Here are the assigned problems. The problem solving handout gives specific instructions on how to solve these problems (as well as others you may encounter in other coruses or later in life).  The exercises will (until further notice) be handed out in class.

 

Charges Unit

Due Sep 3
You are spending the summer working for a chemical company. Your boss has asked you to determine where a chlorine ion of effective charge -e would situate itself near a carbon dioxide ion. The carbon dioxide ion is composed of 2 oxygen ions each with an effective charge -2e and a carbon ion with an effective charge +3e. These ions are arranged in a line with the carbon ion sandwiched midway between the two oxygen ions. The distance between each oxygen ion and the carbon ion is 3.0 x 10-11 m. Assuming that the chlorine ion is on a line that is perpendicular to the axis of the carbon dioxide ion and that the line goes through the carbon ion, what is the equilibrium distance for the chlorine ion relative to the carbon ion on this line? For simplicity, you assume that the carbon dioxide ion does not deform in the presence of the chlorine ion. ( Solution)

Due Sep 10
You've been hired to design the hardware for an ink-jet printer. You know that these printers use an electrode to deflect the droplets, causing them to form letters on a page. The basic mechanism is that uniform ink drops of about 2 x 10-6m radius are charged to varying amounts after being sprayed out towards the page at a speed of about 15 m/s. Along the way to the page, they pass into a region between two deflecting plates that are 1.5 cm long. The deflecting plates are 1.0 mm apart and produce a uniform electric field between them of 1.5 x 106 N/C. You measure the distance from the edge of the plates to the paper and find that it is one-half inch. Assuming an uncharged droplet forms the bottom of the letter, how much charge is needed on the droplet to form the top of a letter (standard 12 point font). ( Solution)

 

Electricity Unit

Due Sep 24
You have a great summer job in a university research laboratory. Unfortunately, during the summer there is an accident in the lab, and you are suddenly transported back in time. You find yourself face to face with J. J. Thomson in 1905. He is one of the scientists who is proposing a model of the atom where the positive charge is spread throughout the volume and the negative charges, electrons, are scattered in the positive charge. Affectionately, this is known as the “plum pudding model” as the electrons look like small raisins scattered in the dough. (As far as you can tell, plum pudding doesn’t actually contain any plums; silly British. You figure that the most similar food from your past would be your Aunt’s Christmas fruitcake.) From your physics and chemistry classes you know that Thomson’s model isn’t correct. In 1911 Rutherford and his coworkers will learn that the positive charge is confined to a small spot in the center- the nucleus. You want to convince Thomson that his model is flawed. You start discussing your ideas. He agrees with you that for hydrogen, the radius of the atom is 1.5 x 10-10m. He also understands that hydrogen can emit red light, which has an oscillation frequency of 6.0 x 1014Hz. You hope to show him that if his model were true, the electron inside hydrogen would have an oscillation frequency that differs from what is observed.
( Solution)


[A bit of background physics to help you. Whenever an object is subjected to a force which depends linearly on distance, the object will oscillate at a specific frequency. This is known as simple harmonic motion. Masses on the ends of springs do this. So do pendulums; as long as you stick with small oscillations. So, if the force is of the form F= -kx, where k is a constant that describes the spring (a big k is a stiff spring and a small k is a flimsy spring). The frequency of vibration will be , where m is the object’s mass. You can read more about these type of oscillations in chapter 13 of our text.]


Due Oct 1

For this week, our problem will actually consist of several exercises: 24-20P, 24-58P, 28-18P , 25-34P. Since these are our "problem" everybody is required to turn in solutions, no matter their grade option. Also note that since these are exercises, the full problem solving algorithm isn't feasible (there probably won't be many assumptions or approximations). However, you should still include the relevant parts such as an explanation of the relevant concepts, math with accompanying explanations, etc. ( Solution)


Due Oct 8
After you walk over carpet on a dry day, your hand comes close (within 1/2 cm) to a metal doorknob and a spark jumps across. How much charge did you accumulate in walking over the carpet? ( Solution)

 

Circuits Unit

Due Oct 22
1. You and your lab partner were having so much fun in lab this week, you decided to keep collecting data on the light bulb. On the next page, you see all of your glorious data. Now that you’ve got it, what can you do with it? After glancing at section 27.4 of our text, you realize that you can use the data to calculate the temperature of the tungsten filament when the bulb is fully lit.


2. You and a friend are studying for a midterm and the session goes until the early morning. At about 4 am you decide to cook some breakfast. Despite being sleepy, things are going well— the waffles are cooking and the coffee is perking. Should you make some toast now? The 1000watt waffle iron and the 600watt coffee maker are plugged into kitchen wall electrical outlets. You will also use a kitchen wall outlet for the toaster. The kitchen wall outlets are all part of the same 110V circuit which has a 20A circuit breaker (with negligible resistance) to protect the wire carrying the largest current from getting too hot. You know that if you plug in too many appliances you will overload the circuit breaker. The toaster label says that its power output is 700 watts. ( Solution)

 

Magnetism Unit
Due November 7
        You have landed a great summer job at UC-Irvine's medical school assisting in a research group investigating short lived radioactive isotopes which might be useful in fighting cancer.  Your group is working on a way of transporting alpha particles (helium nuclei) from where they are made to another room where they will collide with other material to form the isotopes.  Since the radioactive isotopes are not expected to live very long, it is important to know precisely how much time it will take to transport the alpha particles.  Your job is to design that part of the transport system which will deflect the beam of alpha particles (m = 6.64 x 10-27 kg, q = 3.2 x 10-19 C) through an angle of 90o by using a magnetic field.  The beam will be traveling horizontally in an evacuated tube.  At the place the tube is to make a 90o turn you decide to put a dipole magnet which provides a uniform vertical magnetic field of 0.030 T.  Your design has a tube of the appropriate shape between the poles of the magnet.  Before you submit your design for consideration, you must determine how long the alpha particles will spend in the uniform magnetic field in order to make the 90o-turn. ( Solution)


Due November 14
           Since the MTA union workers went on strike there have been more cars on the road, which is motivating you to think about the next generation of transportation. The idea that you have is for a new commuter train that is based on a rail gun. Two parallel metal rails, each of width 10cm, are separated by a gap of 1 meter. At the distant ends, the two rails are connected to the two terminals of a power supply. One set of the train’s wheels and axle are made of a conductor thereby completing the circuit, allowing current to flow through the power supply, rails and axle. From present trains you know that the axles on the train are responsible for a frictional force of about 20,000 N. Will your design be feasible? Is the current required to produce constant speed motion realistic for a commuter train?
( Solution)

"Electromagnetism Unit"
Due November 24
An essay related to an article from the New Yorker ("Calamity on Meadow Street" by Paul Brodeur, July 9, 1990). A copy of the article is on reserve in the library as well as on ERes. (Our ERes password is the same as this web site.)

After you've read the article, you should write a letter to the editor in response to Brodeur's article. (This means that you should imagine that your audience is comprised of well-educated people, but who probably have a limited physics background.) Specifically, comment on the how scientific the author's theories are. You may wish to propose additional theories of your own. You should also describe scientific experiments you could perform (with enough equipment) to support your theories or the author's. Your letter should be concise (approximately 2-3 pages, double spaced) and well-worded. Your letters will be graded on their scientific merit, logic and level of detail, in addition to grammar and coherence. (Anybody who quotes the dictionary will recieve a zero on this problem.)