It’s like a snapshot in time for quantum mechanics.
Now, if you’ve ever tried to solve this equation before, you know it can be pretty tricky. But don’t freak out! We’re going to break it down into some simple steps that even your grandma could understand (well… maybe).
Step 1: Write the TISE in its most basic form. It looks like this:
Δψ(x) = Eψ(x), where Δ is the Laplacian operator and E is a constant energy value. This equation tells us that if we have some function, ψ(x), which describes how a particle behaves at position x, then its second derivative (the Laplacian) equals the product of itself with a constant number, E.
Step 2: Separate variables! This is where things get funky. We’re going to assume that our function can be written as the product of two separate functions, one for position and one for energy:
ψ(x) = X(x) * Y(E), where X(x) describes how the particle behaves at a specific position x, and Y(E) tells us about its behavior with respect to energy. This is called “separation of variables.”
Step 3: Plug in our new function into the TISE and separate it into two equations: one for X(x), and another for Y(E). The equation for X(x) looks like this:
ΔX(x) = -λX(x), where λ is a constant that depends on E. This tells us that if we have some function, X(x), which describes how the particle behaves at position x, then its second derivative (the Laplacian) equals minus lambda times itself.
Step 4: Solve for X(x). To do this, we’re going to assume that our function can be written as a product of two other functions, one for the x-axis and another for y-axis:
X(x) = A * sin(kx), where k is some constant. This tells us that if we have some function, X(x), which describes how the particle behaves at position x on the x-axis, then it can be written as a sine wave with an amplitude of A and a wavelength of 2π/k.
Step 5: Plug in our new function for X(x) into the equation from Step 3 to get:
ΔX(x) = -λX(x), where Δ is the Laplacian operator, which looks like this:
ΔX(x) = d^2X/dx^2. Plugging in our new function for X(x):
d^2[A * sin(kx)] / dx^2 = -λ[A * sin(kx)]. Simplifying, we get:
-k^2 A * sin(kx) = -λ A * sin(kx). Canceling out the common terms and rearranging gives us:
k^2 = λ. This tells us that if our function can be written as a sine wave, then its wavelength is directly related to the constant value of lambda (which depends on E), which in turn determines how much energy the particle has.
Step 6: Solve for Y(E). To do this, we’re going to assume that our function can be written as a product of two other functions, one for the x-axis and another for y-axis:
Y(E) = B * e^(-βE), where β is some constant. This tells us that if we have some function, Y(E), which describes how the particle behaves with respect to energy on the y-axis, then it can be written as an exponential decay function with an amplitude of B and a rate of decay determined by β.
Step 7: Plug in our new function for Y(E) into the equation from Step 3 to get:
ΔY(E) = 0, where Δ is the Laplacian operator, which looks like this:
ΔY(E) = d^2Y/dE^2. Plugging in our new function for Y(E):
d^2[B * e^(-βE)] / dE^2 = 0. Simplifying, we get:
0 = 0. This tells us that if our function can be written as an exponential decay function, then its second derivative with respect to energy is always zero (because it’s a constant).
Step 8: Putting it all together! We now have two separate functions for X(x) and Y(E), which we can plug into the original TISE equation from Step 1. This gives us:
ΔX(x) * Y(E) = E * X(x) * Y(E). Simplifying, we get:
-λX(x) * Y(E) = E * X(x) * Y(E), where -λ is the constant value of lambda that depends on E. Canceling out the common terms and rearranging gives us:
k^2 = λ = (2m/ħ^2)*E, where m is the mass of the particle, ħ is Planck’s constant divided by 2π, and E is its energy value. This tells us that if our function can be written as a sine wave with an exponential decay function, then its wavelength is directly related to the energy value of the particle (which in turn determines how much it costs to create or destroy).
Who said physics had to be boring?