Download Magnetic Fields Review

Magnetic Fields Review
1) What is the speed of an electron moving in a circular orbit of radius 8.0 nm in a magnetic field of strength
2.5 T? [3.5 x 103 m/s]
2) A magnetic field is aligned vertically down with a strength of 4.0 T. An alpha particle enters the field with a
velocity of 6.5 x 104 m/s [E]. Calculate the force on the alpha particle. [8.3 x 10-14 N [N]]
3) An electron is traveling at a velocity of 3.0 x 106 m/s [down] through a perpendicular magnetic field and
experiences a force of 1.00 x 10-12 N [N]. What is the magnetic field strength? [2.1 T [E]]
4) A copper wire of length 30.0 cm has electron flow of 2.0 A [N] through a magnetic field of 5.00 mT [up].
What is the force on the wire? [3.0 mN [W]]
5) A proton is accelerated from rest by 4000.0 V. The proton then enters a magnetic field at right angles with
a strength of 0.30 T. What is the magnitude of the force on the proton? [4.2 x 10-14 N]
6) A proton enters a magnetic field at right angles and ends up in a circular orbit. What is the momentum of
the proton if the radius of the orbit is 4.6 µm and the field strength is 2.6 kT. [1.9 x 10-15 kgm/s]
7) A charged particle enters a magnetic field at right angles and ends up in a circular path. If the magnetic
field strength was doubled, the speed of the particle was tripled and the charge on the particle was halved,
what would happen to the radius? [r2 = 3r1]
8) A charged object travels perpendicularly through a magnetic field of 2.0 T at 10.0 m/s. How many excess
electrons does the object have if it experiences a force of 3.2 nN? [1.0 x 109 electrons]
9) Compare the forces acting on an electron and a proton if they enter a magnetic field at right angles.
10) Calculate the magnitude of the magnetic force on a 140 m length of wire stretched between two towers
carrying a 200.0 A current. The Earth’s magnetic field is 5.0 x 10-5 T and it makes an angle of 60.0 degrees
with the wire. [1.2 N]
11) An electron is accelerated by a voltage of 5.0 kV. What radius will the electron have if it enters a 3.0 mT
magnetic field at right angles? [8.0 cm]
12a) What is the velocity of a beam of electrons that go undeflected when passing through perpendicular
electric and magnetic fields, if the fields have strengths of 3.8 kV/m and 2.5 mT? [1.5 x 106 m/s]
b) What radius will the electron’s path have when the electric field is switched off? [0.35 cm]
13) 2 wires have an attractive force between them when current flows in them. Compare the directions of
the current in the wires.
14) Draw a diagram showing the North pole of a bar magnet moving towards a coil, draw on the induced
current and poles in the coil.
15) Magnetic force between poles is an inverse square relationship: Fm = kS1S2/d2, where S is the magnetic
field strength and d is the distance between the poles. Calculate the factor by which the magnetic force
between poles would change if the strength of both magnets is tripled and the distance between the poles is
increased two times. [9/4]
16) Use domain theory to explain the following:
a) a magnet loses its magnetism when dropped.
b) a magnet broken in half becomes two magnets
c) an iron bar, when heated, becomes magnetized
17) A charge-to-mass ratio experiment has the following data:
a) Charged particles deflect in a magnetic field into a circular path with a radius of 109 mm when the
magnetic field had a strength of 1.23 mT.
b) An electric field, produced by parallel plates with 130 V and a plate separation of 12.0 mm, makes the
charged particle beam to travel straight (undeflected).
i) Find the speed of the charged particles. [8.8 x 106 m/s]
ii) Find the charge-to-mass ratio of the particles. [6.6 x 1010 C/kg]