Physics 202 MWF 10:20 Spring 2003 (Ford)
Final Exam
Show all your work. Partial credit will be given if earned. Write your
answers in the blanks provided.
(10 pts) 1. Point charge q1 = -5.0 × 10-9 C is on the x-axis at x = -0.20 m and point charge q2 is on the x-axis at
x = +0.40 m. The resultant electric field at the origin due to these two charges is 2100 N/C, in the +x-direction. What is q2 (sign and magnitude)?
Ans. magnitude __________________
sign _______________
(10 pts) 2. A small, charged metal sphere that carries a net charge of q1 = +5.0 × 10-6 C is held stationary by an insulating support. A second small metal sphere,with a net charge of +3.0 × 10-6 C is projected toward q1. When the two spheres are 0.800 m apart, q2 is moving toward q1 and has kinetic energy 0.80 J. How close does q2 get to q1? Assume that the two spheres can be treated as point charges and neglect the effects of gravity.
Ans. ___________________
(10 pts) 3. A conducting rod of length 1.5 m moves to the right at constant speed along conducting rails. There is a uniform magnetic field of B = 3.0 T that is directed into the plane of the figure. An electric heater with resistance 8.0 
, is connected between the rails, the induced current passes through the heater, and the heater consumes 24 W of power. The resistance of the rails and of the rod can be neglected.
a) How fast is the bar moving?
Ans. __________________
b) Is the current in the circuit clockwise or counterclockwise?
Ans. __________________
c) What is the magnitude of the external force that must be applied to the bar to keep it moving to the right at the constant speed found in part (a)?
Ans. ___________________
(12 pts) 4.
a) In the circuit sketched below the current through the 6 resistor is 4.0 A, as shown. What is the current I1 through the 25 resistor and the current I2 through the 20 resistor?
Ans. I1 __________________
I2 __________________
b) Two capacitors are connected in series as shown in the sketch. The capacitors have capacitances C1 = 3.0 × 10-6 F and C2 = 6.0 × 10-6 F. After the charges have reached their final values, the voltage across capacitor C1 is 20 V. What is the emf of the battery?
Ans. _______________
(10 pts) 5. A long, straight wire carries a current of 6.0 A in the
direction shown. An electron (charge q = -1.60 × 10-19 C and mass
m = 9.11 × 10-31 kg) is moving near the wire with a speed of
v = 4.0 × 105 m/s.
a) At the location of the electron, 0.020 m above the wire, what are the
magnitude and direction (up,
down, right, left, into paper, out of paper) of the magnetic field
produced by the current in the wire?
Ans. B = ________________
direction _______________
b) At the instant that the electron is moving
away from the wire, what are the magnitude and direction (up,
down, right, left, into paper, out of paper) of the force exerted
on the electron by the magnetic field of the wire?
Ans. F = __________________
direction _____________________
(10 pts) 6. An ac series circuit consists of a source with voltage amplitude V = 120 V and angular frequency 50 rad/s, a resistor with
resistance R = 400 , an inductor with inductance L = 9.0 H, and a
capacitor with capacitance C.
a) For what value of C will the current amplitude I be a maximum?
Ans. ________________
b) When C has the value calculated in part (a), what is the voltage amplitude across the inductor?
Ans.__________________
(10 pts) 7. A 5.00 mm tall object is to the left of a converging lens with a focal length of 6.0 cm. The image is
40.0 mm tall and erect.
a) How far is the object from the lens?
Ans. ____________________
b) How far is the image from the lens?
Ans. __________________
c) Is the image real or virtual?
Ans. __________________
(8 pts) 8. Two radio antennas A and B radiate in phase. Antenna B is
110 m to the right of antenna A. Consider point Q along the extension
of the line connecting the antennas, a distance of 55 m to the right of
antenna B. The antennas radiate waves of the same frequency, and this
frequency can be varied. What is the smallest frequency for which there will
be destructive interference at point Q?
Ans.__________________
(10 pts) 9.
a) An electron has de Broglie wavelength 200 nm. What is the energy of the electron, in eV?
Ans. _________________
b) A photon has momentum 6.63 × 10-24 kg·m/s. What is the energy of the photon?
Ans. ____________________
(10 pts) 10.
a) A one gram sample of radium 22688Ra has an activity of 3.7 × 1010 decays/s. Use this to calculate the half-life of this isotope of radium.
Ans. ________________
b) The 22688Ra isotope undergoes alpha decay. How many neutrons and how many protons are in the daughter nucleus produced by this decay?
Ans. neutrons _______________
protons________________
c) The 22888Ra isotope undergoes beta-minus decay. How many neutrons and how many protons are in the daughter nucleus produced by this decay?
Ans. neutrons ___________________
protons ______________