physics

Precision ● Ammeter — 0.01A ● Voltmeter — 0.05V ● Thermometer — 0.5C ● Metre ruler — 0.1cm or 0.001m ● Protractor — 1 deg ● Measuring cylinder — 0.5cm3 ● Spring balance —0.1N(for 0-10N), 0.01N(for 0.10N) ● Stopwatch — 0.1s ● Mass — 0.1g When asked to obtain average value, must draw out table of at least 3 different values and calculate average (follow dp) When asked to find period, find average of time taken for 20 oscillations, then divide by 20 again Graph - axis, scale, points, best fit, trend, range - Plot at least 5 readings for straight line and 8 readings for curve - Readings interpreted from graph should be read to half of the smallest square - MUST ALWAYS HAVE ORIGIN Table - Headings - Processed data follow sf of raw data - Dp of raw data follow instrument (must be same throughout the column) - Range must be more than 50% of instrument, eg metre ruler range must be more than 50cm Relationship between x and y - X is linearly related to y, with negative/positive gradient - Directly proportional - As x increases, b decreases at at a decreasing rate Precautions - [measurements] eye must be placed vertically above the scale when reading the ruler/protractor to avoid parallax error - [measurements] take reading over a few points and find average value - [pendulum] take 2 sets of readings per interval for 20 oscillations and find the average by dividing by 20 - [pendulum] the time for the first few swings should not be taken and only start timer when oscillations are steady

- [measuring volume of irregular solid] make sure solid is dry before lowering into liquid and ensure no liquid spillage or splashes when lowering the liquid - [circuits] circuit must be switched off when not in use so that heat is not produced in the resistance wire and also to conserve the emf of the batteries Source of error - [mechanics] the time taken for the oscillation is too short, causing inaccuracy in the timing due to human reaction time to be significant - [mechanics] difficulty to read the markings on the ruler as the strings with the loads are swaying - [mechanics] difficult to judge the exact position of where the metre rule is clamped - [mechanics] the difficulty to judge the position of the loop to be just above the ruler - [moments] the diameter of the pivot is large and errors will arise when drawing the lines to join the center to the pivot, making the centre of gravity located inaccurate - [moments] the string used to make the plumbline is too thick, when 2 points are marked on the lamina, its centre is difficult to locate to draw the line through - [moments] the card is light and keeps oscillating with the slightest movement of air, making it difficult to mark the 2 points on the card. This affects the accuracy of the line drawn and thus the centre of gravity located - [heat] there is heat loss to/gain from the surroundings hence leading to inaccurate values of - [light] the holes created by the pins are too large as the pin is too thick, this makes the centre of the pin hard to locate and makes drawing the line inaccurate and affect reading. Use a thinner pin such that the holes created are smaller so that locating the center of the holes to draw line through the center of the 2 relevant points are easier - [light] (for determining sharp image)there is a range of values of v in which the image of the object for a particular value of u, appears sharp. This will affect the accuracy of the v value and hence affect the accuracy of 1/v. Therefore, the focal length obtained from the graph will be inaccurate - [light] when the board is shifted, the mirror tends to be off aligned from the drawn line, this will cause the pins aligned to be off. Hence the line drawn through the hole will be inaccurate thereby affecting the value of - [light] Pins are placed at least 5 cm apart, to reduce uncertainty when aligning the pins, and determine a more accurate path travelled by the incident ray. This will give a more accurate r value - [light] Place my eyes level with the glass block and when performing alignment of the pins, to avoid parallax error and to obtain a more accurate r value - [circuits] as current increase when rheostat is adjusted, temperature of resistor might increase, causing resistance of resistor to change and thus affecting the value of the current and potential difference recorded - [circuits] when the circuit is closed for too long, the heating effect of the current on the resistance wire will increase, this will affect the total resistance of the circuit and hence affecting the readings on the ammeter and voltmeter

- [circuits] the point of contact between the wire and the jockey is not consistent due to different amounts of pressure applied. This will affect the ammeter reading as the ammeter needle keeps fluctuating when the pressure applied on the wire by the jockey varies - [circuits] the cross sectional area of the resistance wire may not be uniform, so the resistance of the wire involved may not be proportional to its length, this will affect the accuracy of the current obtained when L is varied - [circuits] there may be kinks on the resistance wire, this will affect the length of the wire recorded as the presence of kinks on the wire will cause the actual length to be longer than what is recorded - [circuits] the emf of the battery might have changed after first student has done the experiment - [circuits] both wires cannot be straightened, causing the value of r recorded to be inaccurate - [circuits] the clips at the ends of both wires may not be exactly at the edge of the tape, causing reading of r recorded to be inaccurate - Perception of motor turning slowly is subjective so might end up with different speed of rotation Within its limits of experimental error… Qns ● Explain why measuring the time for 20 oscillations, rather than 1 oscillation gives a more accurate value of T ○ It reduces human reaction time error as when there are more oscillations, the human reaction time error can be divided with a larger multiple, thus each oscillation will have reduced human reaction time error ● Describe one precaution that you have taken to ensure that the readings are accurate (for spring extension practical) ○ Ensure that when the spring balance is held vertically, the reading on the spring balance is 0.0.N ● How to determine thickness of the wire of the spring used (for spring extension practica