Charges in Magnetic Fields – Practice


1) A electron enters a magnetic field with a strength of 0.5 T. The electron is travelling at 8 × 105 m/s at an angle of 24° to the magnetic field. Calculate the force experienced by the electron:

2) Determine the direction that the force acts on each of the particles below as they enter the magnetic field:

a) Positive charge moving into the page:

b) Negative charge moving to the left:

3) A positively charged particle with a mass of 2 × 10−25 kg, carrying a charge of 1.2 × 10−16 C travelling at 4.2 × 105 m/s enters a magnetic field of 0.005 T. What is the radius of its path?

4) Electrons are accelerated over a distance of 25cm by a potential difference of 25kV across a pair of parallel plates before entering a magnetic field with a strength of 0.15 T. (qe = -1.602 × 10−19 C and me = 9.109 × 10−31 kg)

a) Calculate the strength of the electric field:

b) Calculate the speed of the electrons as they exit the parallel plates:

c) Calculate the radius of the electron as a result of the magnetic field:

Quick Answers:

1) 2.6 × 10−14 N

2a) up    b) down

3)  14 cm

4a) 1 × 105 V/m    b) 9.4 × 107 m/s    c) 3.6 mm

Worked Answers: