Hello!
The probability density is the square of the absolute value of a wave function, in our case it is P_d(x)=|Psi(x)|^2=c^2 e^(-2x/L) for positive x's and c^2 e^(2x/L) for negative x's.
The integral over the real axis of a probability density must be 1 (the total probability). From this statement we can find c:
int_(RR) p_d(x) dx = 2 int_0^(+oo) c^2 e^(-2x/L) dx = -2c^2 L/2e^(-2x/L) |_(x=0)^(+oo) = c^2 L=1.
So really c = 1/sqrt(L) approx 0.707. (b)
(c) the probability of finding the particle within 1 mm of the origin is the integral of the probability density from -1 to 1. It is evidently
2 int_0^1 1/L e^(-2x/L) dx = -2/L L/2e^(-2x/L) |_(x=0)^1 = 1-e^(-2/L) = 1-e^(-1) approx 0.632,
which is really 63.2%.
(a), (d) look at the graph at https://www.desmos.com/calculator/mmija615t1
You can click on the orange circles at the left to disable the shading.
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