Muggles' Guide to Harry Potter/Magic/Crucio

Overview
Crucio, also known as the Cruciatus Curse, causes extreme amounts of pain on the victim. Along with the Imperius Curse and the Killing Curse, the Cruciatus Curse is considered to be one of the most terrible curses in the magical world, called the Unforgivable Curses; the use of any of the three on another human being is punishable by a life sentence in Azkaban.

Extended Description
Bellatrix Lestrange and three other of Lord Voldemort's Death Eaters used this curse on Neville Longbottom's parents, torturing them into a state of irreversible madness. Since that time, they have resided in a special ward at St. Mungo's Hospital.

Harry Potter attempts this curse on Bellatrix Lestrange after she kills Harry Potter's godfather, Sirius Black. However, when Harry casts this curse it does not have the same effect as Lestrange's or other Dark Wizards'. As Bellatrix explains to Harry, he has to mean it in order for the curse to have its desired effect. In Harry's case, he is consumed with a righteous anger rather than a malicious intent.

Draco Malfoy attempts to use this curse on Harry at one point, but is forestalled by Harry's use of Sectumsempra.

Harry uses this curse again on Amycus Carrow, who has just spat at Professor McGonagall. The curse is much more effective this time, as Harry feels hatred towards Carrow.

It hardly needs to be mentioned that this is one of Voldemort's favorite spells. Voldemort uses this spell on his own followers numerous times as punishment, and twice uses it on Harry. The second time, it is ineffective, because the wand he is using has chosen Harry as its master.

Analysis
Neville's parents and their spell-caused insanity prove to be a plot point. Because of his parents' permanent incapacity, Neville is raised by his grandmother, and ends up very uncertain of his own magical ability. Once he comes into his strength, however, he seems to be adamant that what befell his parents will not be his own fate. Whether this is the reason he is able to destroy Nagini, Voldemort's pet snake and final Horcrux, is never definitively stated, but we feel that without the strength Neville found within himself as a result of his parents' fate, Neville would not have been able to act.

Questions

 * 1) Why was Voldemort's Cruciatus Curse ineffective against Harry in the Forbidden Forest after Harry's "near-death" experience?
 * 2) Does the wand in any way define the power of the Cruciatus curse?

Greater Picture
In Harry Potter and the Order of the Phoenix, Harry attempts to use the Cruciatus Curse against Bellatrix Lestrange, in self-defense, but fails. Bellatrix taunts him for this failure, and tells Harry he has "to really mean it", that he has to really hate someone for that curse to be effective. Just as the Patronus charm depends upon having a mind filled with happy thoughts, so must the Unforgivable Curses depend on having the mind filled with unrighteousness hate or anger. Harry truly realizes this when he casts the Cruciatus Curse on Amycus Carrow after Carrow spits in the face of Professor McGonagall in the Ravenclaw dormitory, stating his understanding of the anger one must feel to make such a curse be effective.