Materials

Question 1

Describe the forces required to shape a spring or wire.

Answer 1

A pair of equal and opposite forces are required, with tensile forces acting away from the center to stretch the spring (extension) and compressive forces acting towards the center to shorten it (compressive deformation).

Question 2

Define Hooke’s law.

Answer 2

Hooke’s law states that for a material within its elastic limit, the force applied is directly proportional to the extension of the material.

Question 3

How is Hooke’s law mathematically expressed?

Answer 3

Hooke’s law is expressed as F = kx, where F is the force applied, k is the force constant, and x is the extension.

Question 4

What happens when the elastic limit of a material is reached according to Hooke’s law?

Answer 4

Once the elastic limit is reached, Hooke’s law is no longer obeyed, and the material will not return to its original shape.

Question 5

Explain the significance of the force constant (k) in Hooke’s law.

Answer 5

The force constant (k) measures the stiffness of the material; a larger k indicates a stiffer material.

Question 6

What does the gradient of the force-extension graph represent for a spring?

Answer 6

The gradient of the line in the force-extension graph represents the force constant of the spring.

Question 7

Differentiate between elastic and plastic deformation in springs.

Answer 7

Elastic deformation occurs when a spring returns to its original shape after the force is removed, while plastic deformation results in permanent deformation where the spring does not return to its original length.

Question 8

What characterizes the force-extension graph of a metal wire?

Answer 8

A metal wire obeys Hooke’s law and shows elastic deformation until its elastic limit, after which it experiences plastic deformation.

Question 9

How does the unloading curve differ from the loading curve in the context of plastic deformation?

Answer 9

The unloading curve shows how plastic deformation leaves a permanent extension in the material, differing from the loading curve which is the same until the elastic limit.

Question 10

What is the relationship between tensile forces and extension in a spring?

Answer 10

Tensile forces act away from the center of the spring, causing it to stretch and resulting in extension.

Question 11

What occurs when compressive forces are applied to a spring?

Answer 11

Compressive forces act towards the center of the spring, leading to compressive deformation and shortening the spring.

Question 12

Describe the behavior of rubber under stress.

Answer 12

Rubber does not experience plastic deformation and does not obey Hooke’s law.

Question 13

What does the area between the loading and unloading curves in a hysteresis loop represent?

Answer 13

The area represents the energy required to stretch the material, which is converted to thermal energy when the force is removed.

Question 14

Define polyethene in terms of its mechanical properties.

Answer 14

Polyethene is a polymeric material that does not obey Hooke’s law and experiences plastic deformation when force is applied, making it easy to stretch into new shapes.

Question 15

How can force-extension characteristics be investigated?

Answer 15

By using a test setup with a clamp stand, meter ruler, and standard masses to measure the extension of materials like springs, rubber bands, and polythene strips.

Question 16

What is the purpose of a fiducial marker in the force-extension experiment?

Answer 16

The fiducial marker is used to mark the original length of the material being tested.

Question 17

How can errors be minimized during the force-extension experiment?

Answer 17

Errors can be minimized by reading extension values at eye-level and using a set square to ensure the ruler is straight.

Question 18

What is the method to determine the force constant of a material?

Answer 18

The force constant can be determined by drawing a graph of force against extension and finding the gradient of the straight section within the elastic limit.

Question 19

Explain how the spring constant changes when springs are used in series.

Answer 19

In series, the total spring constant (k) is calculated using the formula 1/k_total = 1/k1 + 1/k2 + 1/k3.

Question 20

Describe the calculation of the spring constant when springs are used in parallel.

Answer 20

In parallel, the total spring constant (k) is the sum of the individual spring constants: k_total = k1 + k2 + … + kn.

Question 21

Describe the process of elastic deformation in materials.

Answer 21

When a material is deformed elastically, work is done and transferred into the material, stored as elastic potential energy, which is released when the material returns to its original length.

Question 22

How is elastic potential energy calculated in a material?

Answer 22

Elastic potential energy can be calculated by finding the area under a force-extension graph, which is a triangle, using the formula E = ½ F x.

Question 23

What is tensile strain and how is it expressed?

Answer 23

Tensile strain is defined as the extension or compression of a material per unit of its original length, expressed as a ratio or sometimes as a percentage.

Question 24

Define tensile stress and its unit of measurement.

Answer 24

Tensile stress is defined as the force applied to a material per unit cross-sectional area, measured in Nm-2 or pascal (Pa).

Question 25

Explain the Young modulus and its significance.

Answer 25

The Young modulus is defined as the ratio of stress to strain, representing the material’s stiffness and is independent of the shape and size of the material.

Question 26

How can the Young modulus of a metal wire be determined?

Answer 26

The Young modulus can be determined by applying various forces to a wire, measuring its extension, and calculating stress and strain from the recorded values.

Question 27

What is the formula for calculating the Young modulus?

Answer 27

The formula for calculating the Young modulus is E = Stress / Strain = σ / ε.

Question 28

Describe the procedure for measuring the diameter of a wire to determine its Young modulus.

Answer 28

A micrometer is used to measure the diameter of the wire at several points, and an average is taken to reduce error, which is then used to find the cross-sectional area.

Question 29

What happens to the work done when plastic deformation occurs in a material?

Answer 29

When plastic deformation occurs, the work done is not stored as elastic potential energy but is used to rearrange the atoms into their new permanent positions.

Question 30

How is the area under a force-extension graph related to elastic potential energy?

Answer 30

The area under a force-extension graph represents the elastic potential energy stored in the material during elastic deformation.

Question 31

Describe the formula used to calculate force in relation to mass and acceleration.

Answer 31

The formula is F = ma, where F is force, m is mass, and a is acceleration.

Question 32

How is the Young modulus for a material determined from a stress-strain graph?

Answer 32

The Young modulus is determined by calculating the gradient of the stress-strain graph.

Question 33

Define ultimate tensile strength (UTS).

Answer 33

Ultimate tensile strength (UTS) is the maximum breaking stress that can be applied to a material before it fails.

Question 34

What happens at the limit of proportionality on a stress-strain graph?

Answer 34

At the limit of proportionality, Hooke’s law is obeyed, meaning stress is directly proportional to strain.

Question 35

Explain the significance of the elastic limit on a stress-strain graph.

Answer 35

The elastic limit is the point beyond which a material will experience plastic deformation and not return to its original shape.

Question 36

How do stress-strain graphs differ for brittle materials like glass compared to ductile materials?

Answer 36

Brittle materials show elastic behavior until they snap without plastic deformation, while ductile materials undergo elastic deformation followed by plastic deformation before breaking.

Question 37

What characterizes the loading and unloading curves of elastic materials like rubber?

Answer 37

In elastic materials like rubber, the unloading curve differs from the loading curve because some energy is lost as thermal energy during deformation.

Question 38

Describe the behavior of ductile materials under stress.

Answer 38

Ductile materials experience elastic deformation until their elastic limit, then undergo plastic deformation before reaching their ultimate tensile strength and breaking point.

Question 39

What is indicated by the yield points Y1 and Y2 on a stress-strain graph?

Answer 39

Yield points Y1 and Y2 indicate where there is rapid extension of the material, marking the transition from elastic to plastic deformation.

Question 40

How does the stress-strain behavior of a brittle material differ from that of an elastic material?

Answer 40

A brittle material shows no plastic deformation and snaps at the breakpoint, while an elastic material can endure significant stress without permanent deformation.