First, the revelation of the Inspector's true identity as a police inspector investigating the death of a young woman named Eva Smith is a shocking twist that the audience does not see coming. This sudden change in the tone and direction of the play disrupts the audience's expectations and creates a sense of uncertainty.
Second, the Inspector's interrogation of the Birling family members exposes the dark secrets and moral failings of each character. The audience is made aware of the web of lies and deception that the Birlings have been living in, and they begin to question the morality and values of the characters. This revelation creates a sense of unease and discomfort among the audience, forcing them to confront their own moral compass and the consequences of their actions.
Third, the Inspector's investigation highlights the social inequalities and injustices that exist within the society portrayed in the play. The audience is confronted with the stark contrast between the Birlings' privileged lifestyle and the poverty and suffering of Eva Smith. This contrast prompts the audience to reflect on the broader societal issues and class divisions of the time, and to consider their own responsibility and compassion towards others.
Overall, the end of Act One in "An Inspector Calls" creates a powerful dramatic impact on the audience, leaving them in a state of shock, confusion, and contemplation. It sets the stage for the rest of the play, as the Birlings and the audience are forced to confront the consequences of their actions and come to terms with the moral dilemmas presented in the play.