1. A reminder about current
Electron current
= drift speed of electrons
n = density of electrons (number per unit volume)
Conventional current i

2. Magnetic force on a current-carrying wire

3. Magnetic force on a current-carrying wire

4. Magnetic force on a current-carrying wire

5. Magnetic force on a current-carrying wire

6. Uniform magnetic field

7. Uniform magnetic field

8. Uniform magnetic field

9. Uniform magnetic field
True for curved wires too.

11. Torque on a current loop

12. Side view:
Net force is zero.

13. Net torque is not zero.

18. A magnetic dipole will align with the magnetic field.

19. N S N S

20. N S N S
This is why magnets point north...
as long as you are not too close to the poles.