Young's modulus of a metallic wire — practice questions

Question 1 · difficulty L1 · recall

Young's modulus is defined as

• A. strain divided by stress
• B. force divided by length only
• C. longitudinal stress divided by longitudinal strain within the elastic limit
• D. extension divided by area

Question 2 · difficulty L1 · understanding

The SI unit of Young's modulus is

• A. metre
• B. newton only
• C. joule per second
• D. pascal

Question 3 · difficulty L2 · understanding

For a wire of length L, area A and extension ΔL under force F, Young's modulus is

• A. FL/(AΔL)
• B. FΔL/(AL)
• C. AFL/ΔL
• D. F/(LΔL)

Question 4 · difficulty L2 · application

If the same force is applied to two wires of the same material and length, the thicker wire extends

• A. more
• B. less
• C. the same amount
• D. an amount independent of area

Question 5 · difficulty L3 · application

If wire length doubles with force, area and material unchanged, extension

• A. halves
• B. quadruples
• C. doubles
• D. stays unchanged

Question 6 · difficulty L3 · application

A wire has radius r. If radius doubles at fixed F, L and Y, extension becomes

• A. one-half
• B. twice
• C. four times
• D. one-fourth

Question 7 · difficulty L4 · analysis

Why should loads be added gradually in a Young's modulus experiment?

• A. To avoid shocks and help keep deformation within the elastic limit
• B. To change the material's Young's modulus deliberately
• C. To make wire area increase without bound
• D. To eliminate gravity

Question 8 · difficulty L4 · analysis

A load-extension graph is linear through the origin over a range. The wire in that range is obeying

• A. radioactive decay
• B. Hooke's law
• C. Snell's law
• D. Kirchhoff's loop law only

Question 9 · difficulty L5 · analysis

If diameter measurement has a small percentage error, why can it strongly affect calculated Y?

• A. Y depends only on diameter linearly
• B. diameter never enters the formula
• C. Area depends on diameter squared
• D. length is the square of diameter

Question 10 · difficulty L5 · analysis

A wire of length 2 m and area 1×10^-6 m² extends 1 mm under 100 N. Young's modulus is

• A. 2×10^8 Pa
• B. 5×10^10 Pa
• C. 1×10^14 Pa
• D. 2×10^11 Pa