An electron experiences no deflection if subjected to an electric field of $3.2\times {10}^5\text{\hspace{0.17em}V}/\text{m}$ and a magnetic induction of  $2.0\times {10}^{-3}\text{\hspace{0.17em}T}$. Both the fields are applied perpendicular to the path of electron and also to each other. If the electric field is removed, then the electron will revolve in an orbit of radius______(in metres) (mass of the electron $=9\times {10}^{-31}\text{\hspace{0.17em}kg}$)

Given
Electric field  $E=3.2\times {10}^5\text{\hspace{0.17em}V}/\text{m}$
Magnetic induction $=2.0\times {10}^{-3}\text{\hspace{0.17em}T}$
Mass of the electron $=9\times {10}^{-31}\text{\hspace{0.17em}kg}$
Initially we have 
$eE=eVB$ 
$V=\frac{E}{B}=\frac{3.2\times {10}^5}{2\times {10}^{-3}}=1.6\times {10}^8\text{\hspace{0.17em}m}/\text{s}$ 
When electric field is removed, electron will only be moving in the influence of magnetic field and it follows a circular motion with radius given as 
$r=\frac{mV}{eB}=\frac{9\times {10}^{-31}\times 1.6\times {10}^8}{1.6\times {10}^{-19}\times 2\times {10}^{-3}}$

$\Rightarrow r=\frac{9\times {10}^{-1}}{2}=0.45\text{\hspace{0.17em}m}$