How Does Radioactivity Relate to the Number of Atoms in a Graph?

[ehabmozart]

What would be the shape of an "Activity versus Number of Atoms present" graph look like... We know that A=-λN ... They are propotional but there is a negative sign.. What would be the graph?? Thanks in advance!

 

[mfb]

Activity is proportional to the number of atoms with a positive constant.

 

[jtbell]

We know that A=-λN ... They are propotional but there is a negative sign.

Maybe your book does it differently, but to me, activity is a positive quantity so A = λN. Over time, the number of undecayed atoms decreases at a rate that equals the (negative of the) activity, and this is where the minus sign comes in: dN/dt = -A = -λN.