Presentation on theme: "A charged particle accelerated to a velocity v enters the chamber of a mass spectrometer. The particle’s velocity is perpendicular to the direction of."— Presentation transcript:
A charged particle accelerated to a velocity v enters the chamber of a mass spectrometer. The particle’s velocity is perpendicular to the direction of the uniform magnetic field B in the chamber. After the particle enters the magnetic field, its path is a 1. parabola. 2. circle. 3. spiral. 4. straight line.
Example: Determine the direction of the force for each of the following situations. Into the page Left Up No Force Down
Electrons are emitted at the left of the device shown in the photograph at the left above. As they move from left to right in the partially evacuated tube, they pass through a defining slit and are rendered visible when the resulting beam strikes a fluorescent screen, as seen in the close-up photograph at the right. A bar magnet will now be moved close to the electron beam, with the North end of the magnet closest to the tube, so the magnetic field lines are pointed away from the viewer into the picture. What will happen to the path of the electron beam as the magnet is moved close to the tube? The electron beam will: (1) deflect upward. (2) deflect downward. (3) deflect into the picture. (4) deflect out of the picture. (5) remain moving along the same line.
A CuSO 4 solution is placed in a container housing coaxial cylindrical copper electrodes. Electric and magnetic fields are set up as shown. Uncharged pollen grains added to the solution are carried along by the mobile ions in the liquid. Viewed from above, the pollen between the electrodes circulates clockwise. The pollen is carried by ions that are 1. positive. 2. negative. 3. both positive and negative. 4. need more information E E B B
Example: A particle is positively charged to 10 C and moving at a velocity of 2000 m/s to the right through an external magnetic field with a strength of 5 x 10 4 T directed into the page. a)What is the magnetic force acting on the charge? b)What path would the charge follow if left in the magnetic field for a long time? c)What would the net force on the charge be if there was also an electric field of 2 x 10 7 V/m directed downward? a) Up = 90 o, sin90 o = 1 b)The charge will follow a circular path. c) down Up
We do not always only look at a single moving charge. Often we consider multiple charges, which is typically described as a current. The previous force equation can be modified to account for multiple charges. N is the number of charges present. Force on a current carrying wire Similarly, Microscopic view of current through a wire The quantity L is the length vector parallel to the wire that points in the direction of current flow. Current is not a vector!
Example: A square loop of wire with sides 20 cm long is placed in an external uniform magnetic field with a strength of 5 T directed out of the page. If a current of 5 A flows clockwise in the loop, what is the force on the right edge of the circuit? 1 Left The example above has the magnetic field perpendicular to the plane containing the circuit. What happens if the magnetic field is parallel to the plane containing the loop? Force on each side of the loop is directed towards the center of the circuit! Force on the top and bottom of the loop would be zero. 0 Force on the left and right sides of the loop would not be zero. 1 1 Into the page Out of the page Left: Right: