How to prove how many ireducible polynomials are in a polynomial ring over a finite field.

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Can someone help me out with some problem concerning the cardinaliy of ireducible polynomials in $(\mathbb Z/p\mathbb Z)[x]$?

Here first why the problem appeared,

I want to prove that $card(max(p\mathbb Z[x]))=\infty$ where $max(p\mathbb Z[x])$ denotes the set of all maximal ideals containing $p\mathbb Z[x]$ for some prime $p$. So I showed in a first step that $p\mathbb Z[x] + f\mathbb Z[x]$ is an maximal ideal iff $\pi(f)$ is an ireducible polynomial and where $\pi:\mathbb Z[x]\rightarrow(\mathbb Z/p\mathbb Z)[x]$ is the canonical projection.

If now there exists infinitely many ireducible polynomials in $(\mathbb Z/p\mathbb Z)[x]$ i could use the fact that $\pi$ is surjecive to conclude that $card(max(p\mathbb Z[x]))=\infty$ since $p\mathbb Z\subset p\mathbb Z[x] + f\mathbb Z[x] \;\;\forall f\in\mathbb Z[x]$.

But I am not even sure if there are...

Thanks