practical skills

• Standing waves on a string

  1. Set up vibration generator and signal generator

  2. Thread string through and tie to retort stand

  3. Add masses to create tension

  4. Observe standing wave pattern

  5. Measure frequency and length
• Standing waves on a string

  • First harmonic has nodes at each end and an anti-node in the middle
  • Can vary length, tension, and mass per unit length to see effects on frequency
• Equation for speed of wave: v = 2fL
• Interference (Young's double slit and diffraction grating)

  1. Use class 2 laser (power < 1mW)

  2. Set up double slit apparatus and measure slit separation

  3. Measure distance to screen

  4. Measure fringe width

  5. Plot graph of fringe width vs distance

  6. Use gradient to calculate wavelength

  7. Set up diffraction grating apparatus

  8. Measure angles of diffraction maxima

  9. Plot graph of sin(theta) vs order

  10. Gradient gives wavelength
• Interference

  • Double slit: W = lambda*D/s

  Diffraction grating: nλ = d sin(θ)
• Finding the value of G by free fall method

  1. Use electromagnet to hold steel ball

  2. Release ball and measure time of fall between light gates

  3. Use s = 1/2 gt^2 to calculate g
• Finding G by free fall

  • Measure distance between light gates and time of fall
  • Use s = 1/2 gt^2 to calculate g
• Young's modulus

  1. Stretch wire and measure extension

  2. Calculate Young's modulus from stress-strain relationship
• Resistivity of a wire

  1. Use circuits to measure resistance of wire

  2. Calculate resistivity from resistance, length and cross-sectional area
• Internal resistance and EMF of a cell

  1. Use circuits to measure voltage with and without load

  2. Calculate internal resistance and EMF from voltage measurements
• Typical setup for measuring time of fall

  1. Place something between two light gates

  2. Use an electromagnet to hold a steel ball bearing in place

  3. Turn off electricity to demagnetize and let ball fall

  4. Connect to a timer to measure time of fall
• s

  Distance between light gates
• Alternative setup for measuring time of fall

  1. Use a timer connected to electromagnet to start timer

  2. Have a plate at bottom that stops timer when ball hits it
• The setup depends on the data logging equipment available
• Using the s=ut+1/2at^2 equation to find g

  1. Replace a with g

  2. Rearrange to 2s/t = gt + 2u

  3. Plot 2s/t vs t to get a straight line

  4. Gradient is g
• Gravitational field strength g should be around 9.81 m/s^2
• Young's modulus

  Ratio of stress to strain
• Measuring Young's modulus using a wire

  1. Clamp one end of wire firmly

  2. Attach other end to pulley and weights

  3. Measure change in length as weight increases

  4. Calculate stress, strain, and Young's modulus
• Stress

  Force per unit area
• Strain

  Change in length divided by original length
• Young's modulus for steel is around 210 GPa
• Measuring wire resistivity

  1. Set up circuit with power supply, ammeter, voltmeter, and wire sample

  2. Vary length of wire and measure current and potential difference

  3. Use V=IR and A=πr^2 to calculate resistivity
• Resistivity

  Material property measured in ohm-meters
• Measuring EMF and internal resistance of a cell

  1. Set up circuit with cell, voltmeter, ammeter, and variable resistor

  2. Vary external resistance and measure terminal voltage and current

  3. Plot V vs I to find gradient (-internal resistance) and y-intercept (EMF)
• EMF

  Electromotive force, voltage when no current flows
• Internal resistance

  Resistance within the cell