MSE 2001 Homework 2 & 3: Thermal, Electrical, Optical, and Magnetic Properties

A 1 cm thick piece of silver stainless steel metal it measured to reflect 95% of visible light. How much light is transmitted through the metal?

0%

For a 1 cm thick piece of transparent window glass, it is found that 8% of incident light is reflected and 2% of incident light is absorbed. How much light is transmitted?

90%

True or False: Electrostriction is when you apply an electric field to a material and the material's length changes.

true

True or False: The remanent magnetization of a material is its level of permanent, internal magnetization.

true

Consider sitting in the front seat of a car. The visible light reflected off of the car's hood is A. ...preferentially polarized. B...of the color (wavelength) that you perceive your car as being. C. ...randomly polarized. D. a&b E. b&c F. none of the above

D

The materials property that describes the amount of heat energy STORED for a given temperature differential is the: a)thermal diffusivity b)CTE mismatch c)heat flux d)thermal conductivity e)heat capacity

e

What is the inverse of electrical conductivity?

electrical resistivity

You are asked to help design the thermal expansion joints for a bridge. The bridge will have one joint on both sides of the bridge where it connects to the earth. Assume that the earth does not move with temperature fluctuations (not the best assumption, but let's go with it!). The bridge is 100 m long and will be manufactured from a steel with a thermal expansion coefficient of 10 ppm/°C. All manufacturing will be in an indoor facility kept at 25 °C. Assume that once installed the bridge may see temperature fluctuations from -30 °C to +45 °C. What should be the minimum gap size for the thermal expansion joints? (Recall you have two joints.)

i cm

When looking through a linear polarizer at a light source producing randomly polarized light... A. The light intensity will fluctuate between 100% and 50% as the polarizer is rotated 360°. B. The light intensity will fluctuate between 100% and 0% (no light) as the polarizer is rotated 360°. C. The light intensity will fluctuate between 50% and 0% (no light) as the polarizer is rotated 360°. D. The light intensity will be the same as the original light source and remain constant as the polarizer is rotated 360°. E. The light intensity will constantly be reduced by 50% as the polarizer is rotated 360°.

E

Which of the following is NOT an example of a degradation mechanism caused by a chemical reaction? A. Burning of a plastic component B. Rusting of a steel component C. Degradation of a plastic component when exposed to sunlight. D. Galvanic corrosion of a steel bolt threaded through a nickel sheet. E. Degradation of a plastic component when exposed to acetone.

E

You work for a manufacturing facility that produces electrical resistors. Currently you sell a resistor that has a length of 9 cm, a cross-sectional area of 3 cm2 and uses Metal A with an electrical resistivity of 2 ohm-cm. Unfortunately the melting point of the resistive metal is too low and these resistors keep failing due to melting in operation. You are asked to design a new resistor with the same resistance using Metal B which has a higher melting temperature. Metal B has an electrical resistivity of 3 ohm-cm. What would you recommend for its design? length: area:

2cm, area 1cm^2

A metal rod with a square cross-section has a resistance of 8 ohms. If the square edge has a width of 2 cm and the rod has a length of 4 cm, what is the resistivity of the metal?

8 ohm-cm

An example of galvanizing steel is which of the following: A. Coating the steel with zinc. B. Electrically connecting the steel to a sacrificial anode. C. Coating the steel with acrylic paint. D. Electrochemically oxidizing the steel in a controlled manner. E. Including additives in the steel's metallurgical composition prior to solidifying it.

A

*****You are designing a system based on piezoelectric actuation to precisely move objects at the nanometer scale. Your system is limited to an operating voltage of 500 V. The system must be able to move objects at least 150 nm. You are allowed to select amongst the following piezoelectric materials in the table below to accomplish this mechanical motion. Which of these materials would you recommend for this mechanical manipulation system? Material I: d33 = 100 pm/V Material II: d33 = 200 pm/V Material III: d33 = 400 pm/V Material IV: d33 = 1000 pm/V A. III and IV B. III only C. IV only D. II, III, and IV E. all will work F. none will work

A. III and IV

If you wanted to maximize the deflection of a bimetallic strip undergoing a temperature swing of 10 °C which two materials amongst the 4 listed below would you choose? (Assume the elastic properties are identical for all materials.) Material A, heat capacity = 5 J/g-°C, thermal expansion coefficient = 5 ppm/°C Material B, heat capacity = 3 J/g-°C, thermal expansion coefficient = 3 ppm/°C Material C, heat capacity = 10 J/g-°C, thermal expansion coefficient = 15 ppm/°C Material D, heat capacity = 15 J/g-°C, thermal expansion coefficient = 10 ppm/°C A. b&c B. a&c C. a&b D. c&d E. b&d

A. b&c

******The angle at which light refracts when it enters the flat surface of a material could depend upon: I. The refractive index of the material. II. The wavelength of the light. III. The size of the material. IV. The angle of incidence of the light into the material. A. I, II, & III B. I, II, & IV C. I & II D. I E. I & IV F. II

B

Steel beams to be used for outdoor construction are going to be electroplated with a corrosion-protection coating. Steel has a thermal expansion coefficient (\alphaα) of 13 ppm/°C. Which of the following coating materials would you select to minimize risk of thermal delamination of the coating? A. Super coating (5ppm C) B. Ultra Coating (12 ppm C) C. Mega Coating (15 ppm C) D. Optima Coating (0ppm C)

B

Which of the following approaches would NOT be useful for improving a plastic's resistance to UV degradation? A. Including additives to the plastic's compositional formulation. B. Using cathodic protection. C. Adding a coating to the plastic's surface D. Selecting a proper material

B

Compared to a building with walls of wood, a building with walls of bricks is more energy-efficient in maintaining its internal climate with the temperature swings of the day because.... A. The brick's lower heat capacity allows it to absorb less heat during the hot parts of the daytime and then release that heat for shorter times throughout the cool nights. B. The brick's lower thermal conductivity allows it to absorb more heat during the hot parts of the daytime and then release that heat for longer throughout the cool nights. C. The brick's higher thermal conductivity allows it to absorb more heat during the hot parts of the daytime and then release that heat for longer throughout the cool nights D. The brick's higher heat capacity allows it to absorb more heat during the hot parts of the daytime and then release that heat for longer throughout the cool nights. E. The brick's lower heat capacity allows it to absorb more heat during the hot parts of the daytime and then release that heat for longer throughout the cool nights. F. The brick's lower thermal conductivity allows it to absorb less heat during the hot parts of the daytime and then release that heat for shorter times throughout the cool nights.

D

You work for an electronics manufacturer and are asked to design a new capacitor. The capacitor has a basic parallel plat design, so the dielectric layer will be a "flat" square. Assuming the capacitor must be a fixed area and it must be as thin as possible (because it will be placed in the newest slim-design cell phone), which of the following materials would you recommend? A. Blue-Gold Charge Separator Dielectric Constant: 25 Electrical Resistivity: 100 giga-ohms-meters B. The Burdell Special Dielectric Constant: 15 Electrical Resistivity: 100 giga-ohms-meters C. Buzz Storage Plus Dielectric Constant: 15 Electrical Resistivity: 150 giga-ohms-meters D. GT Charge Master Dielectric Constant: 25 Electrical Resistivity: 150 giga-ohms-meters

D

This type of material magnetizes when a magnetic field is applied and stays magnetized when the magnetic field is removed. a)soft paramagnetic material b)hard paramagnetic material c)soft ferromagnetic material d)hard ferromagnetic material e)both a&c f)both b&d

D: hard ferromagnetic

Anodization of aluminum can be used to do all of the following EXCEPT: A. Protect against corrosion. B. Change the color of aluminum. C. Make the surface harder. D. Both a&b E. Anodization can be used to do all three of these (A, B, and C)

E

What is the proportionality constant that determines the amount of magnetization that occurs within a material when a magnetic field is applied to the material? A. Paramagnetic Constant B.Ferromagnetic Constant C.Magnetic Moment D.Magnetic Permittivity E.Magnetic Susceptibility

E. magnetic susceptibility

A capacitor initially uses a dielectric material with a dielectric constant of 5. If that dielectric layer is replaced with a new material having identical size to the initial material but with a dielectric constant of 10, what happens to the capacitance of the capacitor? A. It is impossible to predict how the capacitance will change with the information provided. B. The capacitance will be cut in half. C. The capacitance will not change because it is an inherent property of the material. D. The capacitance will become 1/5 of the original capacitance. E. The capacitance will increase by a factor of 10x. F. The capacitance will become 1/10 of the original capacitance. G. The capacitance will double in size.

G

Materials A, B, and C have the thermal properties listed below. You are asked to choose the best material for a cooking pot. For this application, you want to optimize the speed to thermalize the material--i.e., rate to reach equilibrium temperature with heat source. Which material(s) would you recommend? Material A: Thermal Conductivity = 10 W/m-K Heat Capacity = 5 J/m^3-K Material B: Thermal Conductivity = 9 W/m-K Heat Capacity = 3 J/m^3-K Material C: Thermal Conductivity = 10 W/m-K Heat Capacity = 4 J/m^3-K A. material a B. material b C. material c D. material a&b would be equally good

b

The materials property that determines the amount of heat flux that will flow across a given length of material at a fix temperature difference is the: a)heat capacity b)thermal diffusivity c)thermal conductivity d)thermal expansion coefficient e)thermal flux capacitance

c) thermal conductivity

True or False: As long as a component's operation temperature remains below the melting temperature of all materials in that component, it will not fail.

false

True or False: If a hard magnetic material is heated above its Curie temperature and then cooled back to room temperature it will regain its original permanent magnetization.

false