Blog Cikgu Rose: Physics..Biology..Science

CHAPTER 1 : 1.5 SCIENTIFIC INVESTIGATION

1.5 SCIENTIFIC INVESTIGATION

LEARNING OUTCOMES:

A student should be able to :

1. Identify variables in a given situation,

2. identify a question suitable for scientific investigation,

3. form a hypothesis,

4. design and carry out a simple experiment to test the hypothesis,

5. record and present data in a suitable form,

6. interpret data to draw a conclusion,

7. write a report of the investigation.

a) A scientific investigation begins with observation. When observing,

we come out some questions. (i.e : hearing, smelling, touching,

tasting, seeing)

b) Making inference is a early assessment or explanation that is

carried out to answer the question raised. Inference is an early conclusion to what we observed

c) Form a hypothesis which is the statement of relationship between

the manipulated variable and the responding variable we would

expect.

d) Aim has to be stated so that all the investigating effort is centred

on the main subject.

e) Identify all the variables ;

i ) Manipulated variable is a quantity we manipulate /

variable which causes other secondary variables to change.

ii) Responding variable is the quantity which is affected by the

manipulated variable and is measured experimentally.

iii) Fixed variable is the quantity that does not change

throughout the experiment.

f) Apparatus / Materials needed to be listed according its specification

example measuring instrument to ensure the success the

experiment.

g) Procedure is the sequence of action or operation in order to carry

out the experiment according to the instructions given.

h) Observation is the listing and tabulation of all data obtained in the

experiment.

i) Analysing of data can be carried out by plotting the graph, followed

by the interpretation of graph or calculation to obtain the required

value.

j) Discussion needs to be stated to find out whether the result obtained support the stated hypothesis. Precautions of the experiment can be suggested to overcome the weakness, to reduce the experimental error or to improve the result of the experiment.

k) A conclusion is stated concerning the result of the experiment

(is written in accordance with the aim of the experiment and based on graph).

By comparing with the aim stated, this will determine

whether the hypothesis is accepted or rejected.

CHAPTER 1 : ACCURACY & CONSISTENCY

Accuracy and Consistency in Measurements

1.4.1 Accuracy

1. ___________ of a measurement is how close the value of a measurement

to the ____________ value.

2. The level of accuracy is related to the relative error.

3. An error is a between the measured value and the actual

value .

4. Accuracy can be improved by : -

(a) repeated readings are taken and the average value is calculated

(b) avoid parallax errors

(d) use measuring instruments with a higher accuracy.

For example, a vernier callipers is more accurate than a ruler

1.4.2 Consistency

1. / Precision of an instrument is the ability of the instrument

to measure a quantity with little or no deviation among measurements.

2.. A measurement is considered consistent will have a relative

deviation or no deviation from the average value .

3. A deviation is a difference between a _______________value and its

average value .

4. average deviation = Total deviation

__________________

number of value taken

5. relative deviation = average deviation x 100 %

______________

average value

6. Consistency can be improved by

(a) eliminating parallax errors

(b) exercising greater care and effort when taking readings.

7. Comparisons between consistency and accuracy by considering a target.

Example:

A student used vernier callipers to measure diameter of a glass rod. The table below shows the readings.

Measurement	Diameter rod (cm)	Deviation
1	2.23	0.012
2	2.26	0.018
3	2.24	0.002
4	2.23	0.012
5	2.25	0.008
Average	2.242	0.01

Relative deviation = ( 0.01 / 2.242) x 100%

= 0.45 %

1.4.3 Sensitivity in Measurements

1. Sensitivity of an instrument is its ability to detect a small change in the

quantity to be measured.

2. A measuring instrument that has a scale with a smaller divisions is more

sensitive .

3. Measuring instruments.

Measuring instruments	Smallest magnitude of quantity (cm)	Sensitivity / Accuracy
Metre rule	0.1	0.1 cm (low)
Vernier callipers	0.01	0.01 cm (moderate)
Micrometre screw gauge	0.001	0.001 cm (high)

1.4.4	Errors in Measurements
	1. An error is the difference between the measured value and the actual value. 2. There are two main types of errors in measurements, A. systematic errors B. random errors. A. Systematic errors i. The error in calibration of instrument which makes the instrument defective. (We must examine the instrument carefully before using them) ii. ________ error which means the pointer of the instrument does not return to zero when not in use. ( Zero error can be corrected by compensating the readings) iii. A problem which persists throughout the experiment such as repeated error in reaction time and wrong assumption. Systematic errors will lead to decrease in
	B. Random errors i. Arise from unknown and unpredictable variations in condition, and will produce a different error every time you repeat the experiment. ii. May be due to: (a) personal error (human limitations of sight and touch) (b) lack of sensitivity ( instrument does not respond / indicate insignificant or small change ) (c) natural errors ( wind , temperature, humidity, refraction, magnetic Field or gravity ) (d) wrong technique ( applying excessive pressure when turning a micrometer screw gauge ) iii. Can be minimized by repeating the measurement several times and taking the average (mean) of the reading . iv. Parallax error An error in reading a measurement because an observer’s eye and the pointer are not in a line perpendicular to the plane of the scale . (the eyes of the observer must be align and perpendicular to the scale of measuring instrument)