Matric: Physics Chapter 2

CHAPTER 2- MEASUREMENTS

Measurements
Precision, Accuracy and Sensitivity
Precision Accuracy SensitivitY:
The consistency of readings taken (lower relative deviation).
To increase precision:
-         use a magnifying
-         glass when reading the scale
-         avoid parallax errors
How close the readings taken are to the actual value.
To increase accuracy:
-         use more sensitive equipment
-         repeat readings taken
-         avoid parallax errors
-         avoid zero errors or end edge errors
The ability of a measuring apparatus to detect small changes of the physical quantity.
To increase sensitivity: (e.g. mercury thermometer)
-         thinner bulb glass wall
-         narrower capillary tube
-         smaller bulb size

Measuring Apparatus
Using vernier calipers:
Vernier calipers (±0.01cm)

Main Scale: Each scale division on the main scale is equal to 0.1 cm
Vernier Scale:
The length of the vernier scale is equal to 0.9 cm.
There are ten divisions on the vernier scale, so the difference between one division on the main scale and one division on the vernier scale is 0.01 cm
Therefore, the sensitivity of a vernier caliper is 0.01 cm
How to make a reading:
•  First, note down the value on the main scale just before the ‘0’ mark on the vernier scale.
•  Next, observe which mark on the vernier scale is in line with the main scale.
Using a micrometer screw gauge:

Every marking here represents integer INCREMENTS. Therefore, the sensitivity of a micrometer screw gauge is 0.01 mm
A full turn of the thimble is equal to 0.5 mm
Every marking here represents 0.5 mm after the integer increments
How to make a reading:
•  Record the marking on the sleeve just before the thimble
• Observe the marking on the thimble that is in line with the middle line on the sleeve.
Micrometer screw gauge (±0.01mm)




Errors
Systematic Errors
Systematic errors are errors that can consistently affect readings. It cannot be reduced by taking the  average of multiple readings.
•  Zero errors
•  End error
•  Incorrect scale calibration
•  Human reaction time


Random Errors
Random errors happen when one reading deviates from the others. It can be reduced by taking the average from multiple readings.
•   Parallax errors
•   Unavoidable small changes in the surrounding
•   Outside disturbances that cannot be taken into account
•   Lack of sensitivity of the measuring instruments
•   Human errors, e.g:
Counted wrong number of oscillations.
Readings with inconsistent time intervals.
Volume of liquid was measured after some was unknowingly and unintentionally spilt.
Scientific Investigation
-         Making an inference
-         Making a hypothesis
-         Identifying the variables
-         Conducting the experiment
-         Recording and tabulating the data
-         Analyzing the data
-         Forming a conclusion

1. Meter

The length of the path traveled by light in vacuum in 1/299,792,458 of a second is known as meter.
Length is a fundamental unit used for measurements of length, distance and height. It is equal to the distance between two marks on a Platinum-Iridium bar kept at 0 C in International Bureau of Weight and Measurements (IBWM) near Paris.

2. Kilogram

The mass of a Platinum-Iridium cylinder kept at 0 C in International Bureau of Weight and Measurements (IBWM) near Paris is considered to be 1 kilogram.
Kilogram is a fundamental unit used for measurements of mass.

3. Second

It is equal to the duration of 9,192,631,770 periods of radiation of Cesium-133 in ground state.