If I set a calendar time while I am in one location, will the time change if I move the computer/iPhone/iPad to another time zone? How do I prevent this?

The iPhone may update its current time if its set to use the cellular service provider as a time source in Settings->General->Date & Time->Set Automatically.

The iPad and Computer, will probably not change the time automatically, but you can prevent it in Settings->General->Date & Time on the iPad and if the computer is a Mac, in System->Preferences->Date & Time->Set time Automatically.

With that said, if you added the event in calendar with a specific time zone, it will calculate the correct time for it in any other time zone you may be in. It should not be an issue if you change locations, the time will remain correct in relation to when you set it.

So if you set it to say 10am eastern, and you are now in a Pacific Time Zone, it will be re-calculated to 7AM Pacific. Rather than alerting you at 10am Pacific time.

That makes no sense. Because if you are in a place where they are 3 hours ahead for example, then you'll miss whatever appointment you had or event you needed to be reminded off. If it notifies you at 10am for something that already happened at 7am where you are.

That is, the time in relation to where you are will be wrong, so you'll either be late to the event or be too early. Either way, its not a good thing.

Either way the time shown in the calendar event will reflect the original time and timezone you set it to it will not change in the event details at all, but may show the time in the timezone it detects you are in.

The relative time it notifies you of the event will be related to the actual time set for the device.

As said, you can turn off the Automatic time changing based on zone in Settings on iOS and iPadOS devices and System Preferences on Mac.