Adjusted code

Markiyan Hirnyk — Fri, 13 Jan 2012 23:14:56 Z

Replacing ?= by ?:= and changing the definition of B(nu), we obtain (Your range assignment is unclear for me.)
>restart;
>B := nu->2*h*nu^3/(c^2*(exp(h*nu*/(T*k))-1)); #better way to determinate Planck's law
>h := 6.63*10^(-34);
>c := 3*10^8;
>k := 1.38*10^(-23);
>T := 3000;
>plot(B(nu), nu = 0.1e-2 .. 10);
>plot(B, 0.1e-2 .. 10);#alternative

Edit. Formula for B.

Appendix

Markiyan Hirnyk — Sat, 14 Jan 2012 00:34:30 Z

PS. Also see the output of

PPS. Sorry,

MaplePrimes - answers and comments on Question, Can you help me for solving this ...

Adjusted code

Appendix