Suppose electrons move through a copper wire at speed v. Call the linear charge densities in the Earth reference frame Ep for the fixed

Suppose electrons move through a copper wire at speed v. Call the linear charge densities in the Earth reference frame λ_Ep for the fixed positive ions in the wire and λ_En for the (negative) electrons. Observer E in the Earth reference frame (which is also the reference frame of the positive ions) measures the wire to be electrically neutral. Observer M is moving along with the electrons (in the same direction as the electrons and at speed v).

A) Calculate the linear charge density of the wire as measured by M in terms of λ_En if the speed is 4.5 ×105m/s. λ_M / λ_En = ?

B) Calculate the linear charge density of the wire as measured by M in terms of λ_En if the speed is 7.5 mm/s (an achievable speed for electrons in copper wire). λ_M / λ_En = ?