7 Multiple Choice Questions 1If two materials have Rockwell

7: Multiple Choice Questions:                                                                                                            

1.If two materials have Rockwell Scale C hardness of 50 and 58 respectively,

a)We can’t tell which one is harder.

b)We know that the material with Rockwell C scale reading of 50 is harder.

c)We know that the material with Rockwell C scale reading of 58 is harder.

2.Hardness of steel has an excellent correlation with tensile properties of steel. Hardness testing is often conducted because:

a)A good understanding of tensile properties of steel helps in determining manufacturing processes to use

b)Hardness value helps in determining tools to use during machining.

c)Hardness testing is generally easier and cheaper than tensile testing

d)All of the above.

3.Thermal conductivity is a physical property of a material which describes:

a.     The ability of a material to transfer heat along its length, width and thickness

b.    The ability of a material to absorb heat

c.     The ability of a material to emit heat by radiation

d.    A measure of the temperature rise of a unit volume of material per unit heat input

e.     None of the above

4.Ductility of a metal is described quantitatively by:

a.     The change of volume of a material as it is subjected to a hydrostatic pressure

b.    The overall change in length of a test rod which has been subjected to a constant load

c.     The overall reduction in the cross sectional area of a test rod which has been subjected to a constant load

d.    The amount of plastic deformation the material receives in a tension test to failure

e.     None of the above

8: Indicate whether the following are true or false

T F             A material’s chemical property could be described as it’s reaction with other chemicals (gases, liquids and solid materials).

T F             Tensile strength is a measure of a material’s resistance to being pulled apart.

Solution

1. Material with Rockwell C scale reading of 58 is harder. Therefore, answer is c.

2. All options are correct.Therefore, answer is d.

3. Thermal conductivity (often denoted k, , or ) is the property of a material to conduct heat. It is evaluated primarily in terms of Fourier\'s Law for heat conduction.Heat transfer occurs at a lower rate across materials of low thermal conductivity than across materials of high thermal conductivity. Correspondingly, materials of high thermal conductivity are widely used in heat sink applications and materials of low thermal conductivity are used as thermal insulation. The thermal conductivity of a material may depend on temperature. The reciprocal of thermal conductivity is called thermal resistivity.

Materials with a high thermal conductivity constant kkk (like metals and stones) will conduct heat well both ways; into or out of the material. So if your skin comes into contact with metal that is colder than your skin temperature, the metal can rapidly transfer heat energy out of your hand, making the metal feel particularly cold. Similarly, if the metal is hotter than your skin temperature, the metal can rapidly transfer heat energy into your hand, making the metal feel particularly hot.This is why concrete will feel especially cold to our bare feet in winter (the concrete transfers heat out of our feet rapidly), and especially hot to our bare feet in summer (the concrete transfers heat into our feet rapidly). Therefore, answer is a.

4. Ductility of a metal is described quantitatively by the overall change in length of a test rod which has been subjected to a constant load. Therefore, answer is b.

8. (a) True

(b) True