VIEWS: 37 PAGES: 12 CATEGORY: Academic Papers POSTED ON: 5/24/2010
LESSON 4 - SCIENTIFIC Hypothesis INVESTIGATIONS A general statement about the relationship between a manipulated variable and a When physicists observe a particular physical responding variable. phenomenon they will as questions as to how or why it happens . A hypothesis will be put The hypothesis should be written as : forth and experiments or scientific The greater the………, the greater the……. investigations will be carried out to prove or Or disprove the hypothesis. If the experiments The bigger the…………., the smaller the….. bear out the hypothesis, the hypothesis may come to regarded as theory or law of nature. If Manipulated variable the don’t the hypothesis will be rejected or modified. The quantity whose values we deliberately choose In any experiment , the report on the to change or a primary variable which causes other experiment will be based on these guidelines secondary variable to change. and follows a sequence as shown in the following flow chart: Responding variable The quantity whose value depend on the manipulated variable or a secondry variable which changes in response to the change in the manipulated variable. Fixed variable The quantity whose value is kept constant throughout the experiment. Aim A statement to show the investigation of the variables involve. The aim of the experiment should be written as: To investigate the relationship between ………..and ……………… Apparatus Inference List the apparatus and materials used so that at Early assessment that is carried out to answer least a set of data for manipulated and responding the questions raised. variables can be determined. The inference should be written as : State the arrangement of the apparatus that can …………………depend on……………………. function by drawing a labeling diagram . Or The ……………..changes as the Procedure …………...changes State the method of controlling the manipulated variables State the method of measuring the responding variables Repeat the experiments at least four times. 20 Tabulating the data If the data too small or too big use the standard form number. Record the data in the following table For example Manipulated variable Responding variable Temperature /oC 10 20 30 40 50 Density, / kgm-3 9.7 8.5 7.3 6.6 5.1 x 104 How to plot the graph ? The title of the graph must be shown. The axes of the graph must be labelled with the Analysing the data unit used. For example: Plot a graph of ( Responding variable) against (Manupulated variable) How to tabulate the data ? The table muast be neatly drawn and the data arranged in either and rows. The names and symbols of the manipulated and The scale choosen must be easy to use. responding variables must be written together with Scales such 1:1 , 1:2 , 1:5 ,1:10 ,1:100 are the units. preffered in plotting a graph. For example, Odd scales such as 1:3 , 1:4 , 1: 6 , 1:7 , 1: 30 should be avoided in plotting a graph. Velocity,v / s Time , t / s Make sure the area covered by the plotted points must not be less than 50% of the area of the graph Volume , V / m3 Pressure , P / Pa paper. For example: The data shown in the table must be consistent in the number of decimal places in accordance with the respective measuring instruments. The scale on the axes must be uniform and clearly For example, marked with value. Length, l / cm Time , t /s For example: 0 12.8 2 25.6 4 39.4 6 52.2 8 75.0 21 All the points are marked with a symbol such as a y is directly proportional to x. cross or circle and the centre of the cross must or y x accurately positioned. or y = kx k = constant or y = mx m = gradient or y1 = y2 The best straight line or the best curve graph must x1 x2 be drawn. The best straight line or the best curve graph is the line that passes through most of the points plotted such that it is balanced by the number of points above and below the line.The line also must be smooth. y increases linearly with x or y = mx + c m = gradient c = intercept on axis-y y decreases linearly with x or y = -mx + c It is not advisable to plot graph by joining point to m = gradient point because the graph obtained is not smooth. c = intercept on axis-y y is inversely proportional to x atau y 1 x atau y = k x k = constant atau y1 x1 = y2 x2 How to analyse the data ? (a) Determine the relationship between two variables. Example : 22 (b) Determine the gradient of the graph Example Draw a suffiecienly large triangle to calculate the gradient of the graph. State value of the gradient with correct unit. The gradient of the graph is m = y2 - y1 x2 - x1 = QR QR (c) Determine the certain values from the graph. Certain important values can be obtained from the graph plotted by drawing a horizontal line or by extrapolating the graph. (d) State the precautions should be taken For example: The circuit connentions must be taken Off the switch when taking the raeding of the meters. Make sure the amplitude of oscillation is small. 23 TUTORIAL 4 4 Which of the following graphs show that y increases linearly with x? 1 Which of the following is the best way to tabulate the data ? A Voltage,V 0 5 10 15 20 Current,I 0 1.7 2.5 3.4 4.2 B Time,t /s 2 4 6 8 10 Density, / 2000 5000 8000 11000 14000 kgm-3 5 Hooke’s law states that applied force F is directly proportional to the extension x of C Period,T 10.5 15.3 19.8 27.9 36.0 spring if its elastic limit is not exceeded. Which /s of the following graphs shows the Hooke’s Distance,d 2.5 3.3 4.6 5.8 6.9 Law? /m D Object 5.1 8.7 11.6 16.5 18.6 distance ,u / cm Image 2.3 5 6.9 9 11.6 distance, v / cm 2 Which of the following scales is the most suitable to plot a graph? 6 The acceleration,a of an object is inversely proportional to the mass,m of the object A 1 cm : 3 unit B 1 cm : 5 unit under constant force. C 1 cm : 6 unit D 1 cm : 8.8 unit Which of the following graphs describes the relationship between a and m . 3 Which of the following is the best graph ? 24 7 An experiment is carried out to find the 12 The resistance R and temperature T for an relationship between mass and acceleration of electric conductor is given as R = r + aT with a trolley on a wooden runway. r as the resistance at 0oC dan a as a The experiment is repeated by adding the constant. number of trolleys. A graph of R against T is shown . The responding variable in this experiment is A the length of the wooden runway. B acceleration C mass What is the resistance ,R of the conductor at a 8 In a simple pendulum experiment, the length temperature 60oC ? of the pendulum and time for 20 oscillations are recorded. A 35 B 47 The length of the pendulum is a C 86 D 93 E 180 A manipulated variable B responding variable 15 The pressure ,P of the gas is directly C fixed variable proportional to the absolute temperature, T of the gas. When P = 100 ,T = 50. What is the value of P when T = 400. A 0.8A B 125 C 200 D 800 9 Based on the graph above, what is the E 2000 gradient of the graph? 16 A student carries out an experiment to find A - 1.5 B - 0.7 out the relationship between the change in C 0.7 D 1.0 length , y , of a spring and mass, m , of the E 1.5 load on the spring. The arrangement of the apparatus for the experiment is shown in Figure 1 . The length of the spring when a load is placed on the piston is l . 10 What is the unit of the gradient of the graph above? A m B m2 s C ms2 D ms- 2 11 A student plot a graph for a physical quantity , Q on axis-y against a physical quantity ,R on axis –x The relationship between Q and R is given by as Q - aR = b , where a and b are constants. The gradient of vthe graph is A a B R b Q C b D a 25 At the beginning of the experiment there is no Figure 6 and Figure 7. load. The length of the spring is lo . The actual length of lo is shown in Figure 2. The experiment is repeated by using load with mass , m , equal to 0.5 kg , 1.0 kg , 1.5 kg , 2.0 kg and 2.5 kg. The actual lengths of the spring when the different masses are used are shown in Figure 3, Figure 4 , Figure 5 , 26 27 (a) Based on the aim and the procedure of the experiment state the: (i) manipulated variable ________________________________ (ii) responding variable _________________________________ (iii) constant variable ________________________________ (c) On the graph paper , plot a graph of y against m. (b) Measure the length of the spring in Figure 2. (d) Based on your graph, state the lo = ___________________ relationship between y and m . Measure the lengths l of the spring in _________________________________ Figure 3 , Figure 4 , Figure 5 , Figure 6 and Figure 7 when different load are _________________________________ used. In each case, calculate the change in length, y , of the spring where; y = ( lo – l ) Tabulate your results for m ,l and y in the space below. 28 29 Graph T2 against l T2 / s2 5 4 3 2 1 l / cm 0 20 40 60 80 100 30 17 A student carries out an experiment to investigate the relationship between the length of a simple oscillating pendulum ,l , with its period, T. The experiment is repeated using different lengths,l, and their corresponding periods, T, are recorded. A graph of T2 against l , is then plotted as shown above. (a) Based on the graph, (i) State the relationship between T2 with l. ………………………………………….. ………………………………………….. (ii) Calculate period,T, when the length l = 45 cm. (Show your working) 18 The graph above represents graph W against V , where W and V are the distances on a wooden rod. (a) Based on the graph state the: (i) manipulated variable ________________________________ (iii) Calculate the gradient of the graph. (ii) responding variable _________________________________ (b) Calculate the gradient of the graph. (b) Using the value of the gradient obtained from (a)(iii) and the equation, l T 2 4 2 g calculate the acceleration due to gravity , g. (c) Determine the intercept on (i) axis- W .................................................... (ii) axis-V ..................................................... (c) State one precaution for this experiment. (d) State the equation of the line ……………………………………………… ............................................................... ……………………………………………… 31