Matric Notes Physics 9th Ch 1 Physical Quantities & Measurements Long Questions

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Comprehensive Questions

Q.1 What is physics? Also, describe its important branches?

Answer: Physics: The branch of science which deals with the study of properties, energy and their mutual relationship is called physics”

Some important branches of physics are given below

1. Mechanics:-It deals with the motion of bodies under the action of the force.

2. Heat and thermodynamics:-It deals with the study of nature, properties. and uses of heat energy. And also deals with the transformation of heat energy from one to another form.

3. Optics:- It deals with the prorogation, reflection, refraction, dispersion, and wave properties of light.

4. Electricity and magnetism:- It deals with the study of charges at rest as well as in motion.

5. Atomic physics:-It deals with the structure and properties of an individual atom.

6. Nucleus physics:- It deals with the structure and properties of the nuclease of an atom.

7. Solid-state physics:-It deals with the properties of matter in solid-state.

8. Particle physics:- It deals with the study of elementary particles.

9. Plasma physics:-It deals with the study of fourth state of matter. And occurs in an ionized state.

10. Quantum physics:- Quanta is studied is this branch which is the discrete and individuals particle of energy.

11. Semiconductor physics:- Whose properties lie b/w conductor and insulator.

12. Astrophysics:- It deals with the study of heavenly bodies.

13. Biophysics:- Study of biology based on the principle of physics is called biophysics.

14. Geo physics:- It deals with the study of earth and atmospheric.

15. Health physics:- It deals with the study of diseases and their treatment.

Q.2) Define physics. How physics play a crucial role in science technology and society?

Answer: “Physics is the branch of science, which deals with the study of properties of matter and energy along with their mutual interaction”.

The word ‘physics’ comes from the Greek ‘knowledge of nature,’ and in general, the field aims to analyze and understand the natural phenomena of the universe. It covers a wide range of phenomena, from the smallest atomic particle to largest galaxies.

Physics and technology are closely related however they are also different from each other. Physics is concerned with gathering knowledge and organizing it. Technology lets us use that knowledge for practical purposes. Behind every technology a physical phenomenon exists, Physics has played its part in the process of humankind and in the improvement of the quality of living.

Physics has provided a basic understanding of the development of new instruments. In biology, we have developed CT scan machines, MRI and laser surgeries. These technologies work on the principle of Physics i.e. resonance, magnetism and optics.

The use of Physics in information technology has improved the standard of communication. Mobile cell phones are commonly used even by illiterates. Hologram technology is a three-dimensional image, created with photographic projection. The hologram technology is also incorporated in cell phones.

Q.3) What is SI? Name SI base quantities and their units.

Answer: The complete set of units for all physical quantities is called the international system of units. SI stands for “System International“. SI units are based on seven base units which are as follows.

1. Base Quantity SI Unit
2. length meter
3. mass kilogram
4. time second
5. current ampere
6. temperature Kelvin
7. Intensity of light Candela
8. Amount of a substance mole

Q.4) What are physical quantities? Distinguish between base and derived physical quantities.

Answer: “All quantities that can be measured are called physical quantities”

Examples of physical quantities are mass, amount of substance, length, time, temperature, electric current, light intensity, force, velocity, density, and many others. A physical quantity is always measured of natural non-living objects. The foundation of physics rests upon physical quantities in term of which the laws of physics are expressed. Therefore, these quantities have to be measured accurately.

Types of physical quantities

i. Base physical quantities

ii. Derived physical quantities

Base physical quantities

“Those physical quantities in terms of which other physical quantities can be expressed are called base physical quantities”. There are seven base quantities which are given below

• Physical quantity Unit
• length meter
• mass kilogram
• time second
• current ampere
• temperature Kelvin
• Intensity of light Candela
• Amount of a substance mole

Derived physical quantities

“Those physical quantities which are derived from base quantities are called derived physical quantities”. There are several derived quantities few of which are given below

1. Physical quantity Unit
2. area square meter
3. volume cubic meter
4. speed, velocity meter per second
5. acceleration meter per second squared
6. force Newton = kilogram meter per second squared
7. density kilogram per cubic meter
8. pressure Pascal = kilogram per meter per second squared

Q.5) What is standard form or scientific notation?

Answer: Scientific notationis an internationally accepted way of writing numbers. With the help of it, we can write very large or very small numbers in the power of 10 with only one non zero digit before the decimal.

In physics, we deal with very large or very small numbers. For example the mass of moon is 70,000,000,000,000,000,000,000 kilograms. Unisg this number occasionally will create a mess. To avoid this mess we use a standard form or scientific notation. It represents a number as the product of a number greater than 1 and less than 10 (mantissa) and a power of 10 (exponent).

number (N) = mantissa (M) x 10exponent (n)

The mass of the moon can thus be written compactly as 7 x 1022 kg, where 7 is the mantissa and 22 is the exponent.

Q.6) What are prefixes? Explain with examples.

Answer: A mechanism in which a very small or very large number is expressed as in the form of power of ten by giving a proper name to it is called prefix to the power of ten.

Prefix makes standard form to be written even more easily. Large number are simple written in more convenient prefix with units.

The thickness of a paper can be written conveniently in smaller units of millimeters instead of meter. Similarly the long distance between two cities can be expressed in a bigger unit, i.e., kilometer. A useful set of prefixes in SI to replace powers of 10.

Q.7) Describe the construction and use for measurement of the following instruments:

a) Venire Calipers b) Screw gauge

Answer:

a) Venire Calipers

Definition: “A device used to measure a fraction of smallest scale division by sliding another scale over it is called vernier caliper”.

Vernier Callipers is used to measure small lengths, thickness, an internal and external diameter of a hollow cylinder, depth of an object with accuracy up to 0.1 mm or 0.01cm.

There are two scales on vernier calipers.

Main (fixed) Scale:

The main scale which has markings of usually of 1 mm each and it contains jaw A on its left end.

Vernier (sliding) Scale:

A vernier (sliding) scale which has markings of some multiple of the marking on the main scale. The vernier scale usually has the length of 9 mm and is divided equally into 10 divisions (thus the separation between two lines on vernier scale is 9/10 mm = 0.9 mm).

Suppose we want to measure the diameter of a small solid cylinder with vernier caliper we will use the following method.

1. Note the least count of the vernier, (it is usually written on vernier caliper, otherwise we can find it out by a method described previously) which in our case is 0.01 cm (0.1 mm).

2. Close the jaws fully with no object between the jaws. If the zero line of the vernier scale coincides with the zero lines of the main scale then there is no zero error.

3. Now fix the solid cylinder in between the two jaws and tighten the vernier with the help of screw ‘S’ suppose the zero of the vernier scale is to the right of 1.9 cm the mark and to the left of the 2.0 cm (20 mm) mark as shown in the figure1 shown below. Thus the required length is somewhat greater than 1.9 cm (19 mm).

4. To find the fraction to be added. We see that division of the vernier scale which coincides (inline) with any division of the main scale. As the 6th division of the vernier scale coincides with one of the main scale divisions as in the figure1 shown below.

5. Multiply the least count 0.01 cm (0.1 mm) by 6 which gives 0.06 cm (0.6 mm) and add to 1.9 cm (19 mm). The measured length is 1.9 cm + 0.06 cm = 1.96 cm or 19 mm+ 0.6 mm = 19.6 mm Hence the diameter of solid cylinder is 1.96 cm (19.6 mm)

Hence the diameter of a solid cylinder is 1.96 cm (19.6 mm).

b) Screw gauge

Definition: ” A device used to measure a fraction of smallest scale division by a rotatory motion of circular scale over it is known as screw gauge”.

The main objective of the Screw Gauge is to measure the diameter of a given object and its volume.

Parts of Screw Gauge (SG)

• Datum line / Central line
• Anvil
• Spindle
• Thimble (circular scale)
• Ratchet knob
• Sphere

If the pitch of the screw is 0.5 mm and the number of divisions on the circular scale is 50 then the diameter of a small sphere is measured by using a screw gauge by the following method.

1. Place the object between thimble and anvil. Now turn the thimble until the anvil and spindle gently grip the object. Then turn the ratchet until it starts to click. The ratchet prevents the user from exerting too much pressure on the object.

2. Read the main scale reading. For example, in the figure2 shown above the edge of circular scale is lying between 5.5 mm and 6.0 mm, i.e. the diameter of the sphere is more than 5.5 mm and less than 6.0 mm.

3. To know the part more than 5.5 mm. We look for the division of circular scale (Thimble scale) which is in front of the datum line. In the figure2 shown above, it is 28.

4. Now multiplying 28 by the least count which is 0.01 mm we get 0.28 mm. Add this product to 5.5 mm. 5.5 mm + 0.28 mm = 5.78 mm Thus 5.78 mm is the diameter of the sphere.

Q.8) What is meant by the significant figures of measurement? What are the main points to be kept in mind while determining the significant figures of a measurement?

Answer: It is defined as accurately known digits and first doubtful digit in a measurement is known as a significant figure.

Explanation

Consider we want to measure the length of a rod with the help of meter rod. We assume that three students measured the length as 9.63 cm, 9.62 cm and 9.64 cm. In this case, we agree with 10.6 cm, which we called accurately known digits. However, there is doubt about the third digit, which is 3, 2 and These digits are called doubtful digits. Out of three digits, two are accurately known while the third one is the doubtful digit.

Rules for determining significant figures

Following rules should be kept in mind while dealing with significant figures in a given data.

i. All non-zero numbers (1,2,3,4,5,6,7,8,and 9) are always significant.

ii. All zeroes between non-zero numbers are always significant.

iii. All zeroes, which are simultaneous to the right of the decimal point and at the end of the number, are always significant.

iv. All zeroes which are to the left of a written decimal point and are in a number ≥ 10 are always significant.

Number No of significant figures Rule(s)

• 48,923 5 1
• 3.967 4 1
• 900.06 5 1,2,4
• 8.1000 5 1,3
• 501.040 6 1,2,3,4
• 0.0004 (= 4X10-10) 1 1,4
• 3,000,000 (= 3X106) 1 1
• 1.222 x 10(6) = 1.22200000 x 10(6) 4 9

Rules for rounding of non-significant figures

We have following rules for dropping the non-significant figures

i. If the last digit is less than 5 then it will be ignored e.g. 84.74 is rounded to 84.7.

ii. If terminating digit is greater than 5 then the last digit increase by 1. e.g. 87.76 is rounded to 87.8.

iii. In case if dropping digit is 5 and the last retained digit is even then the last digit i.e. 5 will be dropped without affecting the next one. e.g. 77.65 is rounded to 77.6.

iv. And if the last digit is 5 and the 2nd last is an odd digit then the 2nd last digit is increased by1 in order to round off 5 e.g. 87.35 is rounded to 87.4.