My Students' Section

CHAPTER EXAM ON WORK AND ENERGY (given last 10-05-09)

2009-10-09T23:41:00.000-07:00

ANSWER AS REQUIRED: Show your solution(s) neatly and legibly.

1. Discuss whether any work is being done by each of the following agents and, if so, whether the work is positive or negative: (a) a chicken scratching the ground, (b) a person studying, (c) a crane lifting a bucket of concrete, (d) the gravitational force on the bucket in part (c),(e) the leg muscles of a person in the act of sitting down.

Answer(s):

(a.) zero work. Relative to the ground, the direction of the force applied by the chicken is perpendicular, thus zero work done.
(b.) zero work. Literal meaning of work is different in physics.

(c.) positive work. Force on the crane is in the same direction of the displacement of the bucket of concrete.

(d.) negative work. The direction of the displacement is ant-parallel with the gravitationalforce.

(e.) zero work. Relative to the muscle, zero displacement.

2. Batman, whose mass is 80.0 kg, is dangling on the free end of a 12.0-m rope, the other end of which is fixed to a tree limb above. He is able to get the rope in motion as only Batman knows how, eventually getting it to swing enough that he can reach a ledge when the rope makes a 60.0° angle with the vertical. How much work was done by the gravitational force on Batman in this maneuver?

3. A 700-N Marine in basic training climbs a 10.0-m vertical rope at a constant speed in 8.00 s. What is his power output?

Answer:

4. A 6.0-kg block initially at rest is pulled to the right along a horizontal surface by a constant horizontal force of 12 N. Find the speed of the block after it has moved 3.0 m if the surfaces in contact have a coefficient of kinetic friction of 0.15. The surface is no longer frictionless.

2006-01-11T23:26:00.000-08:00

A problem on Electric Potential calculations at pt. B

2005-10-05T04:22:00.000-07:00

Physics 11 A1 Final Exams
Mindanao Polytechnic State College
School of Arts and Sciences

I. Multiple choice. Write the letter of the correct answer on the space provided for.

1. The following is a unit of inductance except
a. Wb/A b. T.m2/A c. J/A2 d. Ω2/V
2. Two current carrying wire is placed are closely placed together. If the direction of the two current is opposite, the two wires will
a. attract b. repel c. rotate d. no interaction
3. Which of the following does not cause electromagnetic induction?
a. changing magnetic flux b. changing magnetic field c. changing area d. changing electric flux

4. The magnetic field at a distance R, due to the current in the very long wire, varies with distance R according to
a. R-2 b. R-1 c. R1 d. R2
5. What is the value of the induced emf if the wire loop moves with velocity v as shown in the figure?
a. 0 b. 2πrvI c. I/2πrv d. 2πrv/I
6. What is the magnetic field produced by a particle with charge q moving with velocity v at a distance R in front of the particle?
a. O b. (µoqv)/(4πR2) c. (µoqv4πR2) d. 4R2/(µoqv)
7. A current-carrying wire is placed between the poles of a magnet as shown in the figure below. What is the direction of the force on the wire?
a. up b. down c. left d. right
8. If a current is traveling toward you in a wire, what is the direction of the magnetic field?
a. clockwise b. counterclockwise c. away from you d. towards you
9. If the current in the inductor increases, what is the induced current in the inductor will
a. increase, its direction is opposite to the applied current
b. decrease, its direction is opposite to the applied current
c. increase, its direction is along the direction of the applied current
d. decrease, its direction is along the direction of the applied current
10. Ampère's law is valid
a. when there is a high degree of symmetry in the geometry of the situation.
b. when there is no symmetry.
c. when the current is constant.
d. for all of these conditions.
11. An observer moves past a stationary electron. His instruments measure
a. an electric field only c. both the electric and magnetic fields
b. a magnetic field only d. any of the choices, depending on his speed
12. Which of the following is NOT TRUE?
a. Faraday’s law can be used to calculate magnitude of induced emf.
b. Lenz law can be used to calculate magnitude of induced current.
c. Faraday’s law can be used to calculate electric fields induced by changing magnetic flux.
d. Lenz law gives an alternative way of determining the direction of induced current.
13. Inside the region, the magnetic force on the electron is always _______ to its while the electric force is always _______.
a. perpendicular, parallel b. parallel, perpendicular
c. pependicular, downward d. parallel, upward
14. In the presence of the uniform magnetic field, the electron would follow what path?
a. upward b. parabolic
c. straight-line d. circular
15. If two wires in free space at a distance d apart and each carries a current in opposite direction, the force each wire exert on the other is
a. Repulsive b. attractive
c. depends on the magnitude of each current d. depends on the distance between the two wires.
16. What is the magnetic field at the center of the two concentric arcs? The inner arc is of radius 4cm and the outer arc is of radius 6cm. The loop carries a current of 4A.
a. 3.49 x 10-6 T b. 7.14 x 10-4 T c. 4.45 x 10-5 T d. 2.09 x 10-5 T
17. The magnitude of the magnetic force acting on a particle in a region of magnetic field is
a. independent of its charge b. proportional to its speed
c. parallel to the magnetic field d. perpendicular to the magnetic field
18. A circular coil of 50 turns and radius 5.0cm is placed with its plane oriented at 900 to a magnetic of 0.1 T. The field is now increased at a steady rate, reaching a value of 0.5T after 2 seconds. The induced emf in the coil is
a. 0.118 V b. 0.225 V c. 0.098 V d. 0.079 V
19. A positive charge q is moving with a velocity at an angle 300 with the magnetic field B. The magnitude of the magnetic force is
a. qvB/2 b. qvB3/2 c. 2avB d. zero
20. What is the property of a substance to attract pieces of iron and steel?
a. Permeability b. Resistivity c. conductivity d. Magnetism

Part II. Discussions:

1. Discuss the different magnetic properties of the materials based on the effect of the external magnetic field on the internal magnetic field of the materials

2. What is the heart of the course “Electromagnetism” ? Discuss briefly the four Maxwell’s equations.

Part III. Problem Solving

Problems: Show all your solutions neatly.

1. Given the conductor above. Determine the magnetic field at regions
a. r < R
b. R < r < 2R
c. r > 2R
2. If a rectangular loop is placed in parallel with an infinite current carrying wire. Find the net magnetic force acting on the rectangular loop.

BONUS PROBLEM Find the induced emf on the conducting loop. If the loop is moving with velocity v to the right.

** END OF THE EXAM **

Goodluck, Happy Summer and God Bless!!!

Summer Classes' Midterm Exam

2005-05-06T04:54:00.001-07:00

Mindanao Polytechnic State College
School of Arts and Sciences, PHYSICS DEPARTMENT
Phys 11 Midterm Examination
Summer 2005

Part 1. MULTIPLE CHOICE.
Direction: For each analytical problem, show first your solution systematically then write the CODE that matches to the best answer on your test booklet. NO COMPUTATIONS SHOWN, NO CREDIT TO THE CORRECT CHOICE. If your answer is not among the given choices, write down the correct one.
1. When a slab of insulating material is placed between the plates of a charged capacitor, the electric field there relative to what it was before is
(czar) less (zarc) more (arcz) the same (rcza) any of the above, depending on the circumstances.
2. An electric charge
(char) is a continuous quantity that can be subdivided indefinitely
(harc) is a continuous quantity but it cannot be subdivided into smaller parcels than 1.6 x 10 –19 C
(arch) occurs only in separate parcels, each of 1.6 x 10 –19 C
(rcha) occurs only in separate parcels, each of 1.0 C
3. Capacitors in parallel combination:
(pglo) store less energy than when the capacitors are in series arrangement.
(glop) store more energy than when the capacitors are in series arrangement.
(lopg) store the same amount of energy as when capacitors are in series.
(opgl) has energy storage that depends on the equivalent capacitance.
4. Two small plastic spheres are given negative electrical charges. When they are 40cm. apart, the repulsive force between has a magnitude of 0.20N. What are the charges on each sphere if one has twice the charge of the other?
(sphr) 0.87 & 1.7 μC (phrs) 1.22 & 2.5 μC (hrsp) 1.33 & 2.7 μC (rsph) 1.70 & 3.4 μC
5. Two Gaussian surfaces A1 and A2 are located near each other. If the the only charge present is Q at the center of A1, which of the following statement is not true.
(gaus) The net flux thru A1 is equal to Q/Єo
(ausg) The no. of electric field lines entering A2 also leaves A1.
(usga) The net flux thru A2 is equal to the net flux thru A1.
(sgau) The net flux thru A2 is equal to zero.
6. The electric field at a point is equal in magnitude to
(cost) the number of electric field lines that pass through the point
(ostc) the electric charge there
(stco) the force a charge of one coulomb would experience there
(tcos) the force an electron would experience there
7. Two charged particles having charges q1 = 0.50nC and q2 = 8.0nC are separated by a distance of 1.20 m. At what point along the line connecting the two charges is the total electric field due to the two charges equal to zero?
(fiel) 0.24 (ielf) 0.35m (elfi) 0.53m (lfie) 0.60m
8. Which of the following statements is NOT TRUE for a conductor?
(radi) In electrostatic conditions, the electric field is zero inside a conductor.
(adir) There is no current within a conductor if E is zero because the charges are not moving.
(dira) Given a uniform electric field inside a conductor, there is a steady force F=qE on the charging side of the conductor causing it to attain motion.
(irad) The moving charges on metal conductors are electrons only.
9. The potential at a distance of 25.0 cm from a very small charged sphere is 48.0V, with potential taken to be zero at an infinite distance from the sphere. If the sphere is treated as a point charge, what is the potential at a distance of 75.0 cm from the sphere?
(volt) 12.0 V (oltv) 14.0 V (ltvo) 16.0 V (tvol) 20.0V
10. If a 20 μC capacitor is to have an energy content of 2.5 J, it must be placed across a potential difference of
(acro) 150 V (croa) 350 V roac) 500 V (oacr) 250 kV
11.In Coulomb's law, the magnitude of electrical force of attraction between two point charges is directly proportional to the
(phys) sum of the charges (hyps) product of the charges
(shyp) product of the distance (pshy) square of the distance
12.Which of the following is TRUE for a parallel-plate capacitor?
(sss) There is no associated potential energy in moving a test charge between two points in the conducting plates of a parallel-plate capacitor.
(gsis) Capacitance of a parallel –plate capacitor need not be dependent on the area of the conducting plate.
(dost) The dielectric constant κ varies for every kind of material used as dielectric or material placed in between plates of a capacitor.
(ched) The capacitance of a capacitor in the presence of a dielectric material is the same as that when the capacitor is in vacuum.
13.How many 2.0 uF would have to be connected in parallel to store 10-4 C of charge with a potential difference of 5V across each?
phys) 5 (shyp) 10 (hyps) 50 pshy) 100
14. A spherical Gaussian surface surrounds two oppositely charged particles of equal magnitude. Which of the following statements is correct?
(phys) The net electric flux is zero.
(shyp) The net electric flux is directed outward of the Gaussian surface
(hyps) The net electric flux is directed into the Gaussian surface
(phys) There is no electric field inside the Gaussian surface.
15. How many 2.0V resistors would have to be connected in series to have a current of1.0A when a potential difference of 10-V is put across the network? (phys) 5 (shyp) 10 (hyps) 50 (phsy) 100
16.In a given region the electric field is constant and has a value of 100 V/m. It points in thee positive x-direction. If the potential at the point x=4 cm on the x-axis is 6 V, what would be the potential at the point x=16 cm? (phys) -22 v (shyp) -18 v (hyps) -10 v (phys) -6 v
Items 17 & 18. The emf and the internal resistance of the battery are shown.

12 v 2 V
a b
Figure 2

17.In figure 2, a current of 6 A is drawn from the battery. The terminal voltage of the battery Vab is closest to: (phys) zero (shyp) +12 (hyps) +24 (phys) -12
18.In figure 2, a 3V cable is connected across the battery. The rate at which chemical energy in the battery is depleted is closest to
(phys) 24 W (shyp) 27 W (hyps) 29 W (phys) 32 W
19.If the length and diameter of a wire of circular cross section are both doubled, the resistance is
(phys) unchanged. (shyp) increased fourfold. (hyps)doubled. (phys) halved.
20.The unit of electric field is N/C. An equivalent unit is:
(unit) V.m (nitu) V/m (itum) Vm2 (tumi) V/m2
21.A three-series capacitors has an equivalent capacitance of 5.0mF. If the two capacitors have values of 12mF and 30mF, the third capacitor has a value of
(svdb) 5mF (vbds) 10mF (bdsv) 12mF (dsvb) 15 mF
22.A positive charge resides at the origin while a 2.0-nC charge is 3.0 mm from it. What must be its magnitude such that it experiences a force of 10 N?
(acdb) 2.0 nC (bdca) 5.0 mC (cbda) 0.7 C (dbca) 6.0 nC
23.Which of the following statements is false?
(acdb) When a negative charge moves in the direction of an electric field, the field does negative work and the potential energy increases.
(bdca) When a negative charge moves in the direction opposite to an electric field, the field does positive work and the potential energy increases.
(cdba) When a positive charge moves in the direction of an electric field, the field does positive work and the potential energy decreases.
(dbca) When a positive charge moves in the direction opposite to an electric field, the field does negative work and the potential energy increases.
24.Three equal point charges of 100 nC are placed at the corners of an equilateral triangle whose side is 1.0 m. What is the electrical potential energy of the system? Take as zero the potential energy of the system when they are infinitely far apart.
(adbc) 6.75 mJ (bdca) 0.27 mJ (cdba) 1.35 mJ (dabc) zero
25.Which of the following the correct magnitude of the electric field that by an infinite line of charge?
(adbc) E= σ/2ε0 r2 (bdca) is proportional to 1/r2 (cabd) E=λ/2π ε0 r (dabc) zero
26.The energy content of a charged capacitor is carried by the
(adbc) charges on the plates (bcda) electric field between the plates (cbda) plates dbca) dielectric
27. Which of the following is false?
(acbd) Ohm's law is only an approximate description of the response of materials to electric field.
(bacd) Ohm's law states that the current density through a material increases linearly with the applied voltage.
(cbad) Ohm's law gives a description of the electrical properties of all materials
(dbac) Ohm's law does not hold for conductors.
Items 28, 29 & 30 refer to figure 28.
28. The equivalent resistance of the network is
(wxyz) 0.5V (xyzw)0.25V (yzwx) 2.0V (zwxy)4.0V
29. If a battery of 12V is placed across the network xy, the current through the 2.0V resistor is
(swan) 2.0A (wans) 3.0A (answ) 4.0A (nswa) 6.0A
30. If a battery of 12.0V is placed across the network xy, the potential drop across the 1.5V
resistor is
(rest) 1.5V (estr) 3.5V (stre) 4.5V (tres) 7.5V
Part II. PROBLEM-SOLVING: Solve each problem logically and show your solution/s legibly.
A. A parallel-plate capacitor has a 7.0 J of energy stored in it. The separation between the plates is 2.0mm. If the separation is
decreased to half of the original distance, what is the energy stored if:
31) the capacitor is disconnected from the potential source, so that the charge on the plates remains constant?
32) the capacitor remains connected to the potential source so that the potential difference between the plates remains constant?
C. Three equal point charges of q = 8.4x10-7C are placed at the corners of an equilateral triangle whose side is 1 m.
33) What is the potential energy of one point charge due to the other two charges?
34) What is the total potential energy of the system? (take as zero the potential
energy of the three charges when they are infinitely far apart.)
D. A capacitor network.
35) Find the equivalent capacitance of the combination as shown in Figure 3; and,
36) Find the charge of C1

The Quiz Show Mechanics: Rules and Guidelines for my Phys 11 "Electromagnetism" Class

2005-03-08T20:42:00.001-08:00

Quiz Show Mechanics

RULES AND GUIDELINES

1. The quiz show shall comprise of six(6) groups. Each group shall have a teaam captain to be chosen according to their performance of the physics 11 course.

2. The role of the team captain is to represent their respective group. He/she shall present the answer of his/her group in a form of a report.

3. the members of the group that first to present shall be informed will about the answer they shall be presenting.

4. the groups other than the one, which currently presents their answer, can raise question, either hypothetical or real, to any members of the presenting group only after the report is being completed.

5. the quetioning group shall decide who among the members of the presenting group should answer their question.

6. the member of the presenting group, whom the other group has asked the question with, shall answer without the help of the other co-members.

7. failure to answer the question means a chance for the questioning group to answer, first to their question, and then to present their solution to the main problem.

8. the rest of the groups shall again listen to the next presenting group. When there will be no other questions for the presenting group, then the latter shall have the most points for that particular problem.

9. Only the first three among all groups shall present their answer. The rest of the groups shall have to steal the chance to present before having the third presenting group otherwise most of the points would go to the latter.

SCORING:

1. the presenting group having mentioned in no. 7 R and G shall have 20 points for problems that need to be solved for not less than 10 minutes. And shall obtain 10 points for other problems that require one or two steps solutions.

2. the groups other than the one mentioned above shall have 10 points for not less than 10 minutes calculations, and 5 points otherwise.

Prepared by: Tompong, Marichu M.
Physics 11 Instructor

Derivation of the BOSE-EINSTEIN Distribution...

2005-02-19T02:22:00.000-08:00

Just post this one bcoz I need this in my prob set in masteral...

The MIDTERMS...

2005-02-18T04:55:00.000-08:00

-still on process-