Physical Quantities and Measurement - Physics For Class IX (Science Group) - Short Questions Answers And Self Assessment Questions

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Physics For Class IX (Science Group)
UNIT 1: Physical Quantities and Measurement
Short Questions Answers

Q.1: Define nature and science?
Ans: NATURE:
Nature is described as a pragmatic set of rules followed by all the things around us. It is something which is much greater than the imagination of humans. It is observable, it is surprising but it is somehow explainable, its architecture has been designed with very beautiful patterns, strict rules but with simplicity. A science which explores the nature is Physics

SCIENCE:
The word science refers to the study of a fact by collecting information through observation, presenting it in a mathematical way, justifying the idea with experiment and finally making a conclusion about the fact.

Q.2: Define Physics?
Ans: PHYSICS:
One of the most basic and ancient science is the Physics. Physics Derived from Ancient Greek ‘physicos’ meaning ‘knowledge of nature’.
Thus physics can be defined as:
Physics is the branch of science which deals with studies of matter its composition, properties, and interaction with energy.

OR

It basically deals with the behavior and structure of matter and the energy that derives the matter.

OR

Physics is the branch of natural science that studies matter, its motion, its behavior through space and time and the related entities of energy and force.

OR

Physics is the branch of science which observes the nature represents it mathematically and conclude with the experiment

Q.3: Why do we study physics?

• Physics is one of the most fundamental scientific disciplines, and its main goal is to understand how the universe behaves.
• It is a matter of fact that Physics can be considered as the mother of all sciences.
• The beauty of physics lies in its Laws that govern this whole universe from an atom to large scale galaxies and in its experiments from home to large scale experiment labs.

Q. 4: How many categories or types of Physiiscist are there? Define each.
Ans: TYPES OF PHYSICIST:
Physicist are categorized into two categories:

1. Theoretical physicist
2. Experimental physicists

THEORETICAL PHYSICIST:
Those who observe the nature solve its mysteries with available and missing information, present their theories with mathematical approach. They are known as theoretical physicist.

EXPERIMENTAL PHYSICIST:
Those who are more interested to test those theories with experiments are known as experimental physicists.

Q.5: Describe the crucial role of Physics in Science, Technology and Society? OR What is the importance of physics?
Ans: Importance of Physics in Science Technology and Society

• Society’s reliance on technology represents the importance of physics in daily life.
• Many aspects of modern society would not have been possible without the important scientific discoveries made in the past. These discoveries became the foundation on which current technologies were developed.
• Discoveries such as magnetism, electricity, conductors and others made modern conveniences, such as television, computers, smart phones, medical instruments, other business and home technologies possible.
• Moreover, modern means of transportation, such as aircraft and telecommunications, have drawn people across the world closer together all rely on concepts of physics.

Q.6: What do you know about scientific are physical instruments?
Ans: All physical quantities are either calculated mathematically or measured through an instrument. Scientist, Engineers, Doctors and others like blacksmith, carpenter, and goldsmith even the workers and ordinary human's measure those physical quantities with the help of instruments.
For instance,

• Doctor uses a thermometer to tell our body temperature.
• A carpenter uses the inch tape to measure the length of woods required for furniture.
• A puncture mender uses air gauges to check the air pressure in the tyre.
• Similarly, a chemical engineer uses hydrometer for describing the density of a liquid.
• Measuring the physical quantity correctly with instrument is not an easy task for scientist and engineers. Scientist are seriously concerned with the accuracy of the instrument and its synchronization.
• Moreover, the instrument they design mostly for their own sake of research which readably goes on to commercial market.
• Many of the instruments we use today are inventions of pioneers of science.
• Usually, the basic physical quantities that we use in our daily life are measured with basic and simple instruments.

Q.7: Define least count?
Ans: LEAST COUNT:
Use of every instrument is restricted by smallest measurement that it can perform which is called least count.

Q.8: Give the difference between fundamental unit and derived unit?
Ans: DIFFERENCE BETWEEN FUNDAMENTAL UNIT AND DERIVED UNIT

S.No	Fundamental unit	Derived Unit
1.	The physical quantities discovered from first hand knowledge are called fundamental units.	The unit of those physical quantities which are derived from fundamental physical quantities are called derived units.
2.	Fundamental units cannot be further reduced to elementary level; in fact, these are elementary units.	Derived units can be reduced to its elementary level, which are composed of fundamental units.
3.	Fundamental units cannot be expressed in terms of derived units.	Derived units can be expressed in terms of fundamental units.
4.	Only seven fundamental units exist in Metric System or SI system.	There exist a large number of derived units in Metric System.
5.	Examples of fundamental units are Length (Meter, m), Mass (Kilogram, kg), Time (Second, s), Temperature (Kelvin, K), Amount of substance (Mole, mole), Electric current (Ampere, A), Luminous intensity (Candela, cd)	Examples of few derived units are Velocity (m/s), Acceleration (m/s2), Momentum (kg m/s ), Force (N), Density (kg/m3), Energy (J), Power (W), etc.

Q.9: Define Zero Error ? Write down its types?
Ans: ZERO ERROR:
On closing the two jaws of vernier caliper, if the zero of the main scale does not coincide with the zero of the vernier scale, then the instrument has an error called zero error.
There ere two types of zero error:

1. Positive zero error
2. Negative zero error

1- Positive Zero Error:
If the zero of the vernier scale is on the right side of the zero of the main scale, then the zero error will be positive.
To calculate this zero error, check the vernier scale division (E) which exactly coincide with any main scale division. Then,

Zero error (Z.E) = E X L.C

In case of positive error, it is subtracted from the total reading.

2- Negative Zero Error:
If the zero of the vernier scale is on the left side of the zero of the main scale, then the zero error will be negative.
To calculate this zero error, check the vernier scale division (E) which exactly coincide with any main scale division. Then,

Zero error (Z.E) = (10 - E) X L.C

In case of negative error, it is added to the total reading.

Q.10: What is National Prototype Meter and Kilogram?
Ans: National Prototype Meter and Kilogram:
Each country that subscribed to the International Metric Convention was assigned one or more copies of the international standards; these are known as National Prototype Meter and Kilogram.

Q.11: What is physical balance? Write down its major parts and working? OR What is physical balance? How does it work?
Ans: PHYSICAL BALANCE:
The Physical balance is an instrument used for measurement of mass. It is mostly used in laboratory. It works on the principle of moments.

Parts Of Physical Balance:
It consists of:

• A light and rigid beam of brass
• A metallic pillar
• A wooden base
• Two pans
• A metallic pointer
• An ivory scale
• When the beam is horizontal the pointer remains on zero mark on the ivory scale.
• Plumb line
• Levelling Screw
• Glass box

Working:
The plumb line indicates whether the balance is horizontal. In ideal condition the plumb line is aligned with the end of the knob fixed with the pillar. The whole box has leveling screws at the bottom to set it to horizontal. The device is enclosed in a glass box to avoid wind effects.

Q.12: Describe the working of electronic balance? Or What is an electronic balance?
Ans: ELECTRONIC BALANCE:
The Electronic Balance or the digital mass meter is an electronic instrument configured with integrated circuits and it works on the principal of balancing the forces.
The device is turned on and set to zero then object is placed on the plate.
The reading on the screen gives the mass of object.
The electronic balance is available in different ranges of measurement such as micro gram, milligram and kilogram etc.

Q.13: What is meant by human reaction time?  OR Why we use light gates?
Ans: HUMAN REACTION TIME OR USE OF LIGHT GATES:
As analogue or digital or watch is operated by human manually i.e., they have to be started or stopped by hand. This causes a random error in measurement of time i.e called human reaction time. For most people human reaction time is about 0.3- 0.5 s. Therefore more accurate measurement of time intervals light gates can be used.

Q.14: Why are physicists concerned about the property of matter in term of its mass and space? Or Define matter and describe its types in term of their properties?

Ans: MATTER:
Physicist are concerned with a physical quantity, a property of matter which may help to define the nature of matter in terms of its mass and space.
Definition:
"Matter is anything that has mass and occupies space."

THREE STATES OF MATTER:
The three common phases or states of matter are:

1. Solid
2. Liquid and
3. Gas

1.Solid:
A solid maintains a fixed shape and a fixed size, even if same force is applied it not readily change its volume.
2. Liquid:
A liquid does not maintain a fixed shape it takes on the shape of its container. But, like a solid it is not readily compressible, and its volume can be changed significantly only by a large force.
3. Gas:
A gas has neither a fixed shape nor a fixed volume - it will expand to fill its container.

Q.15: What is Measuring Cylinder? How can we measure the volume of liquid by measuring cylinder?
Ans: MEASURING CYLINDER:
Measuring cylinder is a glass or plastic cylinder with a scale-graduated in cubic centimeters or milliliters (ml)

Uses:
It is used to find the volume of liquids.

Process To Measure Volume Of Liquid By Measuring Cylinder:

• The volume of liquids can be measured with the help of Cylinders, and Beakers.
• A volume of about a liter or so can be measured using a measuring cylinder.
• When a liquid is poured, it rises to a certain height in the cylinder.
• Most measuring cylinders have scales marked in milliliters (ml) or cubic centimeters (cm³).
• The level of liquid in the cylinder is noted and volume of the liquid is obtained.
• In order to read the volume correctly we should keep the eye in level with the bottom of the lower meniscus of the liquid surface.
• Angular observation may result a false reading of the volume.

Q.16: How will you find the volume of small stone?
Ans: The volume of the solid is measured in a experiment and then subtracted from the total volume.
Experiment:

• Take a measuring cylinder of 1 liter capacity at full place it in a beaker.
• Fill cylinder full with water.
• Pour a stone of irregular shape in it gradually.
• As we pour the stone in the cylinder, the water from cylinder drops into the beaker.
• Drop the stone in cylinder completely.
• Calculate the volume of water ejected out of cylinder.
• Volume of water ejected is the volume of the stone.

Q.17: How will you determine the thickness of a piece of wire?
Ans: The thickness of a piece of wire can be determined with the help of screw gauge.

Q.18: Which device will you choose to measure the length of a small cylinder?
Ans: We use Meter rule to measure the length of a small cylinder

Q.19: Choose a proper instrument (meter rule, Vernier calipers, screw gauge, physical balance stop watch, measuring cylinder) for the measurement of length, diameter, mass, time and volume in daily life activities.
Ans

Device	Physical Quantity
Meter rule	Length
Vernier calipers, Screw gauge	Diameter
Physical balance	Mass
Stop watch	Time
Measuring cylinder	Volume

Self Assessment Questions

Q.1: What instrument will you choose to measure height of your friend?
Ans: To measure the height of our friend, we can use a meter rule or inch tape. 
When our height is measured at the doctor's clinic, we usually stand next to a device called a stadiometer.
A stadiometer is a long ruler attached to the wall. It has a sliding horizontal headpiece that's adjusted to rest on top of our head. It's a quick way of accurately measuring our height.

Q.2: Can you describe how many seconds are there in a year?
Ans: There are in:

• 1 year = 365 days
• 1 day = 24 hours
• 1 hour = 60 minutes
• 1 minutes = 60 sec

Therefore
One year would equal 365 times 24 times 60 times 60 seconds
OR
1 year = 365 x 24 x 60 x 60 = 31, 536, 000 seconds

Q.3: Which instrument will you choose to measure your mass?
Ans: We will choose weighing machine to measure our weight. 
The scientific word for weight of an object on a scale is known as "mass".  Therefore here we can use the word "weight" and "mass" interchangeably because both are used in everyday language.
For example: "I weigh 70 kg" or " the car's mass is 1 tonne."
Bathroom scales are used to measure a person's weight. They can be analogue or digital. Bathroom scales usually show units in kilograms or grams.

Q.4: Can you tell if the size of a nucleus is up to 10^-15 m. What prefix shall we use to describe its size?
Ans: femto (f) or femtometer (fm) 

Q.5: How can you identify which gas is denser among the gases?
Ans: If the gas is denser, it has high density. So by calculating the density of different gases at constant volume, we can identify less denser or more denser gases.

Q.6: Can you tell how hot air balloon works?
Ans: In hot air balloon the gas inside the balloon is heated by using a burner. So the hot air inside the balloon becomes less dense than the surrounding cooler air. The less dense hot air has enough lifting power to cause the balloon to float and rise into the air.
In order to get back the hot air balloon down, the pilot opens the flap at the top of the balloon to let the hot air go outside and the cooler air takes its place. Thus the density of the air inside the balloon increases hence it slowly comes down.

Q7: Determine the number of significant figures in 00.6022009 and also write down it in scientific notation
Ans: There are 7 significant figures (i.e. 6022009) in given value.
Scientific Notation = 6.022009 x 10^-1

Reasons

1. Fill a tub with water to certain level and mark.
Put some ice in it and observe the water level carefully as well as floating or sinking. Remove the ice from the tub without being melt and put a balloon in it and then observe. Likewise, put a spoon in that tub and observe. Again put an empty can of coke and observe. Can you tell which of all four has more density? And which has more volume?
Reason:
When we put a spoon in that tub it sinks into water, while rest are float on the surface of water. Thus spoon is much denser than rest object and has more density.
Similarly Balloon occupies more space than ice, spoon or empty can of coke. Thus balloon has more volume than rest objects.

2. Why large weight woods floating on the surface of water and iron needle sinks into the water?
Reason:
Iron is “denser” than wood and have more density that is why iron needle sink into water and large weight woods floating on the surface of water.

3. Why the humans in 'Dead Sea' situated in Jordan does not sink while swimming?
REASON:
The humans in that sea while swimming does not sink! This is because the water of sea is much more salty than normal, which raises the density of water.

4. The large weight woods floating on the surface of water. However, an iron needle sinks into the water.
REASON:
Iron is “denser” than wood and water, where as wood is less dense than water that is why needle sinks into water while the large weight woods floating on the surface of water.

5. Why ice floats while a coin sinks in the water?
REASON:
Solid objects are denser and have more weight than liquids. Although ice is a solid but the water is heavier than ice, it displaces the lighter ice, causing the ice to float to the top.
While the coin have more density than the water, and so the coin sink. So anything with more density than water will sink in water, but other objects that have less density than water will float.

6. Which is more accurate Vernier Caliper or a Screw Gauge and why?
Ans: Screw Gauge is more accurate than Vernier Caliper:
REASON: As compare to Vernier calipers, screw gauge is more accurate and precise because a screw gauge can even measure dimensions smaller (such as the diameter of a wire or sphere) than those measured by a Vernier Caliper. The least count of Vernier calipers is 0.1 mm and for screw gauge it is 0.01 mm. So, a screw gauge can measure accurately up to one hundredth part of a millimeter and more accurate than a Vernier caliper.