What is a disadvantage of having lots of turns in an elctromagnet

Who was the first scientist to measure speed as distance over time?

What properties of a moving object are used in determining the object's energy of motion

The charge on an electron is 1.60218 × 10−19 c and its mass is 9.10939 × 10−31 kg. how strong a magnetic field must be experienced by the electron if its path is a circle of radius 5.5 cm? answer in units of t.