What is a electromagnet?

Spend time observing or thinking about events that involve matter and energy. which events can you explain? which events can’t you explain?

If a balloon is taken outside on a very cold day, what will occur?

Electromagnetic induction. a coil of wire contains n turns and has an electrical resistance r. the radius of each turn is a. initially, inside the coil there exists a uniform magnetic field of magnitude b0 parallel to the axis of the coil. the magnetic field is then reduced slowly. the current induced in the coil is i. how long does it take for the magnitude of the uniform field to drop to zero?