S 16Exam 2Phys 1220 makeup
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name
Each problem is of equal value.
You can skip two problems according to the following rules:
You can skip one of problems 1, 2, and 3.
You can skip one of problems 4, 5, and 6.
If you work more than 4 problems, we will grade all and count the best results consistent with the above rules. Make sure you work and review first all required problems before you start to work extra problems!
Tips for better exam grades:
Read all problems right away and ask questions as early as possible.
Make sure that you give at least a basic relevant equation or figure for each sub-problem.
Make use of the entire exam time.
Show your work for full credit. The answer ‘42’ only earns you any credit IF ‘42’ is the right answer. We reserve points for ‘steps in between’, figures, units, etc. If all you give us is a numeric answer you may receive only a C grade for the problem and in some cases even less.
No credit given for illegible handwriting or flawed logic in an argument.
Multiple choice problems may have more than one correct answer. Full credit only for marking all answers correctly as true or false and for explaining the reasoning why the answer is true or false.
- RC Circuits
a)Derive and solve the differential equation for discharging a capacitorthat is in series with a resistor R as a function of time.
Hint: Use Kirchhoff Rules to find your starting point
b) Consider an experiment in which you have one resistor, R = 10,000 [], and one capacitor, C = 100 [nF] across a source of = 100[V].
What is the charge of the fully charged capacitor?
After how much time will the capacitor be half charged?
c) Consider an experiment in lab where you measure charge and time. Determine via error propagation (also known as error progression) what the uncertainty in the current is at the time when the capacitor is half charged. Assume that all quantities are known to .
2.Kirchhoff Rules
A-Explain the Kirchhoff Rules and explain based on currents and potential differences why they are valid.
B-What are the currents through each resistor and in which directions do they flow (see figure below)?
C- Consider the circuit in the figure being used in lab. What is a leading systematic error and what is a leading random error in measuring the currents in this circuit?
n/b: Full credit is only given, if you use the Kirchhoff Rules and show the steps of your calculation. Operator errors are categorized neither as random nor as systematic error.
3. Capacitor Networks and Energy Storage
Consider the capacitor network shown below :
A- Find Ceq.
B- How much energy is stored in the 12 [F] capacitor between potential points e and f?
4. Magnetism: Field and Force due to Moving Point Charges
Each of the lettered points at the corners of the cube represents a positive charge q moving with a velocity of magnitude ‘v’ in the direction indicated.
Hint: charge d moves along the space diagonal of the cube.
A- What is the direction of the magnetic fields on each charge due to charge c?
Hint: show your work for partial credit. Matrixes/determinants receive only credit, if the final result is correct.
B- What is the direction of the force on each charge due to the field from charge c?
Hint: show your work for partial credit. Matrixes/determinants receive only credit, if the final result is correct.
5. Magnetic Field due to Current Carrying Straight Wires
a)What are thenet magnetic field strengths and directions,Bnet ,at a point half way between wire 1 and wire 2 and half way between wire 2 and wire 3?
b)Rank the net magnetic force per length magnitudes on the three wires due to the respective other two wires. In which directions do the net forces point?
Show your work for full credit. Assume that the wires are infinitely long.
6.Magnetic Fields and Magnetic Forces
Which of the following statements about uniform and non-uniform magnetic fields are true?
For full credit, mark all statements as true or false and explain briefly your reasoning in the space below each statement.
A)The net magnetic force on a current loop in a non-uniform magnetic field is zero.
B)A moving charge that is in the presence of a magnetic field does always experience a magnetic force.
C)A moving electric charge produces magnetic fields everywhere in space.
D)Magnetic force can be parallel to the magnetic field that causes the force.
E)Current carrying wires produce non-uniform magnetic fields in their neighborhood.
F)is not always true.
Master Equations Phys 1220
Capacitor charging
and and
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near a long straight wire and
Need to put your mind off the test for a minute? Check this out:
Jay Leno: What are magnets?" A taxi driver: "Are they the things crawling over a week-old dead cat?"
Jay Leno: Which is more useful, the Sun or the Moon?" A thirteen-year old: [Pause] "I think it's the Moon because the moon shines at night when you want the light, whereas the Sun shines during the day when you don't need it."
A man, complaining of headaches, entered a hospital for diagnostic tests. A doctor examined the results for a brain scan and told the patient, "I have bad news and good news for you. The bad news is that you have a serious brain disease and will die without treatment. The good news is that this hospital has developed a new procedure for brain transplants and due to a car accident this morning two 'fresh' brains are available: one is from a taxi driver and the other is from a scientist. The brain of the taxi driver costs $225,000, while that of the scientist is only $29.95." Puzzled, the patient asked, "Why is the scientist's brain was so much cheaper?" The doctor replied, "It's used."
Who said it? (Answers at the bottom)
It is not enough to have a good mind. The main thing is to use it well.
Mathematics is written for mathematicians.
The lecturer should give the audience full reason to believe that all his powers have been exerted for their pleasure and instruction.
Physics is experience, arranged in economical order.
Don't cry because it's over, smile because it happened.
Live as if you were to die tomorrow. Learn as if you were to live forever.
(Rene Descartes, Copernicus, Michael Faraday, Ernst Mach, Dr.Seuss, Mahatma Gandhi)