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1.5 Scientific Investigation

When physicists observe a particular physical phenomenon they will as questions as to how or why it happens . A hypothesis will be put forth and experiments or scientific investigations will be carried out to prove or disprove the hypothesis. If the experiments bear out the hypothesis, the hypothesis may come to regarded as theory or law of nature. If the don’t the hypothesis will be rejected or modified.

In any experiment , the report on the experiment will be based on these guidelines and follows a sequence as shown in the following flow chart:

clip_image002

Inference

 

Early assessment that is carried out to answer the questions raised.

 

The inference should be written as :

…………………depend on…………………….

Or

The ……………..changes as the

……………changes

 

 

Hypothesis

 

A general statement about the relationship between a manipulated variable and a responding variable.

 

The hyphotesis should be written as :

The greater the………, the greater the…….

Or

The bigger the…………., the smaller the…..

 

Manipulated variable    

 

The quantity whose values we deliberately choose to change or a primary variable which causes other secondry variable to change.

 

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

 

List the apparatus and materials used so that at

least  a set  of data for manipulated and responding

variables can be determined.

 

State the arrangement of the apparatus that can

function by drawing a labeling diagram .

 

Procedure

 

State the method of controlling the manipulated variables

State the method of measuring the responding variables

Repeat the experiments at least four times.

 

Tabulating the data

 

Record the data in the following table

 

Manipulated variable

Responding variable

 

 

 

 

 

 

 

 

 

 

 

 

Analysing the data

 

Plot a graph of ( Responding variable) against

(Manipulated 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 responding variables must be written together with the units.

For example,

 

Velocity,v / s

 

 

 

 

 

 

 

Time , t / s

 

 

 

 

 

 

 

 

Volume , V / m3

Pressure , P / Pa

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The data shown in the table must be consistent in the number of decimal places in accordance with the respective measuring instruments.

For example,

Length, l / cm

Time , t /s

0

12.8

2

25.6

4

39.4

6

52.2

8

75.0

 

If the data too small or too big use the standard form number.

 

For example

Temperature q /oC

 

10

20

30

40

50

Density, r / kgm3

     x 104

9.7

8.5

7.3

6.6

5.1

 

How to plot the graph ?

                                                                 

The title of the graph must be shown.

The  axes of the graph must be labelled with the unit used.

For example:

clip_image004

The scale choosen must be easy to use.

Scales such  1:1  , 1:2  , 1:5  ,1:10  ,1:100  are preffered in plotting a graph.

Odd scales such as   1:3   , 1:4   , 1: 6  , 1:7  , 1: 30

should be avoided in plotting a graph.

 

Make sure the area covered by the plotted  points must not  be less than 50% of the area of the graph paper.

 

For example:

clip_image006

 

The scale on the axes must be uniform and clearly marked with value.

For example:

clip_image008

All the points are marked with a symbol such as a cross  or circle and the centre of the cross must

accurately positioned.              

                clip_image010                

 

The best straight line or the best curve graph must 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 smooth.                                                                                                                        

                clip_image012

 

It is not  advisable to plot graph by joining point to point because the graph obtained is not smooth.

clip_image014                                                                                                          

 

 

How to analyse the data ?

 

(a)     Determine the relationship between two variables.

Example :

               

  clip_image015
                                                                 

y  is directly proportional to x.

or   y  a x

      or   y = kx     k = constant

      or   y = mx    m = gradient

      or      y1   =     y2  

                          x1          x2  

                 

                                clip_image017

                                y  increases linearly with  x

      or    y = mx + c

                                 m =  gradient

                                 c  = intercept on axis-y

 

                                clip_image019                                                                                             

                                y  decreases linearly with  x

      or    y = -mx + c

                                 m =  gradient

                                 c  = intercept on axis-y

 

                                clip_image021

                                y is inversely proportional to x

      atau  y a 1

                                 x

      atau  y =  k

                                 x

                        k = constant

 

atau  y1  x1  =   y2  x2 

(b)           Determine the gradient of the graph

                Example

                clip_image023

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.

         clip_image025

 

(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.

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