Using Fleming's left hand rule: point your centre finger towards west and thumb towards north. If we look at our fore finger, it will be pointing upwards. Thus, the magnetic field is in the upward direction.

Introduction:
When a positively charged alpha particle is projected towards the west and is deflected towards the north by a magnetic field, we can determine the direction of the magnetic field using the right-hand rule.

Right-Hand Rule:
The right-hand rule is a technique used to determine the direction of the magnetic field or the force acting on a charged particle in a magnetic field. It states that if you point your right thumb in the direction of the velocity of the charged particle and your fingers in the direction of the magnetic field, then the direction in which your palm faces will represent the direction of the force experienced by the particle.

Explanation:
1. The alpha particle is projected towards the west, which means its velocity is towards the west.
2. When the alpha particle enters the magnetic field, it experiences a force due to the interaction between its velocity and the magnetic field.
3. According to the right-hand rule, we can determine the direction of the force acting on the alpha particle by pointing our right thumb towards the west (velocity direction) and our fingers towards the north (deflection direction).
4. If we do so, our palm will face upwards, indicating that the force is acting upwards on the alpha particle.
5. The force acting on a positively charged particle (like the alpha particle) due to a magnetic field is perpendicular to both the velocity of the particle and the magnetic field direction.
6. Since the force is acting upwards on the alpha particle, we can conclude that the magnetic field must be directed towards the south.
7. This is because the magnetic field direction is opposite to the direction of the force experienced by the positively charged particle.

Conclusion:
In conclusion, if a positively charged alpha particle is projected towards the west and is deflected towards the north by a magnetic field, the direction of the magnetic field will be towards the south. This can be determined using the right-hand rule, which states that the direction of the force acting on a charged particle in a magnetic field can be determined by pointing the right thumb in the direction of the particle's velocity and the fingers in the direction of the magnetic field.