Class 9 Physics Notes chapter 1 2025
Class 9 Physics Notes chapter 1 2025 will be shared. We will solve comprehensive questions. We will discuss base and derived units, Vernier callipers and micrometer screw gauge, different types of errors and precision and accuracy.
Q 1.1 What is meant by base and derived quantities ? Give the names and symbols of SI base units.
The quantities which are independent of the other physical quantities are called base quantities. We cannot define any base quantity in terms of any other quantity.
Derived quantities are the quantities which can be defined with reference to base quantities.
There are seven base physical quantities and hence seven base units. Symbol of meter is m, kilogram is kg, second is s, kelvin is K, ampere is A, candela is cd and mole is mol.
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Q 1.2 Give three examples of derived units in SI. How are they derived from base units ? Describe briefly.
Some of the derived physical quantities are area, volume and speed and there units are square meter, cubic meter and meter per second respectively.
When we multiply or divide two or more than two base units, we get derived units. Remember that by adding or subtracting base units, we cannot get a derived unit.
$$Area\;=\;Length\;\times\;breath\\=\;meter\;\times\;meter\\=\;Square\;meter\;=\;m^2$$
$$Volume=Length\times breath\times height\\=\;meter\;\times\;meter\;\times\;meter\\=\;Cubic\;meter\;=\;m^3$$
$$Speed\;=\;\frac{dis\tan ce}{time}\\=\frac{meter}{second}=\;m\;s^{-1}$$
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Q 1.3 State similarities and differences between Vernier Callipers and micrometer screw gauge.
Similarities between Vernier Callipers and micrometer screw gauge:
Similarities
Vernier callipers and micrometer screw gauge both are measurement instruments and are also more accurate than meter rod.
They both have a main scale and a secondary scale and also measure in milli meters. Usually, we use metals to make them.
Differences
Least count of Vernier callipers is 0.1 mm and least count of screw gauge is 0.01 mm.
Design of vernier callipers and screw gauge is totally different with each other.
Vernier callipers has jaws but screw gauge has spindle.
Screw gauge measures only external dimensions where as Vernier callipers measures external as well as internal dimensions.
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Q 1.4 Identify and explain the reasons for human errors, random errors and systematic errors in experiments.
There are three types of experimental errors. Human errors, systematic errors and random errors.
Identifications of errors
Human error
We can easily identify human error by checking the readings of results.
For example there is a huge difference between 5 cm and 0.5 cm.
Systematic error
We can identify systematic error by carefully checking the equipment.
For example zero error in vernier callipers is a systematic error.
Random error
We can identify a random error when every time our measurements are slightly different with each other.
For example if we measure a pen three times and get 11 cm, 11.1 cm and 11.2 cm.
Reasons for errors
Human error
Human errors occur due to personal performance.They can also happen due to recording wrong value during the experiment and poor timing.
Systematic error
Systematic error occurs because of zero error of instrument, poor calibration of instrument or incorrect marking. It can also happen due to consistent mistakes in the experimental setup.
Random error
Random error usually occurs due to sudden change in the environmental conditions and measuring instrument. It can also happen due to different actions of a man, who is performing the experiment.
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Q 1.5 Differentiate between precision and accuracy of a measurement with examples.
Precision
Precision of measurement means the measurements that are very close to each other.
It is determined by the instrument. The smaller the least count, the more precise is the measurement.
The measurements 99.9, 100.1 and 100.2 are precise measurements though the true measurement is 90.
Accuracy
Accuracy of a measurement refers how close the measured value is to accepted or true value.
Significant figures tell us about accuracy. The larger the number of significant figures, the higher is the accuracy.
The measurements 98,101 and 102 are accurate measurements if true value is 100.
The measurement 99.9, 100.1 and 100.2 are precise as well as accurate measurements if true value is 100.
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Check! Some useful links below
You tube channel 9th Class New book Sir Najam
Physics Chapter 2 New book 2025 Long Questions
9th Physics Chapter 1 2025 Short Question Answer
Class 9th Physics New Book 2025 Chapter 1 Numerical
Home Page Notespunjab.com
