A tightly sealed house has a large ceiling fan that blows air out of the house and into the attic. The owners turn the fan on and forget to open any windows or doors. What happens to the air pressure in the house after the fan has been on for a while, and does it become easier or harder for the fan to do its job

Assuming the attic is ventilated to the open air the air pressure inside the house gets lower and the fan job becomes easier. It will speed up because while the pressure differential across the fan is increased, the mass of air being moved has decreased.

This can be verified by running a household vacuum cleaner in hose mode. With the hose open and air moving through it, the motor speed will be at a certain level producing a certain noise pitch . Placing your hand over the hose end will decrease the pressure in the hose, reduce the volume of air moving and you will hear an increase in motor pitch as it speeds up under lower load conditions.

The area inside the vacuum hose is akin to the inside of a well sealed house with an attic fan running.

the minimum amperage that the current in this wire would have to have so that its weight is completely supported by the magnetic force due to earth's field, assuming that no other forces except gravity act on it