practical 4 - young's modulus

• equipment

  • 2x 1.5m long steel wires
  • main scale and vernier scale
  • 1kg masses and 2x 1kg holders
  • micrometer
  • metre ruler
• method

  • set up apparatus
  • measure initial length of test wire
  • measure diameter of test wire at various points using micrometer and record mean diameter
  • add 1kg mass holder to both wires so they are taut and record initial scale reading
  • add additional 1kg mass to test wire and record new reading
  • find extension by subtracting initial from new reading
  • add another 1kg and repeat adding 1kg until 8kg
  • repeat experiment twice more and find mean extension for each mass
• graphs and calculations

  • calculate cross-sectional area of wire
  • $A=$$\frac{\pi d^2}{4}$
  • find force on test wire for each mass
  • $F=$$mg$
  • plot graph of force against extension and draw line of best fit
  • young modulus = length x gradient / area
  • $E=$$\frac{stress}{strain}=$$\frac{\frac{F}{A}}{\frac{e}{l}}=$$\frac{Fl}{Ae}=$$\frac{lG}{A}$
  • G is the gradient
• safety

  • wire is stretched tightly and could break injuring someone
  • masses could fall and cause injuries

  precautions

  • wear safety goggles
  • pad a tray below the masses
• improvements

  • comparison wire compensates for sagging of the beam and thermal expansion effects and provides reference point to measure mean against
  • original length of test wire should be as long as possible to reduce uncertainty