Question

A V = 130-V battery is connected across two parallel metal plates of area 28.5 cm² and separation 8.20 mm. A beam of alpha particles (charge +2e, mass 6.64 times 10^-27 kg) is accelerated from rest through a potential difference of 1.70 kV and enters the region between the plates perpendicular to the electric field, as shown in the figure.(Figure 1)  

Part A What magnitude of magnetic field is needed so that the alpha particles emerge undeflected from between the plates?  

B = _________

Answer 1

Accelerating Voltage = V1=1.70 kV = 1700 V

Charge on alpha= q=3.2*10^-19 C

Mass = m =6.64*10^-27 kg

Kinetic energy = electric potential energy

(1/2)mv^2 = qV

v = sq rt [2qV/m]

The alpha particles will emerge undeflected from between the plates if magnetic force=elctric force

qvB =qE

E = Vo/d

B = E /v

B =(Vo/d) sq rt [m/2qV]

Here :d= 8.2x10^-3m

V₀=130V

V = 1700V

B =0.039165 T

B =3.9165*10^-2 T