H2 Physics Practical Notes

phy prac notes docs ver. PHYSICS PRACTICAL NOTES General Notes : ● For readings , the absolute uncertainty is half of the smallest division of the apparatus ● For measurements , the uncertainty is the sum of 2 absolute uncertainties ● Record measurements to the same no. of d.p. as its uncertainty ● When unsure, just take ≥ 3 repeated readings and calculate the average ● For tables and graphs, need to write units for “cos( θ /°)” ● Percentage difference between 2 values = difference/average x 100% ● Only round off to least s.f./d.p. for final answer , leave intermediate workings in 5s.f. ● For trigo datasets, input sin(45°) as =SIN(RADIANS(45)) Number of Significant Numbers / Decimal Places : ● Electronic Balance (in grams) – 2d.p. ● Rulers (in centimetres) – 1d.p. ● Thermometer – 1d.p. (to the nearest 0.5ºC) ● Ammeter – 2d.p. (to the nearest 0.05A) ● Voltmeter – 2d.p. (to the nearest 0.01V) ● Protractor - 0d.p. (to the nearest 1°) ● Calculated Values – least s.f. of raw data ● Percentage Uncertainty – 2s.f. Uncertainties of Apparatus (for MEASUREMENTS ) : Apparatus On Stable Surface On Unstable Surface Digital Stopwatch 0.3 s Protractor 1° 3° Rule 0.1 cm 0.2 cm Depth Rod of Digital Caliper 0.2 mm

✏ When Sketching Graphs from Excel : ● Write “ Plot a graph of YYY against XXX. If a straight line is obtained, AAA is the gradient and BBB is the vertical-intercept ” at the top ● Ensure that the size of the graph is larger than ½ of the grid ● Replace “x” and “y” with the variables used in the experiment ● Include units for axes, gradients and vertical-intercepts if possible ● Leave the values for gradients and vertical-intercepts in the same number of s.f. as raw data in the table ● DON’T plot on Excel, but circle and label “anomalous data point” on sketch if any 💻 CSV Data Question : ● Importing CSV Data into Excel ○ Open Microsoft Excel ○ Click on File > Open > Browse and select your CSV file ○ If needed, use the Text to Columns tool under the Data tab ● Eliminating Unrequired Data ○ When creating a chart or performing calculations, select only the relevant range instead of the whole dataset OR copy only what you need ● How to select data quickly 1. Click on the first cell of your data (for example, A1) 2. Hold down Ctrl + Shift 3. Press one of the arrow keys ( → , ← , ↑ , ↓ ) 4. Ctrl + Shift + ↓ : selects all the data in the column below your starting cell until the next blank cell 5. Ctrl + Shift + → : selects all the data in the row to the right until the next blank cell OR (with mouse) click first cell, hold shift and left click last cell ● Finding Area Under a Graph Using the Trapezium Method ○ Ensure your x-values are in one column, and y-values are in the next ○ In the next column, enter the trapezium rule formula for each pair of points: ■ e.g. =0.5*(A3 - A2)*(B2 + B3) ( Assuming A2 and B2 are your first x and y values, and A3 and B3 are the next ) ○ Use “ =SUM(C2:C[n]) ” to calculate the total area under the graph

🧠 CAQs Q Calculate the percentage uncertainty in the frequency of the motion. A ● t represents the average time taken for N oscillations Q Do the results of your experiment support the relationship suggested? A ● Since the percentage difference in k values (XX%) is smaller / greater than (percentage uncertainty calculated earlier OR 10% ), the results of my experiment support / do not support the relationship Q Comment on any anomalous data or results that you may have obtained. Explain your answer. A ● Absence of anomalous data : ○ No points deviate significantly from the linear trend set by all the data points. All data points are evenly scattered about the best fit line. ● Presence of anomalous data : ○ (X, Y) is anomalous as it deviates significantly from the linear trend set by the other data points Q Discuss whether the linear relationship suggested is valid, based on the data. A ● Since the data points show a curvature and the r 2 value is far from 1 , the relationship suggested is invalid Q Justify the number of significant figures which you have given for x 2 A ● x 2 is calculated from the raw values of x so it follows the number of significant figures of x Q State and explain why it is important to stir the water during heating. A ● To ensure that the water has a uniform temperature and that the temperature measured is representative of the entire water sample, leading to more accurate results Q Why is it better to use a temperature sensor/data logger instead of a thermometer/stopwatch? A ● Using a thermometer and stopwatch is less effective as it leads to inaccurate readings. This is because they rely on human reaction time and judgement . OR

● The precision of a thermometer is lower than that of a temperature sensor and data logger. Hence, the calculated results will be less accurate. Q Would you expect the Power-Resistance graph to go through the point (0, 0)? Give your reasons. A ● Yes, if the component does not have resistance , then it will not emit any power Q Explain why using a potentiometer to determine the e.m.f. of a cell is preferable to using a voltmeter/DMM A ● A potentiometer is more accurate because it measures the e.m.f. at the null point, where no current is drawn from the cell so there is no potential drop across the cell's internal resistance , allowing it to measure actual e.m.f. ● In contrast, voltmeters draw a small current, causing a voltage drop (V = Ir) across the internal resistance (r) , so it measures a terminal p.d. that is < actual e.m.f. Q Explain why the absolute uncertainty in I decreases over time. A ● The absolute uncertainty in t remains the same as it is caused by human reaction time ● As the rate of change of I decreases, the absolute uncertainty in I also deceases Q Explain why you might not have enough results to reach a valid conclusion. A ● The number of springs is limited by the height of the retort stand