The scene is conducted at night and this would add to the supernatural feel of the scene. Tension is created in te recap by Banquo and Macbeth regarding what they experienced with the witches and the strange prophesies they were given.
The main source of tension is of course Macbeth's vision of the dagger. This is not made real to the audience and we are as bewildered by this 'dagger of the mind' as Macbeth is. As the dagger begins to bleed the audience shares Macbeth's fear and trepidation of what is to come. Then we are disturebed by his final rhyming couplet which highlights Macbeth's fatal decision.
Hear it not, Duncan, for it is a knell
That summons thee to heaven, or to hell
Act 2 scene 2 is the murder scene. The tension is begun with Macbeth and his wife starting at every sound as they follow through with their plan.
Macbeth is concerned that he has already been condemned by God before the deed has been discovered-
But wherefore could not I pronounce “Amen”?
I had most need of blessing, and “Amen”
Stuck in my throat.
Lady macbeth attempts to calm him and distract him from his destructive imaginings and there is irony in her words.
These deeds must not be thought
After these ways; so, it will make us mad.
Macbeth is appalled at the amount of blood on his hands - both literally and metaphorically. We also see the tension rise in te fact that Macbeth instantly regrets his actions-
Wake Duncan with thy knocking! I would thou couldst!