Republic of the Philippines

ROMBLON STATE UNIVERSITY

Odiongan, Romblon

College of Engineering and Technology

FINAL EXAMINATION

Name______________________________________________________Date_______________Score_____________

Materials Science and Engineering

Multiple Choice. Identify and select the correct answer that best completes the statement or answers the question. Write

the only on the blank space provided. Avoid erasures. (2 points each)

____ 1. Metals are good conductors of an electric current, which among its type has the highest electrical

conductivity of 6.8 x 10

a. Gold b. Silver c. Copper d. Aluminum

____ 2. The most widely used metallic conductor for electrical applications due to its ductility and electrical property

is.

a. Silver b. Copper c. Gold d. Aluminum

____ 3. Electrical conductivity is used to specify the electrical character of a material, its mathematical expression

is.

a. 1/ b. R/V c. 1/ d. V = I(l)

____ 4. This material has a high electrical resistivity, a resistance to oxidation at elevated temperature, a high melting

temperature and commonly used as heating elements.

a. Chrome-

Vanadium

b. Nickel-Chromium c. Brass d. Stainless

____ 5. An aluminum wire 5mm diameter and 5m long has a 0.04V potential drop across the end of the wire. What

is its current flow in ampere?

a. 4.0 b. 5.0 c. 6.0 d. 7.0

____ 6. As a solid absorbs energy in the form of heat, its temperature rises and dimensions increases. This response

of material due to the application of heat is called.

a. Thermal property b. Electrical property c. Magnetic property d. Optical property

____ 7. An indicative of a materials ability to absorb heat from the external surroundings; it represents the amount of energy required to produce a unit temperature rise is.

a. heat capacity b. specific heat c. heat transfer d. specific capacity

____ 8. At free expansion or contraction, the stress in the rod is.

a. > 1.0 b. - 1.0 c. 0 d. 1.0

____ 9. Upon heating, the stress induced in the material is called.

a. tensile b. shearing c. compressive d. bearing

____ 10. One of the uses of magnetic property of a materials is in electrical power generator, core winding materials

is considered as.

a. soft magnetic b. hard magnetic c. permanent magnet d. high coercivity

____ 11. A materials response to exposure to electromagnetic radiation and, in particular, to visible light is called. a. optical property b. thermal property c. magnetic property d. electrical property

____ 12. One of the applications of optical property of a material is in communication system through the development

of.

a. optical fiber b. copper wires c. data system d. glass wires

____ 13. It was made from silicon dioxide with high fluoride content and the best material for fiber optic technology

is called.

a. glass b. aluminum c. steel d. copper

____ 14. A material has optical property if it is.

a. reflective b. transparent c. opaque d. lustrous

____ 15. Which among from the choices is the application of magnetic property of a material in the system.

a. data hauling b. data storage c. data updates d. data printing

Problem Solving. Analyze and solve the problems correctly. Solutions are necessary to obtain maximum points in each

problem. Write your solutions answer on the reverse side of this paper. (10 points each)

16. If the magnetic field, H is generated by means of a cylindrical coil consisting of N, spaced turns, having a

length, l, and carrying a current of magnitude, I, compute the magnetic field strength in amperes per meter

on the tip of a screw driver in which a coil wire is 0.25m long, 400 turns and carries a current of 15 amperes.

17. The permeability, of a material is a measure of the degree to which the material can be magnetized, or the

ease with which a magnetic flux density, B field can be induced in the presence of an external H field.

Demonstrate that the relative permeability, and the magnetic susceptibility, are related to each other?

18. A steel wire is stretched with a stress of 70 MPa at 20 C. If the length is held constant, to what temperature

must the wire be heated to reduce the stress to 17 MPa? Linear coefficient of thermal expansion of steel, 12.0

x 10 / C.

Discussion. Explain or discuss the problem statement below. You may use extra sheets of paper for the answer. (5 points

each)

19. Briefly explain the manner in which information is stored and retrieved magnetically.

20. Explain why repeatedly dropping a permanent magnet on the floor will cause it to become demagnetized.

21. Discuss briefly how an optical fiber is advantageous on hauling of communication system?

22. An electric iron uses thermostat which regulates or controls the temperature of the heating elements. Discuss

a bimetallic strips regulates the temperature of an electric iron?

23. Explain how a fiber optic cable transmit data or signal through telephones systems, internet and cable TV?

Materials Science and Engineering Final2015

MULTIPLE CHOICE

1. ANS: B PTS: 2

2. ANS: B PTS: 2

3. ANS: A PTS: 2

4. ANS: B PTS: 2

5. ANS: C

I = V/R; 0.04V/R; R = L( )/A = L(1/ )/A; = 3.8 x 10

R = 5m * 4/(3.8x10 * * 0.005 m) = 6.7 x 10

I = 0.04V/6.7 x 10 = 5.97 A

PTS: 2

6. ANS: A PTS: 2

7. ANS: A PTS: 2

8. ANS: C

For free expansion or contraction, the rod will be stress free. If, however, axial motion of the rod is restrained

by rigid end supports, thermal stresses will be introduced.

PTS: 2

9. ANS: C PTS: 2

10. ANS: A PTS: 2

11. ANS: A PTS: 2

12. ANS: A PTS: 2

13. ANS: A PTS: 2

14. ANS: A PTS: 2

15. ANS: B PTS: 2

PROBLEM

16. ANS:

H = N*I/L H = 400*15/0.25 H = 24,000 A/m

PTS: 10

17. ANS:

= ; = ; B = ; B = ; M =

B = B; = ; = (1+ ) ; = - 1

PTS: 10

18. ANS:

Stress = 70Mpa - 17Mpa = -53Mpa (at this point the steel restraining the stress, under

compressive stress)

PTS: 10

OTHER

19. ANS:

Transference to and retrieval from the tape or disk is accomplished by means of an inductive readwrite head, which consists of a wire coil wound around a magnetic material core into which a gap is cut. Data are

introduced (or written) by the electrical signal within the coil, which generates a magnetic field across the

gap. This field in turn magnetizes a very small area of the disk or tape within the proximity of the head. Upon

removal of the field, the magnetization remains; that is, the signal has been stored. The same head may be

utilized to retrieve (or read) the stored information. A voltage is induced when there is a change in the

magnetic field as the tape or disk passes by the head coil gap; this may be amplified and then converted back

into its original form or character.

PTS: 5

20. ANS:

Repeatedly dropping a permanent magnet on the floor will cause it to become demagnetized because the

jarring causes large numbers of magnetic dipoles to become misaligned by dipole rotation.

PTS: 5

21. ANS:

Repeaters are typically the most expensive part of fiber optic systems, which becomes more significant

when distance and maintenance are considered. Existing submarine coaxial cables require repeaters every

5-8 km, which can be highly expensive to use. Typical optical fibers require repeaters every 50 km, which

leads to impressive savings.

PTS: 5

22. ANS:

A bimetallic strip consists of two different metals bonded together. The two metals should have a different

coefficient of expansion. If such a strip is heated, it starts to curve towards the metal having the lower

coefficient of expansion thus the supply of heat is temporarily stop. On cooling, it straightens and comes

back to the normal position which connects again to the supply to heat again the elements.

PTS: 5

23. ANS:

In order for the fiber optic to transmit data signals, it needs to be connected to the two other main components

of a fiber-optic system. The first of these is the optical transmitter, a device which converts electrical and

analog signals into either On-Off or Linear modulating light signals, then releases that data into the fiber

optic cable. The cable then relays the data emitted by the o optical transmitter to the optical receiver, which

accepts the light signal and reformats the data into its original form. PTS: 5