HSC Questions

[sidzeman]

Hey could someone explain these 2 questions from the 2010 HSC please?

For the radial vs normal magnetic field question - could someone explain to me why Force remains constant in a parallel field? Should it not vary as per F =BILsin(theta)?

[Savas_P]

11. The outside ring will create increasing EMF, this changing flux in the inner loop be opposed by increasing current in the opposite direction (Lenz's law).

20. You have to use the right hand slap rule to see which motor on the right hand side is forced down, but I have no idea what the differences are in the pictures and how to tell which is north/south. someone pls explain

also the force is constant because the section of wire is perpendicular to the field, it only makes a difference with torque because the plane will be rotating and cutting different amounts of flux.