NEET 2025 Physics Motion of Charged Particles MCQ Question

🧠 Explanation

For the electron to not deflect, the electric and magnetic forces must be equal and opposite:

$$qE=qvB$$

Therefore,

$$E=vB$$

Given:

$$v=\frac{c}{100}=\frac{3\times10^8}{100} =3\times10^6\ \text{m/s}$$

and

$$B=9\times10^{-4}\ \text{T}$$

So,

$$E=(3\times10^6)(9\times10^{-4})$$ $$\boxed{E=27\times10^2\ \text{V/m}}$$

Since the electric force must oppose the magnetic force, $\vec E$ is perpendicular to $\vec B$.

✅ Answer: (B)

$$\boxed{\vec E\perp\vec B,\quad E=27\times10^2\ \text{V/m}}$$

⚡ Quick Trick:

$$\boxed{E=vB}$$

For no deflection → electric force = magnetic force.