4E/5NA Practical Skills

Name : _________________________________ ( ) Class : _________ Date: _________ _________________________________ ____________________________________________________________ _______________________ Practical Skills Worksheet Page 1 St. Patrick’s School Secondary 4 Science (Physics) Topics : Practical Skill Worksheet Making Observations and Presenting Data 1. Raw Data Raw data are readings or measurements taken directly from a measuring instrument. This is expressed to a fixed number of decimal places dictated by the units and precision of the instrument. [Refer to table below] Apparatus Smallest Division Examples Half metre or metre rule 0.1 cm 8.4 cm, 12.1 cm Vernier caliper 0.01 cm 2.75 cm, 5.38 cm Micrometer screw gauge 0.01 mm 2.10 mm, 3.26 mm Electronic balance 0.1 g 121.0 g, 86.2 g 0.01 g 121.10 g, 86.21 g Stopwatch (digital) 0.01 s 28.69 s Thermometer (-10 0C to 110 0C) 1.0 0C 23.0 0C, 29.5 0 C Measuring cylinder (100 cm3) 1.0 cm3 18.0 cm3, 7.5 cm3 Spring balance (0 – 10 N) 0.1 N 3.7 N, 5.8 N Ammeter (0 -1 A) 0.02 A 0.20 A, 0.54 A Milliammeter (0 – 100 mA) 2 mA 20 mA, 35 mA Voltmeter (0 – 5V) 0.1 V 2.5 V, 3.6 V

_________________________________ ____________________________________________________________ _______________________ Practical Skills Worksheet Page 2 2. Tabulation Example of Table with raw and processed data: Independent Variable l /m Time for 20 oscillations tave / s T /s T2 / s2 t1 / s t2 / s Guidelines: (a) Correct symbols and appropriate units are used for headings eg. length l and its unit metres are written as l/m and not as l (m). (b) The first column of the raw data should be the independent variable. (c) There should be a minimum of 5 to 6 readings for a straight line and 8 readings for a curve. (d) The independ ent variables should be arranged in increasing order and at regular intervals. (e) Measurements of dependent variable are repeated (where possible) to obtain an average value. 3. Processed Data (i) Processed data are readings obtained from calculations (usually multiplication or division) of one or more sets of raw data. For example, in the experiment to determine the period of a simple pendulum, a metre rule and a stopwatch are used to measure the length and time t1 and t2 of n oscillations of the pendulum. The values obtained are called raw data. To determine the average time tave and the period T of the pendulum, the following mathematical operations are carried out: tave = (t1 + t2) and T = tave where n = number of oscillations 2 n The average time tave and period T are called processed data. Raw Data Processed Data Dependent Variables

_________________________________ ____________________________________________________________ _______________________ Practical Skills Worksheet Page 3 (ii) The general guidelines in the calculation of processed data are illustrated in the table below. Mathematical Operations Guideline Example Addition: A + B = C C will have the least number of decimal place (i.e. either A or B) (i) 10.25 + 2.4 = 12.7 (1 d.p.) (ii) 2.432 + 1.72 = 4.15 ( 2 d.p.) Subtraction: A – B = D D will have the least number of decimal place (either A or B) (i) 9.382 – 8.51 = 0.87 (2 d.p.) (ii) 120 – 18.3 = 102 (no d.p.) Average: A + B + C = D 3 D will have the same number of decimal plac es as A, B or C. D = 1.25 + 1.24 + 1.27 3 = 1.25 (2 d.p.) Multiplication: A x B = C C will have the least number of significant figures (either A or B). 16.42 x 0.211 = 3.46 (3 s.f.) Division: C = E D E will have the least number of significant figures (either C or D). 2.735 = 8.34 (3 s.f.) 0.328 Division: T = tave n T will have the significant figures of t ave. The significant figures in n are not taken into account as it is a whole number with no inherent error. T = tave = 22.0 = 1.38 16 16 (3 s.f.)

_________________________________ ____________________________________________________________ _______________________ Practical Skills Worksheet Page 4 Example of Table with raw and processed data: Independent Variable l /m Time for 20 oscillations tave / s T /s T2 / s2 t1 / s t2 / s Handling Experimental Observations and Data Characteristics of a Good Graph 1. Axes (a) Axes must be labeled with the correct physical quantity and unit . The quantity and unit must be the same as the heading of the table of results. (b) Values in decimal places must be written along the axes at regular intervals (eg. 1 cm or 2 cm apart). (c) Independent variable is plotted along the horizontal (x) axis while the dependent variable is plotted along the vertical (y) axis. 2. Scales (a) Choose a suitable scale in order to make full use of the graph paper. The span of the first to the last plotted points should be greater than half the page. Example : Figure 1.1 (unacceptable) and Figure 1.2 (acceptable) unacceptable Figure 1.1 acceptable Figure 1.2 Raw Data Processed Data Dependent Variables

_________________________________ ____________________________________________________________ _______________________ Practical Skills Worksheet Page 5 (b) If points lie outside the graph grid as shown in Figure 1.3, the scale is incorrect and has to be scaled down so that all points lie within the graph grid. 3. Plotting Points on the Graph Data points must be clearly and accurately marked. Use crosses (x) to plot the data points. 4. Drawing the Best Fit Line or Curve (a) Make sure that the number of points on each side of the line is about the same and that they are close to the line as possible. Example: Figure 1.6 (acceptable) and Figure 1.7 (unacceptable). Figure 1.3 Figure 1.6 Figure 1.7

_________________________________ ____________________________________________________________ _______________________ Practical Skills Worksheet Page 6 (b) If the graph is a curve, do not simply join one point to another point. Instead, draw a smooth curve through it. - Buy a curve ruler. Example: Figure 1.8 (unacceptable) and Figure 1.9 (acceptable) (c) The line or curve must be thin and very neat . Thick or kinked line or curve introduces errors in the calculations of gradients and intercepts. Figure 1.8 Figure 1.9 Unacceptable Acceptable

_________________________________ ____________________________________________________________ _______________________ Practical Skills Worksheet Page 7 Practice 1. Plot a graph of V (y-axis) against θ (x-axis) based on the values given in the table below. [4] V / cm3 θ / oC 7.0 7.0 7.2 14.0 7.6 20.0 8.2 37.0 8.8 45.0 9.6 55.0 10.5 64.0 12.2 70.0

_________________________________ ____________________________________________________________ _______________________ Practical Skills Worksheet Page 8 2. Plot a graph of I1 (y-axis) against I2 (x-axis) based on the values given in the table below. [4] I1 / A I2 / A 0.50 0.10 0.42 0.12 0.33 0.14 0.25 0.16 0.18 0.18