Question

A magnetic field of $5\times {10}^{-4}T$ just balances a perpendicular electric field of $15kV/m$ in their effect on an electron beam passing through the two fields in a direction perpendicular to both of them. What is the speed of the electrons?

• A. $75m/s$
• B. $3\times {10}^{4}m/s$
• C. $7.5\times {10}^{4}m/s$
• D. $3\times {10}^{7}m/s$

Answer 1

The correct option is D $3\times {10}^{7}m/s$

The relation between electric field and magnetic field is the speed of light given by Maxwell's equations.......

Therefore ,

$E=c\times B$

where E is the electric field..

B is the magnetic field.....

c is the speed of light...

further solving the equations we get......

$c=\frac{E}{B}$

$c=\frac{15\times {10}^3}{5\times {10}^{-4}}$

$c=3\times {10}^3\times {10}^4$

$\to 3\times {10}^{-7}m/s$

hence option D is correct