In fig. 30.11, suppose that and with switch open, switch is left closed until a constant current is established. then is closed and opened, taking the battery out of the circuit. (a what is the initial current in the resistor, just after is closed and is opened? (b what is the current in the resistor at (c what is the potential difference between points b and c at which point is at a higher potential? (d how long does it take the current to decrease to half its initial value?

In a particle accelerator a positron (C= +1.6 x 10-19) travels through a perpendicular magnet field with a magnitude of 3.1 x 10-2 T. At what speed must the positron travel in order for it to experience a force of 4.75 x 10-14 N? 28. An alpha particle (2 protons and 2 neutrons) experiences a downward force of 2.9 x 10-14 N while traveling in a magnetic field with a strength of 5.1 x 10-19 T pointing to the north. Find the speed of the particle and the direction it must be traveling in. 29. Find the length of a wire if it experiences a .63N force when it travels through a magnetic field with a strength of 0.85T whilst carrying 5.0 amps of current. 30. A coil with 462 turns of wire, a total resistance of 36Ω , and a cross-sectional area of 0.25 m2 is positioned with its plane perpendicular to the field of a powerful electromagnet. What average current is induced in the coil during the 0.37s that the magnetic field drops from 3.1 T to 0.0 T? 31. A step-up transformer has a potential difference across the primary of 28 V and a potential difference across the secondary of 3.0 × 104 V. There are 28 turns in the primary coil. How many turns are in the secondary? 32. A step-up transformer is used to create a potential difference of 1.6872 × 105 V across the secondary. The potentia