( x )d x L 0 2L 0 Look up the integration table, and find that 1 1 2L 6 P [ x sin( x )] L 2 12 2L 0 L/2 Thus, 1 1 ( 1) 0.197 4 6 1 1 cos (x)d x 2 x 4 sin( 2x) . 2 1 L 2L 6 L { [sin( ) 0]} L 4 12 2L 2 . B. Determine the probability that the particle will not be located in the region between x = 0 and x = L/2. The probability in case B and that in case A above should add up to 100%. Thus, P = 1 0.197 = 0.803.