Question

If mass of the electron $=9.1\times {10}^{-31}\text{kg}$, charge on the electron $=1.6\times {10}^{-19}\text{C}$ and $g=9.8{\text{ms}}^{-2}$. Then, the intensity of the electric field required to balance the weight of an electron is -

• A. $5.6\times {10}^{-9}\text{N/C}$
• B. $5.6\times {10}^{-11}\text{N/C}$
• C. $5.6\times {10}^{-8}\text{N/C}$
• D. $5.6\times {10}^{-7}\text{N/C}$

Answer 1

The correct option is B $5.6\times {10}^{-11}\text{N/C}$

From equilibrium of forces,

$qE=mg$

$\Rightarrow E=\frac{mg}{q}$

$\Rightarrow E=\frac{9.1\times {10}^{-31}\times 9.8}{1.6\times {10}^{-19}}$

$\Rightarrow E=5.6\times {10}^{-11}\text{N/C}$