Physics 202 MWF 10:20 Spring 1995 (Ford)
Final Exam
Show all your work. Partial credit will be given if earned. Write your answers in the blanks provided.


(9 pts) 1. An object is 9.0 m from the wall. You want to use a concave mirror to project an image of the object onto the wall, with the height of the image four times the height of the object.

a) Is the image real or virtual?

Ans. ______________

b) Is the image erect or inverted?

Ans. _____________

c) How far should the mirror vertex be from the object?

Ans. _____________


(10 pts) 2. A positive point charge q₁ = +6.0 × 10^-9 C is placed at the origin and a negative point charge q₂= -4.0 × 10^-9 C is placed on the y-axis at y = +3.0 m. Point P is on the x-axis at x = +4.0 m.

a) On the sketch below clearly show the directions of the electric fields E₁ and E₂ at point P due to each of the two point charges.

b) Calculate the magnitude of the resultant field at point P produced by these two point charges.

Ans. ________________


(11 pts) 3. A potential difference of 300 V is established between two very large parallel metal plates that are 2.0 cm apart by placing charge +Q on one plate and charge -Q on the other plate.

a) An electron (mass 9.11 × 10^-31 kg and charge -1.6 × 10^-19 C is released from rest just above the negative plate A. What is the speed of the electron just before it reaches the positive plate B? Neglect the effects of gravity.

Ans. _____________

b) What are the magnitude and direction of the electric field produced by the two plates at a point midway between them? (Give the direction as either from A to B or from B to A.)

Ans. E = _________________

direction _________________


(10 pts) 4. A circular loop of wire with resistance R = 0.4 is in a region of uniform magnetic field. The magnetic field is directed out of the page of the paper and is decreasing at a uniform rate B/t = -0.03 T/s. The current induced in the wire loop is 0.2 A.

a) Is the induced current clockwise or counterclockwise?

Ans. _________________

b) What is the radius r of the wire loop?

Ans. _________________


(10 pts) 5. Two long, straight, parallel wires separated by 0.20 m carry currents in the same direction as shown in the sketch.

a) What are the magnitude and direction of the resultant magnetic field produced by two wires at a point midway between them?

Ans. B = _______________

direction ______________

b) A small particle with charge q = -5.0 × 10^-4 C is moving between the wires. When the particle is in the plane of the wires and midway between them, the force F that the magnetic field of the wires exerts on it has magnitude 3.0 × 10^-5 N and is directed to the right. At this instant, what are the magnitude and direction of the velocity of the particle? (Show the direction of the velocity on the sketch.)

Ans. _____________


(12 pts) 6. The circuit shown in the sketch has an emf, two resistors, an inductor, and a switch. At t = 0 the switch is closed.

a) Just after the switch is closed, what is

i) the current i₁ through R₁?

Ans. ____________

ii) the potential difference V_a - V_b?

Ans. ____________

b) After the switch has been closed a long time, what is

i) the current i₁ through R₁?

Ans. ___________

ii) the potential difference V_a - V_b?

Ans. ___________

(8 pts) 7. In the circuit shown below the currents and capacitor charges have reached their final constant values. What are the charges Q₁ and Q₂ on each capacitor?

Ans. Q₁ = ______________

Q₂ ______________


(7 pts) 8.
a) Calculate the binding energy (in MeV) of the lithium isotope ⁶₃Li. The mass of ⁶₃Li is 6.015121 u.

Ans. ____________

b) The nucleus ²¹⁰₈₂Pb undergoes ^- decay. What are the nucleon number A and atomic number Z of the nucleus that is produced by this decay?

Ans. A = ______________

Z = _______________


(10 pts) 9. A thin sheet of plastic with refractive index 2.5 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. __________________

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. ______________


(6 pts) 10. When light of wavelength 400 nm is incident on a metal surface, the maximum kinetic energy of the photoelectrons that are produced is 1.8 eV.

a) What is the maximum kinetic energy of the photoelectrons that are produced when light of wavelength 300 nm is incident on the same surface?

Ans. ____________

b) What is the longest wavelength of light that will cause photoelectrons to be emitted from this surface?

Ans. ________________


(7 pts) 11.
a) An atom is in an initial state that has energy 6.0 eV. The atom emits a photon of wavelength 800 nm. What is the energy ( in eV) of the final state of the atom?

Ans. ____________

b) If two photons of the same energy are produced in p⁺p^- annihilation, find the wavelength of each photon.

Ans. ____________