Physics 202 MWF 10:20 Spring 1999 (Ford)
Final Exam
Show all your work. Partial credit will be given if earned. Write your
answers in the blanks provided.
(9 pts) 1. Two long, straight, parallel wires carry current I = 2 A in opposite directions as shown in the sketch. The wires are separated by 0.20 m. Point P is 0.10 m above wire 1. What are the magnitude and direction of the net magnetic field at point P produced by the currents in the two wires?
Ans. B = _______________
direction _____________
(10 pts) 2. Three capacitors are connected to a voltage source as shown in the sketch. C1 = 3.0 × 10-6 F, C2 = 5.0 × 10-6 F, and
C3 = 4.0 × 10-6 F. The voltage across C1 is V1 = 70 V.
a) What is the voltage V2 across C2?
Ans. ________________
b) What is the voltage V of the source?
Ans. ________________
c) What is the charge q3 on C3?
Ans. _______________
(10 pts) 3. Three resistors are connected as shown in the sketch to a voltage source with voltage V. The resistances are R1 = 15 
,
R2 = 25 , and R3 = 40 . The current through R1 is I1 = 3 A.
a) What is the current I2 through R2?
Ans. _______________
b) What is the current I3 through R3?
Ans. ________________
c) What is the voltage V of the source?
Ans. ______________
(12 pts) 4. A point charge q1 = -8.0 × 10-6 C is held fixed on the x-axis at x = +0.40 m and a point charge q2 = +3.0 × 10-6 C is held fixed on the x-axis at x = -0.40 m.
a) Find the magintude and direction of the net electric field at the origin that is produced by these two point charges.
Ans. E = ______________
direction ______________
b) A point charge q3 = -2.0 × 10-6 C is moved in along the y-axis, starting at a great distance and ending up at the origin. Calculate the net work done on q3 by the electric force of q1 and q2. Be sure to say whether the work done by the electric force is postive or negative.
Ans. _________________
(10 pts) 5. A particle with negative charge q = -3.0 × 10-6 C and speed v = 5.0 × 104 m/s enters a region of uniform electric and magnetic fields as shown in the sketch. The magnetic field has magnitude B = 0.70 T and is directed out of the plane of the paper.
What are the magnitude and direction of the electric field if the particle is to pass through the region undeflected and with constant speed?
Ans. E = ______________
direction ______________
(8 pts) 6. A future space station in orbit about the earth is being powered by an electromagnetic beam from the earth. The beam has a cross-sectional area of 120 m2 and transmits an average power of 8.0 × 103 W.
a) What is the rms value of the magnetic field in the beam?
Ans. _______________
b) How much energy is contained in a 5.0 m length of the beam?
Ans. _______________
(11 pts) 7. An object 2.0 mm tall is placed 15 cm to the left of a diverging
lens which is in turn 14 cm to the left of a converging lens. The diverging
lens has f1 = -10 cm and the converging lens has f2 = +10 cm.
a) How far is the final image from the object?
Ans. ______________
b) Is the final image real or virtual?
Ans. ________________
c) Is the final image upright or inverted?
Ans. _________________
d) What is the height of the final image?
Ans. _________________
(10 pts) 8. A plastic film with index of refraction 2.5 is put on the surface of the glass in a picture frame to decrease the reflectivity. The glass has index of refraction 1.6. What minimum thickness (not counting zero thickness)
of the plastic film is required if light of wavelength (measured in air)
400 nm reflected from the two sides of the film is to interfere destructively?
Ans. ___________________
(6 pts) 9.
a) An atom emits a photon when it undergoes a transition from a level with energy -1.20 eV to a level with energy -1.50 eV. What is the wavelength of the photon that is emitted?
Ans. __________________
b) What is the kinetic energy of an electron (mass 9.11 × 10-31 kg) that has De Broglie wavelength 800 nm?
Ans. _________________
(7 pts) 10. What is the total kinetic energy in MeV of the decay products when 146C undergoes 
- decay? (Note:
the atomic mass of 146C is 14.003241 u and the atomic mass of 147N is 14.003074 u.)
Ans. __________________
(7 pts) 11. The half-life of 146C is 5730 years. The activity per gram for the 146C in
the remains of an animal found frozen in a glacier is found to be 35% of the activity per gram when the animal was alive. How many years ago did the animal die?
Ans. _______________