How has life in Ember changed since the seven-minute power outage?

The seven-minute power outage is significant enough that it causes the community to come together and discuss what to do going forward about the increasing lack of power. However, the lack of actual effort toward finding a permanent solution makes the people of Ember angry—that's the change that occurs after the power outage.
Power outages are a fact of life in Ember, but when one lasts for seven minutes, it's not business-as-usual. It's twice as long as any outage that came before and puts people in a silent panic. Unlike the past outages where people would talk about the time without power, no one seems inclined to discuss the seven-minute outage. DuPrau writes:

It was strange how people didn’t talk much about the blackout. Power failures usually aroused lively discussion, with clumps of people collecting on corners and saying to each other, "Where were you when it happened?" and "What’s the matter with the electricians, we should kick them out and get new ones," and that sort of thing. This time, it was just the opposite.

When everyone gathers to hear the mayor, the crowd is restless and seems almost on the verge of a riot. They can't hear him through the speaker and he doesn't offer any real solutions. At one point, Lina is even afraid that she'll be trampled. The people have reason to be upset: the mayor is keeping supplies back from the shortages for himself and others while not actively looking for a solution to benefit everyone.

Before that people have already experienced blackouts during daytime every once in a while. They have heard of rumors of power shortage, but most people are not too concerned about that and still believe that they can somehow cope with it and carry on with their normal lives. The seven-minute power outage causes great panic among the citizens of Ember, as it’s not only the longest one in history but also more than twice as long as any other outage before. It’s clear that the situation has been getting worse rapidly. People become more aware of the severity of the power shortage issue facing Ember and begin to fear that one day Ember may run out of power. Some people start to actively search for solutions.