Question

The magnitude of electric field intensity that balances the weight of an $\alpha$-particle is
[Take, mass of proton, $m_p=1.67 \times 10^{-27} \,kg$, $g=10\, m / s ^2$ and $e=1.6 \times 10^{-19} C$ ]

• A. $3.3 \times 10^{-6} N / C$
• B. $4.2 \times 10^{-8} N / C$
• C. $2.5 \times 10^{-9} N / C$
• D. $2.1 \times 10^{-7} N / C$

Answer 1

Answer: (D)

For equilibrium of $\alpha$-particle,
$ q E=m g $
$ \Rightarrow E=\frac{m g}{q} $
$ =\frac{4 m_p \cdot g}{2 e}=\frac{4 \times 167 \times 10^{-27} \times 10}{2 \times 1.6 \times 10^{-19}} $
$ =2.1 \times 10^{-7} N / C$