Lecture Notes: Graph Plotting and Exam Marking

Overview

• Part of Video Series: Second part on question one in Paper Tree
• Focus: Plotting graphs and how they are marked by examiners
• Previous Video: Covered initial 10 marks allocation (tables, preliminary reading)

Key Points on Graph Plotting

Marks Allocation

• Three Marks for Graph Plotting:
  • Axis plotting
  • Quality of the graph

Mark Scheme Consistency

• Consistent across different graphs
• Focus on correct axis, plotting, and quality of the graph

Graph Axis and Scale

Sensible Scales

• One Two Five Rule:
  • Increments of 1, 2, or 5 (e.g., 1, 2, 3,... or 10, 20, 30,...)
• Avoid:
  • Fractions or unusual scales
  • Mid-point plotting without certainty

Graph Size and Labeling

• Occupy at least half the graph area
• Label axes with quantity and units
• Scale Marking:
  • Every 2 cm preferred, up to 4 cm acceptable

Plotting Points

Expectations

• Plot all observations from the table
• Point Size:
  • Diameter should be less than or equal to half a small square

Accuracy

• Plot at corners only
• Round to nearest whole number if unsure of mid-point accuracy

Quality and Line of Best Fit

Plot Quality

• At least five points plotted correctly out of six
• Trend:
  • Points within ±1 cm from line (varies yearly)

Best Fit Line

• Balanced Line:
  • Equal points above and below
• Anomalous Points:
  • Clearly indicate with a label
  • At least five points must remain after excluding anomalous points

Additional Graph Guidelines

Line Drawing

• Confidence in drawing lines: Use transparent rulers to help
• Do not adjust line mid-drawing

Gradient and Calculation

• Triangle for Gradient Calculation Required
  • Use large triangles
  • Hypotenuse should be greater than half the length of the line
  • Mark x and y coordinates on the triangle ends
• Display Calculation Method:
  • Include formula and substitution
  • Ensure sign of gradient matches the graph

Y-Intercept Considerations

• Only read directly from graph if it passes through the origin
• If not, use y = mx + c for calculation

Common Mistakes

• Missing labels on axes
• Incorrect scales and marks
• Plotting errors like oversized points
• Inadequate or absent gradient triangles
• Lack of clear working for calculations

Conclusion

• Importance of meticulous graph drawing
  • Pay attention to detail to avoid losing marks
• Anticipate further discussion on analyzing y-intercept and gradient in Part 3 of the series