Homework #4 Magnetic, Optical, and Chemical Properties

True / False: Paramagnetic materials make good permanent magnets because they can achieve high magnetizations when placed in a magnetic field.

False

Paramagnetic materials are non-magnetic materials so when a magnetic field is applied there are negligible interactions.

True or False: If a hard magnetic material with a permanent magnetization at room temperature is heated above its Curie temperature and loses its permanent magnetization, that permanent magnetization will be regained once the material is cooled back to room temperature.

False

This type of material magnetizes when a magnetic field is applied and stays magnetized when the magnetic field is removed.

a) a soft paramagnetic material

b) a hard paramagnetic material

c) a soft ferromagnetic material

d) a hard ferromagnetic material

e) Both A & B

f) Both C & D

g) Both A & C

h) Both B & D

i) All of them (A, B, C, & D)

d) a hard ferromagnetic material

Using a UV/Vis spectrometer, it is found that a 0.5 cm thick piece of window glass reflects 12% of visible light (at 500 nm wavelength) and absorbs 4% of visible light (at 500 nm wavelength). How much light is transmitted through this glass at 500 nm wavelength?

a) 16%

b) 88%

c) 0%

d) 84%

e) 100%

f) 12%

g) It cannot be determined without knowing the refractive index of the glass at 500 nm.

d) 84%

A 1 cm thick piece of stainless steel metal is measured to reflect 98% of visible light at a wavelength of 500 nm. How much light is absorbed by the metal at a wavelength of 500 nm?

a) 2%

b) 100%

c) 98%

d) 0%

e) 1%

f) It cannot be determined without knowing the refractive index of the metal at 500 nm.

a) 2%

Why are the lenses of some sunglasses made from linear polarizers?

a) These polarizers make it easier to see images on screens that emit linearly polarized light.

b) Because the polarizer will block 50% of the light coming from the sun no matter which way you look at it.

c) Because light that reflects off of a surface (glare) has a preferential linear polarization, and these polarized lenses selectively block that portion of the reflected light.

d) Actually, linearly polarized lenses do not improve the performance of sunglasses, that is a marketing ploy!

c) Because light that reflects off of a surface (glare) has a preferential linear polarization, and these polarized lenses selectively block that portion of the reflected light.

Does the orientation of the linear polarizer in a sunglass lens matter?

a) Yes, the orientation of the polarizer is important in determining the performance of the sunglasses.

b) No, the polarizer can be in any orientation and provide the same overall performance to the sunglasses.

a) Yes, the orientation of the polarizer is important in determining the performance of the sunglasses.

When light enters a material and changes its direction of propagation, this process is called:

a) Reflection

b) Absorption

c) Refraction

d) It can be called either A or B.

e) It can be called either A or C.

f) It can be called either B or C.

g) Light never changes its direction of propagation when it enters a material.

c) Refraction

A thin, translucent plastic sheet appears blue in color. Based on this description, which of the following explanations may explain its appearance?

a) Both A & C could be valid explanations

b) The plastic absorbs blue light.

c) The plastic reflects blue light.

d) A, B, and C all could be valid explanations.

e) The plastic transmits blue light.

f) Both B & C could be valid explanations

g) Both A & B could be valid explanations

f) Both B & C could be valid explanations

True / False: In an electromagnetic wave of light, the electric field vector MUST BE perpendicular to both the magnetic field vector AND the direction of wave propagation.

True

Prisms are capable of separating white light into separate colors because:

a) The material used has a low refractive index.

b) The material used is dispersive.

c) The prism has a specific shape.

d) Both A & B

e) Both A & C

f) Both B & C

f) Both B & C

Which of the following approaches would NOT be useful for reducing galvanic corrosion between two pieces of different metals:

a) Requiring that the component only be used in dry, non-humid environments.

b) Completely painting one of the metals with a non-electrically-conducting plastic paint.

c) Placing a third metal in between the first two metals.

c) Placing a third metal in between the first two metals.

What is the "energy barrier" to diffusion?

a) The energy barrier to diffusion is the energy cost of entropically mixing all of the atoms up when they diffuse.

b) The energy barrier to diffusion is the energy cost of breaking bonds and disrupting the position of neighboring atoms to "squeeze" the diffusing atom from one site to another site.

c) Diffusion doesn't have an energy barrier, it is an athermal ("non-thermal") process.

d) The energy barrier to diffusion is the energy cost of atoms vibrating faster to push an atom from one site to another site.

b) The energy barrier to diffusion is the energy cost of breaking bonds and disrupting the position of neighboring atoms to "squeeze" the diffusing atom from one site to another site.

You are asked to help design a chemical purification process using diffusion of the impurities through a polymer membrane. The customer wants to reduce the time it takes to purify the chemical stream. What might you suggest to increase the rate of purification? (Note: "Free volume" is the amount of "open space" in a polymer.)

A. Switch to a polymer membrane with less free volume.

B. Switch to a polymer membrane with more free volume.

C. Raise the temperature of the process.

D. Lower the temperature of the process.

a) Recommend A only.

b) Recommend B only.

c) Recommend C only.

d) Recommend D only.

e) Recommend B & D.

f) Recommend A & C

g) Recommend A & D

h) Recommend B & C.

h) Recommend B & C.

More open space for diffusivity.

As temperature increases, D increases exponentially.

Which of the following best describes "anodization" of an aluminum part:

a) Electrically connecting the aluminum to a sacrificial anode.

b) Coating the aluminum with acrylic paint.

c) Electrochemically oxidizing the aluminum in a controlled manner.

d) Including additives in the aluminum's metallurgical composition prior to solidifying it.

e) Coating the aluminum with zinc.

c) Electrochemically oxidizing the aluminum in a controlled manner.

Which of the following approaches would be useful for improving a plastic's resistance to UV degradation?

A. Adding a UV absorbing coating to the plastic's surface.

B. Including additives to the plastic's composition that help prevent UV degradation.

C. Electrically connecting the plastic component to a sacrificial anode.

a) A only

b) B only

c) C only

d) All of the above (A, B, and C)

e) Both A and C

f) Both B and C

g) Both A and B

g) Both A and B

Which of these elements is/are known to form self-limiting oxide surface layers that are protective against further corrosion:

A. Iron

B. Aluminum

C. Chromium

D. Copper

a) D. Copper Only

b) C. Chromium only

c) Both B and C.

d) B. Aluminum only

e) Both A and D

f) A. Iron only

g) B, C, and D

h) All of these (A, B, C, and D)

i) None of these.

c) Both B and C.

(Aluminum and Chromium)

True/False: In steady state, dilute species in a solid USUALLY diffuse from regions of HIGH concentration to regions of LOW concentration.

True