What is the significance of the sign `psi^(2)` ?

What is the significance of the -ve sign in W = -mgd?

Define Poisson's ratio.Write an expression for it. What is the significance of negative sign in this expression ?

Define Poisson's ratio. Write an expression for it. What is the significance of negative sign in this expression ?

The expression for the induced e.m.f. contains a negative sign [e=-(dphi)/(dt)] . What is the significance of the negative sign?

The total energy of the electron in an hydrogen atom is En = -13.6/n^2 eV What is the significance of the negative sign?

For a wave propagating in the positive x direction the instantaneous displacement of the particle is y=A sin ""(2pi)/T (t-x/v) . What is the significance of the negative sign ? If positive sign is used, what does it represent?

What is the significance of Psi and Psi^2 in the quantum mechanical model of atom?