Question 1. Question 2. Question 3

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Christian Marshall
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1 Question 1 Switch S in in the figure is closed at time t = 0, to begin charging an initially uncharged capacitor of capacitance C = 18.2 μf through a resistor of resistance R = 22.3 Ω. At what time (in ms) is the potential across the capacitor equal to that across the resistor? Question 2 The figure shows the circuit of a flashing lamp, like those attached to barrels at highway construction sites. The fluorescent lamp L (of negligible capacitance) is connected in parallel across the capacitor C of an RC circuit. There is a current through the lamp only when the potential difference across it reaches the breakdown voltage V L ; then the capacitor discharges completely through the lamp and the lamp flashes briefly. For a lamp with breakdown voltage V L = 71.4 V, wired to a 92.7 V ideal battery and a mf capacitor, what resistance R is needed for 3 flashes per second? Question 3 Figure shows three situations in which a positively charged particle moves at velocity through a uniform magnetic field and experiences a magnetic force. In each situation, determine whether the orientations of the vectors are physically reasonable.

(a) (b) (c) Question 4 Figure 28-27 shows the path of an electron that passes through two regions containing

2 (a) (b) (c) Question 4 Figure shows the path of an electron that passes through two regions containing uniform magnetic fields of magnitudes B 1 and B 2. Its path in each region is a half-circle. Which field is stronger?

3 What is the direction of each field? : : Is the time spent by the electron in the region greater than, less than, or the same as the time spent in the region? Equal to Greater than Less than Question 5 A proton traveling at 21.2 with respect to the direction of a magnetic field of strength 3.57 mt experiences a magnetic force of 9.28 x N. Calculate (a) the proton's speed and (b) its kinetic energy (in ev). (a)

4 (b) - the number of significant digits is set to 3; the tolerance is +/-5% Question 6 An electron moves through a uniform magnetic field given by = B x +(3.77 B x ). At a particular instant, the electron has velocity = ( ) m/s and the magnetic force acting on it is ( ) N. Find B x. Question 7 An alpha particle (q = +2e, m = 4.00 u) travels in a circular path of radius 5.14 cm in a uniform magnetic field with B = 1.38 T. Calculate (a) its speed, (b) its period of revolution, (c) its kinetic energy (in ev), and (d) the potential difference (in V) through which it would have to be accelerated to achieve this energy. (a) (b) (c) (d) *3 *4 - the number of significant digits is set to 3; the tolerance is +/-5% *3 - the number of significant digits is set to 3; the tolerance is +/-5% *4 - the number of significant digits is set to 3; the tolerance is +/-5%

5 Question 8 A certain commercial mass spectrometer (Fig ) is used to separate uranium ions of mass 3.92 x kg and charge 3.20 x C from related species. The ions are accelerated through a potential difference of 92.4 kv and then pass into a uniform magnetic field, where they are bent in a path of radius m. After traveling through 180 and passing through a slit of width 1.46 mm and height cm, they are collected in a cup. (a) What is the magnitude of the (perpendicular) magnetic field in the separator? If the machine is used to separate out 1.36 mg of material per hour, calculate (b) the current (in A) of the desired ions in the machine and (c) the thermal energy (in J) produced in the cup in 1.18 h. (a) (b) (c) *3 - the number of significant digits is set to 3; the tolerance is +/-5% *3 - the number of significant digits is set to 3; the tolerance is +/-5%

Physics 212 Midterm 2 Form A

Physics 212 Midterm 2 Form A 1. A wire contains a steady current of 2 A. The charge that passes a cross section in 2 s is: A. 3.2 10-19 C B. 6.4 10-19 C C. 1 C D. 2 C E. 4 C 2. In a Physics 212 lab, Jane measures the current versus