NJC Physics practical exam revision notes

Important points for SH1 practical examination 1. Critical skills in measurement, recording measurements and calculations 1.1 Recording measurements instrument How are readings taken? smallest division / decimal place How should measurement be recorded? uncertainty due to resolution$ mass hanger and slotted mass value is engraved on instrument 1 g 1 g 1 g metre rule read graduated markings on the instrument 0.1 cm 0.1 cm 0.001 m 0.1 cm protractor 1o 1o 1o liquid-in-glass thermometers 1 oC 0.5 oC 0.5 oC measuring cylinder (100 cm3) 1 cm3 0.5 cm3 0.5 cm3 newton-meter (or spring balance) 0.4 N 0.2 N 0.2 N vernier callipers value shown on the digital display 0.01 mm value on digital display # last decimal place micrometer screw gauge 0.001 mm value on digital display # last decimal place stopwatch 0.01 s value on digital display @& last decimal place electronic mass balance 0.01 g value on digital display last decimal place $ This uncertainty is due to instrumental limit only. Refer to section 1.4 on estimating percentage uncertainty. # You may record values from vernier callipers to the nearest 0.1 mm and micrometer screw gauge to the nearest 0.01 mm. @ You may record the stopwatch timing to nearest 0.1 s. & When stopwatch is running continuously while you measure how other quantity changes with time, you may record the timings to nearest 1 s or 0.1 s. 1.2 Expressing calculated values to the correct number of significant figures How is the value calculated? How is the calculated value recorded? Example Multiplication and/or division and/or reciprocal and/or power of quantities The s.f. of the final value should follow the least s.f. of the quantities used in the calculation. Example 1 The two measured quantities are A = 10.2 and B = 2.3. The calculated quantity C is related to A and B by the formula C = AB2. C = (10.2)(2.3)2 = 53.958 = 54 B has the least s.f. among the values and so C is expressed as 2 s.f. Example 2 The measured quantity is x = 10.2 cm and C = 1x. C = 110.2 = 0.0980 cm–1 x is 3 s.f., so C is expressed as 3 s.f. Addition and/or subtraction of quantities The d.p. of the final value should follow the quantity with the least d.p. of the quantities used in the calculation. The two measured quantities are X = 10.2 and Y = 2.33. The calculated quantity Z is related to X and Y by the formula Z = X + Y. Z = 10.2 + 2.33 = 12.53 = 12.5 X has the least d.p. among the values and so Z is expressed to one d.p. Average of a set of repeated values The final value should be recorded to the same decimal place (d.p.) as the measured values. The two repeated timings are 20.23 s and 20.30 s. Average timing = 20.23!20.302 = 20.265 s = 20.27 s (same d.p. as the measurement) 1.3 Critical skills Vernier callipers and micrometer screw gauge • Zero the device by pressing the “zero” button (venier callipers) or the “reset” button. • Measurement should be repeated at different positions to account for non-uniformity. Calc