Stress, strain and Young's modulus: Class 11 practice
Stress = force ÷ area, strain = extension ÷ original length (no unit). Read the method, follow the three worked examples, then try the six questions.
What you should know first
- Scientific notation
- Area of a circle
The idea behind stress, strain and young's modulus
Stress = force ÷ area, strain = extension ÷ original length (no unit). Young's modulus Y = stress ÷ strain = FL/(AΔL).
Step-by-step method
- Convert area to m² and lengths to m.
- Stress = F/A; strain = ΔL/L.
- Y = stress/strain, or rearrange for ΔL.
Worked example 1 (Basic)
A 300 N load hangs on a wire of area 1 mm². Find the stress.
- Stress = 300/1e-6
- = 3.00e+8 N/m²
- Answer: 3.00e+8 N/m²
Worked example 2 (Standard)
A 3 m wire of area 3 mm² (Y = 7.0e+10 N/m²) carries 700 N. Find its extension.
- ΔL = FL/(AY)
- = 10.000 mm
- Answer: 10.000 mm
Worked example 3 (Challenge)
A 5 m wire of area 5 mm² (Y = 1.2e+11 N/m²) carries 400 N. Find its extension.
- ΔL = FL/(AY)
- = 3.333 mm
- Answer: 3.333 mm
Common mistakes and misconceptions
- Leaving area in mm²
- Giving strain a unit
Practice questions
- (Basic) A 1900 N load hangs on a wire of area 5 mm². Find the stress.
- (Basic) A 1200 N load hangs on a wire of area 1 mm². Find the stress.
- (Standard) A 1 m wire of area 1 mm² (Y = 1.2e+11 N/m²) carries 1900 N. Find its extension.
- (Standard) A 3 m wire of area 4 mm² (Y = 2.0e+11 N/m²) carries 500 N. Find its extension.
- (Challenge) A 3 m wire of area 4 mm² (Y = 7.0e+10 N/m²) carries 1300 N. Find its extension.
- (Challenge) A 1 m wire of area 5 mm² (Y = 1.2e+11 N/m²) carries 1200 N. Find its extension.
Answer key with full working
- Q1: Stress = 1900/5e-6 → = 3.80e+8 N/m² → Answer: 3.80e+8 N/m²
- Q2: Stress = 1200/1e-6 → = 1.20e+9 N/m² → Answer: 1.20e+9 N/m²
- Q3: ΔL = FL/(AY) → = 15.833 mm → Answer: 15.833 mm
- Q4: ΔL = FL/(AY) → = 1.875 mm → Answer: 1.875 mm
- Q5: ΔL = FL/(AY) → = 13.929 mm → Answer: 13.929 mm
- Q6: ΔL = FL/(AY) → = 2.000 mm → Answer: 2.000 mm
Syllabus note
This skill is listed under "Mechanical Properties of Solids" for Class 11 in the NCERT/CBSE books. ICSE, IGCSE, IB and state boards may teach it in a different chapter or year.
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.
Related practice and notes
Frequently asked questions
Which chapter is stress, strain and young's modulus in?
"Mechanical Properties of Solids", Class 11 Physics (NCERT/CBSE). Other boards may place it differently.
How were the answers checked?
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.