In the Fourier heat equation we have dT/dt = alpha * (d^2T/dx^2), with alpha being the proportionality constant. What I do understand is the relation between derivatives of x and t, but why the proportionality constant? How does it even make sense?

Sawyer is studying diffraction. he draws a diagram of a plane wave to show how light waves travel. which best describes sawyer’s error? the wave fronts should be perpendicular to the direction in which the waves move. the arrow showing the direction of movement of the waves should be pointing to the left. the arrow showing the direction of movement of the waves should be pointing downward. the wave fronts should be both parallel and perpendicular to the direction in which the waves move.