Beatty PURE PHYSICS PRACTICAL NOTES 6 Oct 2023

Beatty Secondary School O level Physics (6091) Science Department 1 PURE PHYSICS PRACTICAL NOTES 1. Reading and recording of raw data Precision of instruments The table below summarizes the precision of each instrument used in experiments. No Apparatus Smallest division Correct precision Example of recording Remarks 1 Ammeter (0 – 1 A) 0.02 A 0.01 A 0.24 A 0.31 A These instruments’ readings are recorded to half the smallest division. 2 Ammeter (0 – 1 A) 0.02 A 0.01 A 0.25 A 0.20 A 3 Voltmeter (0 – 3 V) 0.1 V 0.05 V 0.65 V 1.30 V 4 Voltmeter (0 – 5 V) 0.1 V 0.05 V 2.15 V 2.20 V 5 Laboratory thermometer (-10 to 110 ºC) 1 ºC 0.5 ºC 37.5 ºC 91.0 ºC 6 Half – metre rule 0.1 cm 0.1 cm 12.0 cm 12.1 cm These instruments’ readings are recorded to the smallest division. 7 Metre rule 0.1 cm 0.1 cm 88.3 cm 8 Protractor 1 º 1 º 36 º 45 º 9 Measuring cylinder (100 ml) 1 ml 1 ml or cm3 75 ml or cm3 10 Spring balance (0 – 1 N) 0.01 N 0.01 N 0.76 N 0.70 N 11 Spring balance (0 – 10 N) 0.1 N 0.1 N 3.7 N 3.6 N 12 Stop watch (digital) 0.01 s 0.01 s 36.54 s 20.72 s Reading to 2 d p unless otherwise stated. 13 Digital Micrometer screw gauge 0.01 mm 0.01 mm 2.00 mm 2.11 mm 14 Digital calipers 0.01 cm 0.01 cm 7.22 cm 7.89 cm 15 Electronic mass balance 0.01 g 0.01 g 121.00 g 2.45 g

Beatty Secondary School O level Physics (6091) Science Department 2 The method to obtain readings in some of the common instruments is discussed below. 1. Metre rule 2. Stop watch • Read to 2 d.p. unless otherwise stated (The time interval can be very short for some experiments and thus the question will specify to record timings to nearest second). • Record as 35.39 s • Read to 2 d.p. • Record as 1 min 35.39 s which is equivalent to 60 + 35.39 s = 95.39 s 3. Electronic mass balance • Reset the machine first (Press the “tare” button). • Once reading is stable, record reading accordingly in grams. 4. Vernier calipers • 2 d.p. (in cm) or 1 d.p (in mm) Note: Do not record timing as “3539” or “35 39” • Read to the smallest division. • Take note of the decimal place (d.p.) cm 1 d.p. (1.9 cm) mm whole number (19 mm) m 3 d.p. (0.019 m) 01: 35: 39

Beatty Secondary School O level Physics (6091) Science Department 3 5. Micrometer • 2 d.p. (in mm) 6. Thermometers (Laboratory) 7. Voltmeters & ammeters • Read up to half the smallest division for both. 2 d.p. Last digit: 0 or 5 2 d.p. Last digit: 0 to 9. • Read to half the smallest division. i.e. the last digit: 0 ºC or 5 ºC • Record the above as 31.5 ºC

Beatty Secondary School O level Physics (6091) Science Department 4 General precautions for experiments The tables below describe precautions that are taken in the various type of experiments. These precautions should be followed and will help improve the accuracy of the readings obtained. Mechanics Precautions Measurements of width, diameter, angles. etc • The eye must be placed vertically above the scale when reading the ruler/protractor/etc. to avoid parrallax error. • Take reading over a few points and find the average value. Period of oscillation • Make sure that pendulum is swinging in a plane so that correct timing of oscillation can be taken. • Allow a few oscillations to take place before starting the stopwatch. • Take the lowest point of oscillation as the reference point to start timing. • Fans must be switched off so that the time taken is not affected by draught. • Take 2 sets of readings per interval for 20 oscillations, find the average and divide by 20. Volume of irregular solid • Make sure there are no air bubbles in the liquid when taking readings. • Make sure solid is dry before lowering into liquid. • Ensure no liquid spillage or splashes when lowering the solid. Determining C.G of plane lamina • Ensure plumb line (a string with a bob), is hanged freely with the plane lamina at three locations. • After obtaining the intersection from two traced lines, use the third traced line to confirm the C.G. Principle of moments • Always measure the distance from pivot to centre of gravity of mass of object to obtain the perpendicular distance. Heat Precautions • The eye must be placed in line with the top of the meniscus of the mercury thread in the thermometer to avoid parallax error. • Switch off the fan so as to minimise heat loss to surrounding. • Stir the liquid in the beaker/boiling tube/test tube quickly to ensure even distribution of heat. • If lagging (insulation) is used, make sure it is adequte to reduce heat loss to surrounding. • If transferring a hot liquid from one container to another is required, transfer the liquid quickly so as to minimise heat loss to surrounding.

Beatty Secondary School O level Physics (6091) Science Department 5 Light Precautions Experiments involving pins • Pins must be placed vertically so that image can be located accurately. • The eye must be placed vertically above the scale when reading the ruler/protractor/etc. to avoid parallax error. • Make sure pins are reasonably far apart (at least 5 cm apart). • Close one eye when aligning pins and do not tilt head when looking at pins. • Check back using the refractive index of glass. (n of glass usually about 1.5; although could range from 1.48 to 1.96) Experiments involving lenses • The eye must be placed vertically above the scale when reading the ruler to avoid parallax error. • The illuminated object, lens and screen must be placed in line so that image can be obtained accurately. • In order to obtain a sharp image, the lens must be placed upright and parallel to the screen. The distance between lens and screen is the approximated focal length. • The torch light must be switched off when not in use so as to conserve the e.m.f of the batteries. Electricity Precautions • The eye must be placed vertically above the scale when reading the ruler/ammeter/voltmeter etc. to avoid parallax error. • All connections must be tightened so as not to increase the resistance in the circuit and readings taken. • Ensure positive terminal of meter is connected to positive terminal of batteries. • The zero error in meters must be corrected so as to avoid errors in meter readings. • Make sure that there in no ‘kink’ in the bare resistance wires (usually in potentiometer) as this would reduce the accuracy in the measurement of the length of wire. • The circuit must be switched off when not in use so that heat is not produced in the resistance wire (resistance of wire may vary because of difference in temperature) and also to conserve the e.m.f of the batteries. • When using the jockey, do not press it tightly on the wire as this will alter the thickness of the wire and hence changes its resistance. • The jockey must be held vertically on the wire so that point of contact with wire is small and reading taken will be accurate.

Beatty Secondary School O level Physics (6091) Science Department