9Motion of a charged particle in the magnetic field
9Motion of a charged particle in the magnetic field.docx
1. A proton of kinetic energy 15
keV travelling at right angles to a magnetic field describes
a circle of radius of 5.0 cm. The mass of a proton is 1.7 ´ 10−27
a Show that the speed of the proton is 1.7 ´ 106
m s−1. 
b For this proton, calculate the centripetal force provided by the
magnetic field. 
c Determine the magnetic flux density of the magnetic field that
keeps the proton moving
in its circular orbit. 
d How long does it take for the proton to complete one orbit? 
2. The diagram shows a velocity-selector for charged ions. Ions of
speed v emerge from the slit.
The parallel plates have a
separation of 2.4 cm and are connected to a 5.0 kV supply.
A magnetic field is applied at right angles to the electric field between the
that the positively charged ions emerge from the slit of the velocity-selector
at a speed of 6.0 ´ 106 m s−1. Calculate the
magnetic flux density of the magnetic field.