A positively-charged particle (alpha particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is:

Options

A. (a) towards south
B. (b) towards east
C. (c) downward
D. (d) upward.

Explanation

To determine the direction of the magnetic field when a positively charged particle (like an alpha particle) is projected towards the west and deflected towards the north, we can use the right-hand rule. Here’s a step-by-step solution:

### Step-by-Step Solution:

1. **Identify the Direction of Motion of the Particle:**
- The alpha particle is projected towards the west. This means its velocity vector is directed towards the west.

2. **Identify the Direction of Deflection:**
- The particle is deflected towards the north. This means the magnetic force acting on the particle is directed towards the north.

3. **Use the Right-Hand Rule:**
- To apply the right-hand rule, extend your right hand.
- Point your fingers in the direction of the velocity of the positively charged particle (west).
- Curl your fingers towards the direction of the magnetic force (north).

4. **Determine the Direction of the Magnetic Field:**
- Your thumb will now point in the direction of the magnetic field.
- In this case, when you point your fingers west and curl them towards the north, your thumb will point upwards (out of the plane).

5. **Conclusion:**
- Therefore, the direction of the magnetic field is upwards.

### Final Answer:
The direction of the magnetic field is **upwards**.

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