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COMMENTS FOR PR 4 FOCUSING ON PRACTICAL SKILLS

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RECORD OF MEASUREMENTS & CALCULATIONS I/AV/VV/I / Ω 0.150.352.3 (2 s.f.) 0.591.302.2 (2 s.f.)(3 s.f.)(2 s.f.) 1.002.20 (3 s.f.) UNIT!! Take note of s.f.!!

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PLOTTING GRAPH 1.Choose a scale: Use common, easy-to-read scales. For every 2 cm, start with 0.1, 0.2, 0.3, etc. If too small, increase to 0.05, 0.10, 0.15, 0.20, etc. If too big, decrease to 0.2, 0.4, 0.6. Make sure your scale can be easily read! Once you picked the appropriate scale, you should also decide whether you can include the origin. If possible, do try to include the origin. 2.Plot your points! 3.Draw a best fit line! Do not force your line to go through the first and last points, or the origin! It should reflect the trend of your points! 4.Label your axes with the symbol of the physical quantity and its appropriate unit.

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CALCULATING GRADIENT 1.Do not use your data points to calculate gradient, even if they lie on the best fit line. 2.Do not make the coordinates of your gradient triangle with a cross. Crosses are meant for data points only. 3.Choose points which lie nicely on the intersection of gridlines! 4.Use a fine pencil to draw your graph.

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WRITING THE CONCLUSION (COMMENTING ON RELATIONSHIP BETWEEN VARIABLES) Graph is a straight line Graph has a positive gradient Graph has a negative gradient Graph passes through origin (up to 2 small squares away) Graph does not pass through origin (or cannot tell) _____ decreases linearly as _____ increases _____ increases linearly as _____ increases _________ is directly proportional to ________

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QUESTIONS 1 When the rheostat is set to the maximum resistance, the current flowing through the circuit will be the minimum. This is to prevent a large current from flowing through the circuit, which can cause damage to the apparatus. This is a safety precaution. IT is not just to make the procedures more smooth by starting from the minimum and increasing gradually.

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QUESTIONS 2 This is to prevent the resistor from heating up and thus, affecting its resistance. Note that the resistors are not going to heat up until it can cause a fire! We are not dealing with such high voltage. Electric shock is also quite minimal. What does “accumulation of volts” mean?! There is also no “sudden spike” in the reading of the voltmeter…. Note that preserving the electromotive force is not significant for the short duration of the practical…

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QUESTIONS 3 When the connections are poor, readings on the ammeter and voltmeter will tend to fluctuate, making it difficult to obtain an accurate reading. OR When the connection are poor, cross sectional area in contact at the points of connection decreases. This will cause resistance in the circuit to increase, resulting in a decrease in current flow. Note that “poor contact” does not mean “no contact”

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QUESTIONS 4 Your answer from the gradient calculation with the appropriate unit. 5 The resistance of resistor R. In this experiment, you took the potential difference across the resistor R, therefore, you cannot be looking at resistance of the “whole circuit”

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RESISTANCE – OHM’S LAW Lesson 5. Resistance The amount of current flow in a circuit, and the amount of energy transferred to any useful device, depends.

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