measuring instruments ruler 1 a ruler is used to measure lengths from a few cm up to 1 m. a metre...

Measuring Instruments

Ruler 1 A ruler is used to measure lengths

from a few cm up to 1 m. A metre rule has an accuracy of 0.1 cm (i.e. 1 mm).


Ruler 2 Precautions to be taken when using a ruler: (a) Ensure that the object is in contact with the ruler to

avoid inaccurate readings. (b) Avoid parallax errors.


Ruler Parallax errors in measurement arise as a result of taking

a reading, with the eye of the observer in the wrong position with respect to the scale of the ruler. Figure 1.7 shows the correct position of the eye when reading the scale.

Error = 0.1 cmError = 0.1 cm


Ruler (c) Avoid zero and end errors. The ends of a ruler, which may be worn out, are a source

of errors in measurement. Thus it is advisable to use the division mark `1' of the scale as the zero point when taking a measurement.


Ruler (c) Length of the block, l =3.2cm-1.0cm = 2.2 cm


1 Lengths smaller than 1 mm can be measured with the help of an instrument called a vernier

caliper.

Vernier Caliper


Vernier Caliper 2 A vernier caliper is used to measure an

object with dimensions up to 12 cm with an accuracy of 0.01 cm.


Vernier Caliper 3 There are two pairs of

jaws, one is designed to measure linear dimensions and external diameters while the other is to measure internal diameters.


Vernier Caliper 4. To measure with a vernier caliper, slide the

vernier scale along the main scale until the object is held firmly between the jaws of the caliper. The subsequent steps are as follows.

Measuring Instruments Vernier Caliper (a)The reading on the main scale is determined with

reference to the `0' mark on the vernier scale. The reading to be taken on the main scale is the mark preceding the Figure 1.10 shows that the '0' mark on the vernier scale lies between 3.2 cm and 3.3 cm. The reading to be taken on the main scale is 3.2 cm (the `0' mark on the vernier scale acts as a pointer).

1


Vernier Caliper (b) The reading to be taken on the vernier scale is indicated by the

mark on the vernier scale which is exactly in line or coincides with any main scale division line. Figure 1.10 shows that the fourth mark on the vernier scale is exactly in line with a mark on the main scale. Thus the second decimal reading of the measurement is:

Vernier scale reading = 4 x 0.01 cm = 0.04 cm

2


Vernier Caliper (c) The reading of the vernier caliper is the result of

the addition of the reading on the main scale to the reading on the vernier scale.

3.2

0.04


Vernier Caliper (c) The reading of the vernier caliper is the result of

the addition of the reading on the main scale to the reading on the vernier scale.

Caliper reading = Main scale Reading + Vernier scale reading

Thus the reading of the vernier caliper in Figure 1.10 is = 3.2 + 0.04 = 3.24 cm

3.2

0.04


Vernier Caliper 5. A vernier caliper has a zero error if the `0'

mark on the main scale is not in line with the '0' mark on the vernier scale when the jaws of the caliper are fully closed


Vernier Caliper (a) Positive zero error Zero error = +0.04 cm. {0.40 – 0.36=+0.04cm}


0.72 cm

0.70 cm

0.02cm


Vernier Caliper

(b) Negative zero error Zero error = -0.02 cm.


Micrometer Screw Gauge

1 A micrometer screw gauge is used to measure small lengths ranging between 0.10 mm and 25.00 mm.



2 This instrument can be used to measure diameters of wires and thicknesses of steel plates to an accuracy of 0.01 mm.



3 The micrometer scale comprises a main scale marked on the sleeve and a scale marked on the thimble called the thimble scale.


Micrometer Screw Gauge 4 The difference between one division on the upper scale

and one division on the lower scale is 0.5 mm.


Micrometer Screw Gauge5 The thimble scale is subdivided into 50 equal divisions.

When the thimble is rotated through one complete turn, i.e. 360, the gap between the anvil and the spindle increases by 0.50 mm.

Measuring Instruments Micrometer Screw Gauge

6 This means that one division on the thimble scale is = 0.01 mm.

50

5.0 mm



7 When taking a reading, the thimble is turned until the object is gripped very gently between the anvil and the spindle.



8 The ratchet knob is then turned until a `click' sound is heard.


Micrometer Screw Gauge9 The ratchet knob is used to prevent the user

from exerting undue pressure.



10 The grip on the object must not be excessive as this will affect the accuracy of the reading.


Micrometer Screw Gauge11 Readings on the micrometer are taken as follows.(a) The last graduation showing on the main scale

indicates position between 2.0 mm and 2.5 mm. Thus the reading on the main scale is read as 2.0 mm.


Micrometer Screw Gauge11 Readings on the micrometer are taken as follows.

(b) The reading of the micrometer screw gauge is the sun of the main scale reading and the thimble scale reading which is:

2.0 + 0.22 =2.22 mm


Micrometer Screw Gauge 11 Readings on the micrometer are taken as follows.(b) The reading on the thimble scale is the point where the

horizontal reference line of the main scale is in line with the graduation mark on the thimble scale Figure 1.15(b) shows this to be the 22nd mark on the thimble scale, thus giving a reading of 22 x 0.01 mm = 0.22 mm.


Micrometer Screw Gauge12 Readings on the micrometer are taken as follows.

(a) Positive zero error In Figure 1.16, the horizontal reference line in the main

scale is in line with the 4th division mark, on the positive side of the `0' mark, on the thimble scale. The error of +0.04 mm must be subtracted from all readings taken.

Zero error = +0.04 mm


Micrometer Screw Gauge 13(b) Negative zero error

In Figure 1.17, the horizontal reference line on the main scale is in line with the 3rd division mark, below the `0' mark of the thimble scale.

Zero error = -0.03 mm

Chapter 1

1.5 ANALYSING SCIENTIFIC INVESTIGATION


1. The investigative procedure begins with the following steps:

Making an inference To interpret or explain what is being observed. It is also

an early conclusion based on observation.

1.5 ANALYSING SCIENTIFIC INVESTIGATION Determining the variables A variable is a physical quantity which varies/changes

during the course of a scientific investigation.


In a scientific investigation, there are 3 different types of variables, namely:

(a) Manipulated variable • It is a physical quantity which is fixed in an experiment. (b) Responding variable • It is a physical quantity which depends on the

independent variable. (c) Constant variable • It is a physical quantity which is fixed while an

experiment is being carried out.


Making a hypothesis It is a clarification/explanation regarding the

relationship between the manipulated variable and the responding variable when all other variables are kept constant.

A hypothesis must be proven correct after an

experiment is carried out.


Controlling the variable The experiment must be conducted in an

appropriate place so as not to influence the variables.


Planning the investigative procedure/method Covers the choice and arrangement of the

apparatus together with the work procedure being followed/ conducted.


Collecting data in tabular form Data in the same strips (i.e., rows and columns)

must have the same units and the same number of decimal places (ie., data must be consistent).

For example:


1. The investigative procedure begins with the following steps:

Collecting data in tabular form For example:


Interpreting the data It is a result/decision that is made by way

of the experiment.


Making a conclusion It is a record that is made regarding an

information that is being studied based on the aim of the experiment.

The conclusion which is made is based on the shape of the graph that is plotted and also on the value(s) of the quantities obtained through calculation using a formula.


Making a complete report of an experiment A complete report of an experiment must cover

all the following aspects: • Problem statement • Inference • Hypothesis • Aim of experiment • Variables of the experiment • Arrangement of apparatus/Materials used


Making a complete report of an experiment • Experimental procedure - including the method

for controlling the manipulated and responding variables. • Tabulating data • Analyzing data • Making a conclusion • Data tabulation • Data analysis


Experiment 1.1 To Study The Relationship Between The Length

Of A Pendulum And The Period Of Oscillation of The Pendulum

Problem Statement How can the period of oscillation of a pendulum

be determined?


Experiment 1.1 To Study The Relationship Between The Length Of A

Pendulum And The Period Of Oscillation of The Pendulum

Hypothesis As the length of the pendulum increases, its period of

oscillation increases.


Variables (a) Manipulated : Length of pendulum (b) Responding : Period of oscillation (c) Constant: Amplitude of oscillation, mass of pendulum

bob (or weight) and acceleration due to gravity.


Experiment 1.1 Apparatus/Materials Used Pendulum bob, a 100cm length of thread, metre rule, 2

small pieces of wood, retort stand and a stop-watch.


Experiment 1.1 To Study The Relationship Between The Length Of A

Pendulum And The Period Of Oscillation of The Pendulum

Procedure


Experiment 1.1 To Study The Relationship Between The Length Of A Pendulum And

The Period Of Oscillation of The Pendulum Procedure 1. A 50.0g pendulum bob is tied to one end of a 100cm length

thread. 2. By using a retort stand and two small pieces of wood, the

other end of the thread is clamped as shown in Diagram 1.19. 3. The length, l of the pendulum is measured from the end

below the small piece of wood to the centre of the bob. (i.e., l = 20cm) 4. The pendulum is made to oscillate in a plane and having a

small amplitude of oscillation. (i.e., approximately 10°)


Procedure 5. The time taken to complete 20 full oscillations is recorded

with a stop-watch. 6. The time for 20 complete oscillations is recorded once more. 7. The average time taken in the above two steps is calculated,

so too with the time taken. 8. The experimental procedure is repeated by taking the length

of the pendulum to be l = 30cm, 40cm, 50cm, 60 cm and 70cm. 9. All readings obtained are recorded in a table. 10. Then, a graph of T against l is plotted.


Result:


Graph T against L:


Experiment 1.1

Discussion: Graph of period, T against length, L shows a curve with

positive gradient. Thus, as L increases, T also increases. Hence, the hypothesis is accepted.


Conclusion: The longer is the length of the pendulum, the longer is the

period of its oscillation.

measuring instruments ruler 1 a ruler is used to measure lengths from a few cm up to 1 m. a metre...

Documents

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