Question

a proton (positive charge) is traveling due south enters a region that contains a uniform magnetic field that points due west. in which direction will the proton be deflected?

a)down

b)up

c)east

d)west

e)north

I know that the answer is down but please explain.

Answer 1

every charged particle in a magnetic field experiences magnetic force F = q*v*B

the direction of force is perpendicular to the plane containing v and B

Now using Fleming's right hand rule

which states that strectch right hand such that Fore finger , middle finger and thumb are mutually perpendicular to each other ,then Fore finger in the direction of magnetic field and middle finger in the direction of particle ,then thumb gives the direction of the force

So according to this fore finger along west ,middle finger is along the north and finally thumb will be down wards

so the answer is a) down