A 0.50-m long solenoid consists of 1 000 turns of copper wire wound with a 4.0 cm radius. When the current in the solenoid is 18 A, the magnetic field at a point 1.0 cm from the central axis of the solenoid is:

 B = 4.52 10⁻² T

Explanation:

A solenoid creates a magnetic field given by

         B = μ₀ n i

Let's look for the density of turns in the solenoid length

         n = N / l

         n = 1000 / 0.50

        n = 2000 turns / m

        B = 4π 10⁻⁷ 2000 18

        B = 4.52 10⁻² T

The magnetic field is uniform inside the solenoid

what experimental evidence led scientists to change from the previous model to this one?

a few of the positive particles aimed at a gold foil seemed to bounce back.

the colors of light emitted from heated atoms had very specific energies.

experiments with water vapor showed that elements combine in specific proportions.

cathode rays were bent in the same way whenever a magnet was brought near them.