Adiode vacuum tube consists of a cathode and an anode spaced 5-mm apart. if 300 v are applied across the plates. what is the velocity of an electron midway between the electrodes and at the instant of striking the plate, if the electrons are emitted from the cathode with zero velocity?

Velocity of the electron mid way = v = 6.47×10⁶ m/s  

Explanation:

Electric potential varies with distance as

At a distance 5 mm , the constant C is evaluated.

C =

    =

     = 3.50×10⁵  

Now at the mid point, x = 2.5 mm = 0.0025 m

Potential = V' =

                      =

                      = 119 V

Kinetic energy per unit charge is equal to the electric potential.

or 0.5 m v^2 = V' q

Here m is the mass of the electron and q is the charge of the electron.

m= 9.1×10⁻³¹ kg

q = 1.6×10⁻¹⁹ coulombs

⇒

⇒

⇒ v = 6.47×10⁶ m/s

⇒ Velocity of the electron mid way = v = 6.47×10⁶ m/s    

a.metals can become magnetic if they have many spinning electrons that create magnetic fields.d.only some metals are attracted by magnets; these metals are called ferromagnetic.

d.wrapping an insulated wire around a metal with ferromagnetic properties and applying an electric current.