Please help me with working out

Which accurately compares concave and convex lenses?

What are two different ways you could find the value of a? explain these methods.

What would be the result of an alpha particle coming into a magnetic field? a) the alpha particle will stop moving. b) the alpha particle will reverse its direction. c) the alpha particle will be deflected in a curve path. d) the alpha particle will continue to travel in a straight line.