Practicals

• Tips for answering practical questions

  • Identify the independent variable (the thing you change)
  • Identify the dependent variable (the thing you measure)
  • Identify the control variables (things you keep the same)
  • State the equipment used for each measurement
  • State the obvious (e.g. use a ruler to measure length)
  • Discuss the accuracy of measurements and how to reduce errors
  • Perform multiple/repeat measurements to calculate a mean
  • Write answers in bullet point format
• Spring constant

  The force required to stretch a spring by 1 unit of length
• Measuring spring constant

  1. Fix one end of spring next to a ruler and hang increasing masses from other end

  More accurate measurement - spring close to ruler as possible & get on eye level (parallax error)

  2. Measure extension of spring

  3. Plot force against extension and find gradient, which is the spring constant
• Newton's Second Law

  Force = mass x acceleration
• Verifying Newton's Second Law

  1. Attach masses to trolley on a track so they hang over a pulley and let them fall, measuring velocity by letting it pass through a photogate connected to a data logger

  2. Change the force by adding/removing masses, keeping total mass constant

  3. Plot force against acceleration and find the gradient, which is the mass
• Waves

  • Can use ripple tank and light to project waves onto a screen
  • Measure wavelength by taking a photo or by measuring 5 waves and dividing by 5
  • Measure frequency by counting how many waves pass a pencil line in 20 seconds and dividing by 20
  • Control - depth of water
• Measuring refractive index

  1. Place glass/plastic block on paper, shine light at an angle

  2. Draw outline of block and measure angles of incidence and refraction

  3. Calculate refractive index using sin(i)/sin(r)
• Infrared emission

  1. Fill a Leslie cube with hot water
  2. Use an IR detector to measure relative emission from diff surfaces
  3. Use a ruler to ensure distance is same each time
  4. Matte black best, silver worst
  5. Plot bar chart
• Infrared absorption

  1. Put thermometer and bung in test tubes with different materials wrapped around, same distance from a lamp
  2. Plot a bar chart
  3. Matte black is the best absorber and emitter, shiny the worst at both
• Refraction diagram


  trace it all on the paper

  
• glass block

  place a glass block on a piece of paper

  draw around the glass block and then remove from the paper draw a line at 90° to one side of the block (the normal)

  use a protractor to measure and then draw a line at an angle of 20°

  to the normal

  replace the glass block

  using a ray box and slit point the ray of light down the drawn line

  mark the ray of light emerging from the block

  remove the block and draw in the refracted ray

  measure the angle of refraction with a protractor

  repeat the procedure for a range of values of the angle of incidence