What is wrong with select?

[Robert A. Rawlinson]

I am trying to get the index for a state and when I do:
my $sql1 = "SELECT id, name_short, name_long FROM states WHERE 
name_short='PA";
$sth1 = $dbh->prepare($sql1);
#
$sth1->execute();

It works. But when I do:
$StateProvince = 'PA';
my $sql1 = "SELECT id, name_short, name_long FROM states WHERE 
name_short=$StateProvince";
$sth1 = $dbh->prepare($sql1);
#
$sth1->execute();

I get a message that:
DBD::mysql::st execute failed: Unknown column 'PA' in 'where clause' at 
TestDBI.pl line 14.

It seems to me this should work. I am new at this so I must have done 
something wrong, but what?
Thanks for any help you can offer.
Bob Rawlinson