RP: Investigating EMF and Internal Resistance

Cards (19)

  • What is the overall aim of the experiment?
    Investigate the relationship between e.m.f and internal resistance
  • What is the independent variable in the experiment?
    Resistance, R (Ω)
  • What are the dependent variables in the experiment?
    Voltage, V (V) & current, I (A)
  • What are the control variables in the experiment?
    E.m.f of the cell and internal resistance of the cell
  • What is the resolution of the voltmeter used?
    1 mV
  • What is the resolution of the ammeter used?
    0.1 mA
  • What is the method for measuring voltage and current in the experiment?
    1. Connect the cell and resistor in series.
    2. Record the voltmeter reading with the switch open.
    3. Set the variable resistor to maximum, close the switch, and record V and I.
    4. Vary the resistance and record V and I for at least 8-10 readings.
  • What is the equation relating e.m.f and internal resistance?
    E = I (R + r)
  • How can the equation for e.m.f be simplified?
    E = IR + Ir = V + Ir
  • What is the rearranged equation for voltage, V?
    V = –rI + E
  • How does the equation for voltage compare to the equation of a straight line?
    y = V, x = I, gradient = –r, y-intercept = E
  • What should you do to analyze the results of the experiment?
    1. Plot a graph of V against I.
    2. Draw a line of best fit.
    3. Measure the gradient and compare with manufacturer's value.
    4. Identify the y-intercept as e.m.f and gradient as negative internal resistance.
  • What are systematic errors in the experiment?
    Only close the switch briefly to avoid resistance changes
  • What are random errors in the experiment?
    Use fairly new cells and wait for readings to stabilize
  • What safety considerations should be taken during the experiment?
    • Switch off power supply if burning smell occurs.
    • Keep liquids away from electrical equipment.
    • Monitor electrical components for overheating.
  • What is the first step in determining e.m.f and internal resistance from a graph?
    Plot the data on a graph of V against I
  • How do you calculate the gradient from the graph?
    Gradient = ΔyΔx\frac{\Delta y}{\Delta x}
  • How is the internal resistance related to the gradient of the graph?
    Gradient = –r (Ω)
  • How is the e.m.f related to the y-intercept of the graph?
    Y-intercept = E (V)