Physics 122 Assignment 5B Prof. E. F. RedishThere will be a full period mid-semester exam next Thursday, March 6. If will cover the material covered inlecture through Thursday, February 28th and the readings inCLRC 3, Chapters 22-23 and 25--30 orC&J Chapters 18-21.All problems this week are practice exam problems. Most of them actually appeared on previous exams in thisclass.Do the following problems:1.(From an exam) In this problem, we will consider situations corresponding to three different long thin lines ofmatter containing charges:. a a copper wire carrying an electric current,. b a long amber rod that has been rubbed with fur and has a uniform excess of negative charge, and. c a beam of electrons passing through a vacuum inside a cathode ray tube. They are represented schematicallyin the figure below. The direction of the electric current and of the electron flow are from left to right. Alocation marked x is indicated on the diagram and a set of directions with labels are shown at the right.For each of the three cases, indicate in what direction the electric and magnetic fields at the location xwould point. If any of the fields are zero, write 0.CaseDirection of Electric Field atxDirection of Magnetic Field atxcurrent carryingwire rubbed amber rodelectron beam Now consider placing a positive charge at the location x. In one case it is stationary, while in a second caseit is moving in the direction C. Indicate the direction you believe nearest to the total force the charge wouldfeel. (Ignore gravity and air resistance.)CaseDirection of force on stationary + chargeat xDirection of force on + charge moving in C directionat xcurrent carryingwire rubbed amber rod electron beam 2. (From an exam) Flourescent bulbs deliver the same amount of light using much less power. If one kW-hrcosts 7¢, estimate the amount of money you would save each month by replacing all the 75 W incandescentbulbs in your house by 10 W flourescent ones. Be sure to clearly state your assumptions, since grading onthis problem will be mostly based on your reasoning, not on your answer.3. (From a homework set in a graduatecourse in synaptic physiology) As a resultof a complex set of biochemical reactions,the cell membrane of a nerve cell pumpsions (Na+ and K+) back and forth acrossitself, thereby maintaining an electrostaticpotential difference from the inside to theoutside of the membrane. Modifications ofthe conditions can result in changes inthose potentials.Part of the process can be modeled bytreating the membrane as if it were asimple electric circuit consisting ofbatteries, resistors, and a switch. A simplemodel of the membrane of a nerve cell isshown in the figure at the right. It consistsof two batteries (ion pumps) with voltagesV1 = 100 mV and V2 = 50 mV. Theresistance to flow across the membrane isrepresented by two resistors withresistances R1 = 10 K W and R2 = 90 KW. The variability is represented by aswitch, SW1.Four points on the circuit are labelled bythe letters a-d. The point b represents theoutside of the membrane and the point dthe inside of the membrane.. a What is the voltage difference across the membrane (i.e., between d and b) when the switch is open?. b What is the current flowing around the loop when the switch is closed?. c What is the voltage drop across the resistor R1 when the switch is open? closed?. d What is the voltage drop across the resistor R2 when the switch is open? closed?. e What is the voltage difference across the membrane (i.e., between d and b) when the switch is closed?. f If the locations of resistances R1 and R2 were reversed would the voltages across the cell membranebe different?4. Two small objects each with a net charge of Q (where Q is apositive number) exert a force of magnitude F on each other. Wereplace one of the objects with another whose net charge is 4Q.(i) The original magnitude of the force on the Q charge was F;what is the magnitude of the force on the Q now?(a)16F(b)4F(c)F(d)F/4(e)other(ii). What is the magnitude of the force on the 4Q charge?(a) 16F (b) 4F (c) F (d) F/4 (e) other(iii) Next, we move the Q and 4Q charges to be 3 times as far apart as they were. Now what is themagnitude of the force on the 4Q?(a) F/9 (b) F/3 (c) 4F/9 (d) 4F/3 (e) other(iv) In the original state (2 charges Q) if the symbol Q were taken to have a negative value, how would theforces change compared to the original state?(a) stay thesame(b) both wouldreverse(c) left onewould reverse(d) right onewould reverse(e) none of theabove.5. (From an exam) An internationalconsortium is presently building a deviceto look for anti-matter nuclei in cosmicrays to help us decide if there are galaxiesmade of anti-matter. Anti-matter is justlike ordinary matter except the basicparticles (anti-protons and anti-electrons)have opposite charge from ordinarymatter counterparts. (Anti-protons arenegative, and anti-electrons are positive.)A schematic of the device is shown at theright. A cosmic ray -- say a carbonnucleus or an anti-carbon nucleus --enters the device at the left where itsposition and velocity are measured. Itthen passes through a (reasonablyuniform) magnetic field. Its path is bent inone direction if its charge is positive, inthe opposite direction if its charge isnegative. Its deflection is measured as itgoes out of the device.. a On the figure shown, what is thedirection of the magnetic field? How do you know?. b What is the path followed by eachparticle in the device? Why?. c If you were given the magneticfield, B, the size of the device, D,the amount of charge on theincoming particle, q, and the massof the incoming particle, M, wouldthis be enough to calculate thedisplacement of the charge, d? Ifso, describe briefly how you woulddo it (but don't do it). If not, explainwhat additional information youwould need (but don't estimate it).RETURNSUniversity of MarylandPhysics DepartmentPhysics 122 HomeThis page prepared byEdward F. Redish Department of Physics University of Maryland College Park, MD 20742 Phone: (301) 405-6120 Email: [email protected] revision 27. February,