Class 9 New Physics Chapter 1 Notes

Q1: What is the difference between physical and non physical quantities . 

Physical Quantities:
These are the quantities that can be measured using instruments. They have proper units.
Examples: Length, Mass, Time, Temperature.

Non-Physical Quantities:
These are the quantities that cannot be measured directly. They do not have standard units.
Examples: Feelings, Beauty, Intelligence, Honesty.

Q2: Define base and derived quantities.

Base quantities are the basic physical quantities that cannot be made from other quantities. They are the building blocks of all other quantities.
Examples: Length, Mass, Time.
Derived quantities are made by combining two or more base quantities using formulas.
Examples: Speed = Distance ÷ Time, Area = Length × Width

Q3: What is the difference between base unit and derived unit?

A base unit is the standard unit used to measure a base quantity. It is not made from any other unit.
Example: Meter (for length), Kilogram (for mass).
A derived unit is made by combining base units according to a formula.
Example: Meter per second (m/s) for speed, Square meter (m²) for area.

Q4: Define unit.

A unit is a standard quantity used to measure physical things. It tells us how much of something is present.
Example: If we say the length is 5 meters, ‘meter’ is the unit.

Q5: What is the System International of Units?

The System International (SI) of Units is a standard system used all over the world for measuring physical quantities. It helps scientists and people in different countries understand measurements in the same way.

Q6: Name seven base quantities with their units.

1. Length – meter (m)

2. Mass – kilogram (kg)

3. Time – second (s)

4. Temperature – kelvin (K)

5. Electric current – ampere (A)

6. Amount of substance – mole (mol)

7. Luminous intensity – candela (cd)

Q7: What are prefixes? Why are they used?

Prefixes are words added before units to show if the quantity is very big or very small. They make it easier to write and understand measurements.
Example: Kilometer = 1000 meters, Milligram = 0.001 gram

Q8: What is scientific notation? Why is it used?

Scientific notation is a way to write very big or very small numbers easily using powers of 10.
Example: 5000 = 5 × 10³, 0.0001 = 1 × 10⁻⁴
It is used to make writing and reading such numbers simple and clear.

Q9: What is Vernier Caliper? Why is it used? Write its least count.

Vernier caliper is a measuring tool used to measure small lengths very accurately. It is used because it gives more accurate measurements than a simple ruler.
Least count: 0.01 cm or 0.1 mm.

Q10: What is zero error of vernier caliper?

Zero error is the error that occurs when the vernier caliper shows a reading even when it is fully closed (when it should show 0).

Q11: When is the zero error of vernier caliper positive or negative?

Positive zero error: When the vernier scale zero is ahead of main scale zero.
Negative zero error: When the vernier scale zero is behind main scale zero.

Q12: What is screw gauge? Why is it preferred over vernier caliper?

Screw gauge is a device used to measure very small thicknesses or diameters like wires. It is preferred over vernier caliper because it gives more accurate and precise results.

Q13: What is the least count of screw gauge?

The least count of screw gauge is 0.01 mm.

Q14: What is meter rule? What is its least count?

A meter rule is a long measuring stick used to measure length. Its least count is 0.1 cm or 1 mm.

Q15: What is physical balance? Where is it used?

A physical balance is an instrument used to compare the mass of two objects. It is used in labs for accurate mass measurement.

Q16: What is weighing?

Weighing means finding the mass of an object using a balance or scale.

Q17: What is a stopwatch? Write its types.

A stopwatch is a device used to measure time during experiments.
Types: Mechanical stopwatch, Digital stopwatch.

Q18: How does a mechanical stopwatch work?

A mechanical stopwatch works with a spring and gears. When pressed, the spring moves the hands to measure time.

Q19: What is a measuring cylinder? Write its uses.

A measuring cylinder is a container marked with units to measure the volume of liquids. Used in labs for measuring liquids or using water displacement.

Q20: What is displacement can method in cylinder measurement?

This method finds volume by measuring how much water is displaced when an object is put into water.

Q21: What are the types of errors in measurement?

Types: Human error, Systematic error, Random error

Q22: What is human error? How can it be reduced?

Human error happens due to mistakes by the person measuring. It can be reduced by careful reading and correct method.

Q23: What is systematic error? How can it be measured?

Systematic error happens due to faulty instruments or wrong method. It can be measured by checking with standard values.

Q24: What is random error? How can it be reduced?

Random error is unexpected and changes each time. It can be reduced by taking an average of many readings.

Q25: What is uncertainty in measurement?

Uncertainty means a small doubt in a measurement. It shows that no measurement is 100% exact.

Q26: What are significant figures? Write rules to find them.

Significant figures show how accurate a number is.
Rules:

1. All non-zero digits are significant.

2. Zeros between digits are significant.

3. Leading zeros are not significant.

4. Trailing zeros after decimal are significant.

Q27: Write the rules to round off digits.

1. If the digit after rounding place is less than 5, leave the digit.

2. If it is 5 or more, increase the digit by 1.

Q28: Difference between precision and accuracy.

Precision means getting the same result again and again.
Accuracy means getting the result close to the true value.

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