MSE HW3 Electrial, Optical, & Magnetic Properties

An 18 cm aluminum rod with an electrical resistivity of 18 ohm-cm and a 3 cm^2 cross-sectional area is cut into thirds (6 cm pieces). What is the electrical resistivity of each piece?

18 ohm-cm

What is the inverse of electrical resistivity?

Electrical Conductivity

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 250 V. The system must be able to move objects AT LEAST 100 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 only

Consider a 12 gauge (AWG) copper wire that is 3.31 cm long and has an electrical resistivity of 12x10-6 ohm-cm. What is the electrical resistance of the rod?

Correct answer:

12x10-4 ohm

If you apply a voltage to a piezoelectric material, it will:

change its shape

A capacitor initially uses a dielectric material with a dielectric constant of 12. If that dielectric layer is replaced with a new material having identical size to the initial material but with a dielectric constant of 4, what happens to the capacitance of the capacitor?

The capacitance will become 1/3 of the original capacitance.

Which two classes of materials properties are coupled in the piezoelectric effect?

Mechanical and Electrical

Which of the following BEST describes semiconductors?

Semiconductors switch between insulating and conducting states based on external signals (such as an applied voltage)

When a sufficient voltage (above the threshold) is applied to the gate of a MOSFET transistor...

Electrons can flow across the channel, completing the circuit, and the switch is "ON"

For magnetic storage materials, like those used in computer hard drives, permanent (remanent) magnetization is required for the memory storage. Magnetic fields are applied to "magnetize" each bit, but the magnetization should be switchable (from positive to negative) so that the memory bit can be "rewritten" when necessary. Consider the magnetization-magnetic field data for the four different magnetic materials reported below. Of these materials, which could sustain a permanent magnetization but could be re-magnetized to its opposite magnetization direction with the application of the LOWEST magnetic field possible.

Material C in the graph because it has the lowest coercive field, allowing the magnetization direction to switch when a lower field is applied

Refrigerator doors that support the attachment of magnets are made from:

Soft magnetic materials

True or False: The remanent magnetization of a material is its level of permanent, internal magnetization in no applied magnetic field.

True

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

A hard ferromagnetic material

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

Magnetization-Magnetic Field data for four different materials is reported in the figure shown here. Which material would be the BEST selection for fabricating the STRONGEST permanent magnet?

Material B in the graph becasuse it has the highest coercive field and highest magnetization when that field is applied

How would you categorize the magnetic behavior of oxygen, which has a VERY weakly attractive response to an external field, but no magnetization without an external field?

Paramagnetic

If you orient two linear polarizers such that they let through light waves with polarizations that are rotated 180° relative to one another, which of the following occurs? Assume that you are observing a light source with random polarization and that nothing is in between the two polarizers.

50% of light is transmitted

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

The material is dispersive and the prism has a specific shape

A new paint is designed to only reflect red light and absorb all other colors. What color would you perceive for an object that has been coated with this paint?

Red

How does waxing a car help make it "shine"?

The wax fills in surface asperities to increase specular reflection.

The angle at which light refracts when it enters the flat surface of a material could depend upon:

-refractive index of the material

-the wavelength of the light

-the angle of incidence

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%

The image with bending light going through an object is an example of?

Refraction

A thin, translucent plastic sheet appears green in color. Which of the following explanations may explain its appearance?

The plasic reflects green light and the plastic transmits green light

"Frosted windows"

...use surface roughness to scatter light and distort the image you see.