(5-6) The figure at right depicts a square wire coil in a region of constant mag
ID: 1461460 • Letter: #
Question
(5-6) The figure at right depicts a square wire coil in a region of constant magnetic field pointing in the +y direction. A current flows in the coil in the direction shown (the arrowhead indicates the current direction on the side of the square nearest you.) The square coil makes an angle of a with the xz-plane. 5. The magnetic field will tend to make the loop rotate a Clockwise (decreasing a) b. Counterclockwise (increasing a) 6. At which angle a does the coil have the lowest potential energy? a. alpha = 0 b. alpha = 45 c. alpha = 90 (7-9) An electron of mass m and charge q is accelerated to the right (in the plane of the page) from rest through a potential difference V. The electron then enters a region, defined by x > 0, containing a uniform magnetic field. 7. When the electron enters the region with the magnetic field the force on it is directed a. toward the top of the page b. toward the bottom of the page c. into the page 8. When the electron is in the magnetic field region, its speed v a. increases. b. decreases. c. remains constant.Explanation / Answer
(7-9)
(7)the magnetic force on the elcectron is given by F = - q (V XB)
V= velocity of electron
Here direction of B is out of the plane of page
the direction of force can be found by cross product rule or right hand rule.we move the curl of fingers from V to B , the direction in which thumb points is the direction of force.in this case the force of elcectron is towards the top of the page.so option a is correct
(8) the magentic force on the electron provides the centripetal force and tries to move the electron in a circular path.the equation is gven by
MV^2/R = qV B sin (90)
now the mgnetic force F and the velocity V are perpendicular to each other. so the work done by magnetic force on the electron is zero. when W=0, the kinetic energy of the electron does not change according to work energy principle. so the speed of electron remains constant.so option c is the correct one.
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