An electron moving towards the east enters a magnetic field directed towards the north. The force on the electron will be directed

Options

A. Vertically upward
B. Vertically downward
C. Towards the west
D. Towards the south

Answer

To determine the direction of the force acting on an electron moving in a magnetic field, we can use the right-hand rule and the formula for the magnetic force on a charged particle.

### Step-by-Step Solution:

1. **Identify the Directions**:
- The electron is moving towards the east. We can denote this direction as the positive x-direction.
- The magnetic field is directed towards the north, which we can denote as the positive y-direction.

2. **Use the Right-Hand Rule**:
- According to the right-hand rule, if you point your thumb in the direction of the velocity (V) of the charged particle (the electron in this case), and your fingers in the direction of the magnetic field (B), then your palm will face in the direction of the force (F) acting on a positive charge.

3. **Determine the Force Direction**:
- For an electron, which has a negative charge, the force direction will be opposite to the direction indicated by the right-hand rule.
- In this case, if you point your thumb (V) towards the east (right), and your fingers (B) towards the north (up), your palm will face outwards, which indicates the force direction for a positive charge.

4. **Reverse the Direction for the Electron**:
- Since the electron has a negative charge, the force acting on it will be in the opposite direction to that indicated by your palm. Therefore, if the palm is facing outwards (up), the force on the electron will be directed downwards.

5. **Conclusion**:
- The force on the electron will be directed vertically downwards.

### Final Answer:
The force on the electron will be directed vertically downwards.