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考前速通

Quick Checklist​

(c)(i) Plotting — 2 分​

  • Scales chosen: 1, 2 or 5 per 2 cm square, graph > half grid
  • All points plotted accurately within half a small square
  • Error bars symmetrical on every point, length = 2×ΔY2 \times \Delta Y
  • Axes labelled with quantity and unit

(c)(ii) Lines — 2 分​

  • Best fit: straight line, equal points above and below
  • WAL: steepest OR shallowest through ALL error bars
  • Lines clearly labelled or distinguished

(c)(iii) Gradient — 2 分​

  • Two points on best fit line (not data points), spaced > half line length
  • gradient=Δy/Δx\text{gradient} = \Delta y / \Delta x with correct unit
  • WAL gradient calculated same way
  • uncertainty=∣best−worst∣\text{uncertainty} = |\text{best} - \text{worst}| expressed as ±\pm

(c)(iv) y-intercept — 1–2 分​

  • c=y−mxc = y - mx using a point on best fit line
  • NOT read from graph scale directly
  • Uncertainty from WAL if required
  • Correct unit given

Red Flags​

信号可能的问题
数据点分布明显弯曲检查 linearization 是否正确
Error bars 长短不一检查 ΔY\Delta Y 是否对称
所有点偏在线的一侧Balance 重新画 best fit
WAL 只需微小旋转检查是否真的是 steepest/shallowest
梯度值特别大/小检查坐标轴单位和计算
y-intercept 从图直接读除非原点在图上，否则必须计算

Key Formulas​

表达式含义
m=y2−y1x2−x1m = \frac{y_2 - y_1}{x_2 - x_1}gradient of straight line
c=y−mxc = y - mxy-intercept
Δm=∣mbest−mWAL∣\Delta m = \lvert m_{\text{best}} - m_{\text{WAL}}\rvertuncertainty in gradient
Δc=∣cbest−cWAL∣\Delta c = \lvert c_{\text{best}} - c_{\text{WAL}}\rvertuncertainty in y-intercept
提示

作图时按照 Point → Error Bar → Best Fit → WAL 顺序操作。最后做计算。不要先画线再画 error bar。