Physics 202 MWF 10:20 Spring 1998 (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 point charges are placed on the x-axis as shown in the sketch. Charge q₁ = -6.0 × 10^-6 C is at x = -1.0 m and charge q₂ = +2.00 × 10^-6 C is at the origin (x = 0). Point A is on the x-axis at x = +2.0 m. Calculate the magnitude and direction of the resultant electric field at point A produced by these two point charges.

Ans. E = ___1500 N/C____

direction ___to left (-x)_____________


(10 pts) 2. Consider the circuit shown in the sketch. Initially there are no currents anywhere in the circuit.

a) The switch S is closed at time t = 0. Just after the switch is closed, what are the voltages v_ab and v_cd across the two resistors?

Ans. v_ab ___90 V____

v_cd ___0___

b) After the switch has been closed a long time, what are the voltages v_ab and v_cd across the two resistors?

Ans. v_ab ___90 V___

v_cd ___90 V___

c) After the switch has been closed a long time it is opened again. Just after the switch is opened again, what are the voltages v_ab and v_cd across the two resistors?

Ans. v_ab ___-45 V___

v_cd __+90 V___


(10 pts) 3. 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 = 2.0 × 10^-5 F.

a) What is the current amplitude in the circuit

Ans. ___0.176 A___

b) Does the source voltage lag or lead the current?

Ans. ___lags___

c) Voltmeters V₁, V₂, V₃₁, V₄, and V₅, calibrated to read the rms voltage, are connected as shown below. The voltmeters each have infinite resistance so no current flows through them. What is the reading of each voltmeter?

Ans. V₁ = ___49.9 V__

V₂ = ___125 V___

V₃ = ___56.2 V___

V₄ = ___68.8 V___

V₅ = ___84.9 V___

(12 pts) 4. Consider the circuit shown in the sketch.

a) When the switch S is open and all currents and charges have reached their final values, what are the charges Q₁ and Q₂ on each capacitor?

Ans. Q₁ = __66.7 µC___

Q₂ = ___66.7 µC___

b) The switch S is closed. After it has been closed a long time, what are the charges Q₁ and Q₂ on each capacitor?

Ans. Q₁ = ___140 µC___________

Q₂ = ___30 µC____


(10 pts) 5. An object 2.0 mm tall is placed 40 cm to the left of a diverging lens that has focal length f₁ = -10 cm. A second converging lens, with focal length f₂ = +10 cm is 17 cm to the right of the first lens.

a) How far is the final image from the object?

Ans. ___73.7 cm___

b) Is the final image real or virtual?

Ans. ___real___

c) Is the final image erect or inverted?

Ans. ___inverted__

d) What is the height of the final image?

Ans. ___0.267 mm__


(8 pts) 6. The maximum wavelength of light that will eject photoelectrons from a given surface is 320 nm.

a) What is the work function for this surface? You must express your answer in eV.

Ans. ___3.87 eV__

b) Calculate the maximum kinetic energy of the electrons ejected from this surface by light of wavelength 150 nm. You must express your answer in eV.

Ans. ___4.39 eV___


(8 pts) 7. A thin sheet of plastic with refractive index 2.0 is on top of a flat sheet of glass that has index of refraction 1.5. Coherent light of wavelength = 600 nm in air is incident perpendicular to the surface of the plastic.

a) What is the speed of the light in the plastic sheet?

Ans. ___1.50 × 10⁸ m/s___

b) What is the minimum thickness of the plastic for which there will be constructive interference between the light reflected at the top and bottom surfaces of the plastic film?

Ans. ___75 nm___


(9 pts) 8. There is a uniform magnetic field B in a cylindrical region of radius a = 0.50 m. B is directed into the plane of the paper, has an initial value of 2.0 T, and is increasing in magnitude at a uniform rate of +0.05 T/s. A conducting metal ring with resistance 5.0 and radius r = 0.90 m encircles the field region, with the center of the ring at the center of the field region.

a) While the magnetic field is increasing in magnitude, what is the magnitude of the current induced in the metal ring?

Ans. ___0.00785 A____

b) Is the induced current in the ring in the counterclockwise or clockwise direction?

Ans. ___counterclockwise___


(10 pts) 9. A point charge q₁ = +5.0 × 10^-6 C is held fixed at the origin. A second point charge with mass m = 0.060 kg and charge q₂ = +7.0 × 10^-6 C is released from rest at a distance of 0.30 m from the first charge. What is the speed of q₂ when it reaches point P, a distance of 0.50 m from q₁?

Ans. ___3.74 m/s___


(9 pts) 10. A particle with charge q = -3 × 10^-6 C is moving in the direction shown with speed v = 5 × 10⁵ m/s in a region where there are perpendicular electric and magnetic fields. The magnetic field has magnitude 0.7 T and is directed into the plane of the paper.

a) What are the magnitude and direction of the force that the magnetic field exerts on the particle?

Ans. magnitude ___1.05 N____

direction __to the right___

b) What must be the magnitude and direction of the electric field in the region if the particle is to move in a straight line with constant speed through the region? (Neglect gravity.)

Ans. magnitude ___3.5 × 10⁵ N/C___

direction ___to the right___


(6 pts) 11. Calculate the binding energy (in MeV) of the boron isotope ¹¹₅B. The atomic mass of ¹¹₅B is 11.009305 u.

Ans. ___76.2 MeV___