Critical Hits & magic

[DMSpelD]

i understand the Critical hit rules for normal attacks, but I don't understand how you can get a critical Hit on a spell.
Were are those rules in the rulebooks? When do I need to make an attack role when I am casting a spell?
I have found a text about what spells are attacks (page 208 of the Core Rulebook), but it does not say anything about making an attack roll.

[DeathMvp]

Any spell that forced you to roll a attack (rays and touch spells mostly) if you roll a nat 20 on them you crit for x2. Mind you other things can change this like the Magus though.

[Jeraa]

When a spell requires an attack roll, it specifically says so. Usually a melee touch attack or a ranged touch attack. Area spells don't require and attack roll, and so can't critically hit.

Quote:

You fire a small orb of acid at the target. You must succeed on a ranged touch attack to hit your target. The orb deals 1d3 points of acid damage. This acid disappears after 1 round.

Quote:

Your successful melee touch attack deals 1d6 points of electricity damage per caster level (maximum 5d6). When delivering the jolt, you gain a +3 bonus on attack rolls if the opponent is wearing metal armor (or is carrying a metal weapon or is made of metal).

[dragonhunterq]

Specifically check out the CRB chapter 9 page213 the section on touch range and page 214 look at rays under the 'effects' banner

[DMSpelD]

Thank you.

[BretI]

Also CRB pg. 184 at the end of the section about critical hits -- just above Activate Magic Item -- specifically says any spell that requires an attack roll.