Physics 202 MWF 10:20 Spring 2002 (Ford)
Final Exam
Show all your work. Partial credit will be given if earned. Write your
answers in the blanks provided.
(8 pts) 1. Two long straight wires carry currents as shown. The wires are parallel and are 0.04 m apart. What are the magnitude and direction of the resultant magnetic field at point P, midway between the two wires?
Ans. magnitude __________________
direction ______________
(10 pts) 2. Charge q1 = +3 × 10-6 C is on the x-axis at x = 0.4 m and charge q2 = -3 × 10-6 C is on the x-axis at x = -0.4 m. Point P is on the y-axis at y = +0.3 m. Calculate the magnitude and direction of the resultant electric field produced at point P by these two charges.
Ans. magnitude ________________
direction _________________
(8 pts) 3. Three resistors are connected to a battery as shown in the sketch.
R1 = 3 
, R2 = 4 , and R3 = 6 . The current through R1 is 2 A.
a) What is the voltage V of the battery?
Ans. ___________
b) What is the current through R3?
Ans. ________________
(10 pts) 4. A small object with charge q1 = +5 × 10-6 C is held fixed and doesn't move. Another small object with charge q2 = -2 × 10-6 C and
mass 4.0 × 10-3 kg is moving toward q1 and has a speed of 30 m/s when it is 0.060 m from q1. What is the speed of q2 when it is 0.020 m from q1?
Ans. __________________
(8 pts) 5. The triangular loop of wire shown in the sketch carries a current of I= 2 A in the direction shown. Find the force exerted by the magnetic field on each side of the triangle. If the force is not zero, specify its direction. The magnetic field is uniform, has magnitude B = 4 T, and is in the direction shown.
a) side PQ
Ans. magnitude ______________
direction ______________
b) side QR
Ans. magnitude _______________
direction ____________
c) side PR
Ans. magnitude ________________
direction ______________
(9 pts) 6.
a) The current I in the long straight wire is decreasing. Show on the sketch the direction of the induced current through R.
b) The emf 
in circuit A is increasing. Show on the sketch the direction of the induced current through R.
c) The bar in the sketch is being pulled to the right on conducting rails. The magnetic field is directed into the page. Show on the sketch the direction of the induced current in the resistor R.
(8 pts) 7. An ac circuit consists of a resistor with
R = 600 and an inductor with inductance 0.3 H in series with an ac source. The rms voltage across the resistor is 30 V and the rms voltage across the source is 50 V.
a) What is the rms voltage across the inductor?
Ans. ____________
b) What is the frequency f of the source?
Ans. _____________
c) Does the source voltage lag or lead the current in the circuit?
Ans. _____________
(8 pts) 8. A diverging lens with focal length -30 cm forms a virtual image of an object. The image is 15 cm from the lens.
a) Is the image upright or inverted?
Ans. ___________
b) How far is the object from the lens?
Ans. _______________
(8 pts) 9. A thin sheet of plastic with refractive index 1.2 is on top of a flat piece of glass that has index of refraction 1.5. Coherent light of wavelength 500 nm in air is incident perpendicular to the surface of the plastic. What is the minimum nonzero thickness of the plastic for which there will be destructive interference between the light reflected at the top and bottom surfaces of the plastic sheet?
Ans. _______________
(9 pts) 10. Electrons with speed v are incident on two very narrow slits that are separated by 0.05 mm. The resulting interference pattern is observed on a screen that is 4 m from the slits. On the screen the distance between the centers of adjacent interference maxima is 0.08 mm. What is the speed v of the electrons?
Ans. _______________
(8 pts) 11. 13153I has a half-life of 8.0 days.
a) What is the mass of a sample of 13153I that has an activity of one curie
(3.7 × 1010 counts/s)?
Ans. ___________
b) A sample of 13153I has an initial activity of 8.0 × 1010 counts/s. After how many days will the activity be 2.0 × 1010 counts/s?
Ans. ____________
(6pts) 12. How many neutrons and how many protons are there in the daughter nucleus produced by the following decays?
a) 
decay of 21084Po
Ans. neutrons ______________
protons ___________
b) 
+ (positron) decay of 116C
Ans. neutrons ______________
protons ___________
c) - decay of 21182Pb
Ans. neutrons _____________
protons ______________