8th Science Guide Unit 1 Measurement

8th Standard Science  Guide Lesson 1 Measurement | English Medium

8th Science Guide Unit 1 Measurement book back answers. 8th Standard Science Guide English Medium Book Back Answers. 8th Science Samacheer kalvi guide Tamil Medium and English Medium Book Back and additional questions and answers. 8th Text Book download pdf. 8th std All Subject Guide. 

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8th Science Guide Unit 1 Measurement

I. Choose the best answer

1. Which one the following system of units is the British System of unit?

1. CGS
2. MKS
3. FPS
4. SI

Ans : FPS

2. Electric current belongs to ______ quantities

1. base
2. supplementary
3. derived
4. professional

Ans : base

3. SI unit of temperature is

1. celsius
2. fahrenheit
3. kelvin
4. ampere

Ans : kelvin

4. Amount of substance is

1. directly proportional to the number of atoms
2. inversely proportional to the number of atoms
3. directly proportional to the square of number of atoms
4. inversely proportional to the square of number of atoms

Ans : directly proportional to the number of atoms

5. Luminous intensity is the intensity of

1. Laser light
2. UV light
3. visible light
4. IR light

Ans : visible light

6. Which one of the following devices is used to measure electric current

Measurement Book Back Solution

Ans : b

7. SI unit stands for

1. International system of units
2. Integrated System of units
3. International symbol of units
4. Integrated symbol of units

Ans : International system of units

8. Closeness of two or more measured values is called as

1. accuracy
2. precision
3. error
4. approximation

Ans : precision

9. Quantities other than base quantities are called as

1. supplementary quantities
2. derived quantities
3. professional quantities
4. energy quantities

Ans : derived quantities

10. Which of the following statements about approximation is wrong?

1. Approximation gives accurate value.
2. Approximation simplifi es the calculation.
3. Approximation is very useful when little information is available.
4. Approximation gives the nearest value only.

Ans : Approximation gives accurate value.

II. Fill in the blanks.

1. The solid angle is measured in _______. Ans : steradian
2. _______ recognized the need of ‘Standard Units’ for physical quantities. Ans : International system of units

3. The coldness or hotness of a substance is expressed by _______. Ans : temperature
4. _______ is used to measure electric current. Ans : Ammeter
5. _______ of substance, contains 6.023 × 10+23 atoms or molecules. Ans : One mole
6. Luminous Intensity is the amount of visible light, that is emitted in unit area per unit _______. Ans : solldangle

7. Quartz clock uses _______ oscillations. Ans : electronic
8. The uncertainty in measurement is called as _______. Ans : errors
9. _______ is the closeness of the measured value to the original value. Ans : Accuracy
10. The intersection of two straight lines gives us_______. Ans : plane angle

III. True or False.

1. SI units are metric system of units. Ans : True
2. Temperature is a measure of total kinetic energy of the particles in a system. Ans : False

Cu. An. : Temperature is a measure of average kinetic energy of the particles in a system.

3. In thermometers, freezing point of water is taken as the Upper Fixed Point. Ans : False

Cu. An. : In thermometers, bollling point of water is taken as the Upper Fixed Point.

4. One coulomb of charge flowing per minute is called ‘ampere’. Ans : False

Cu. An. : One coulomb of charge flowing per second is called ‘ampere’

5. Amount of substance gives the number of particles present in the substance. Ans : True
6. Intensity of light from a candle is approximately equal to one ‘candela’. Ans : True
7. Angle formed at the top of a cone is an example of ‘Plane Angle’. Ans : False

Cu. An. : Angle formed at the top of a cone is an example of ‘Solld Angle’.

8. Quartz clocks are used in GPS Devices. Ans : False

Cu. An. : Atomic clocks are used in GPS Devices.

9. Candela is used to express electric field intensity. Ans : False

Cu. An. : Candelais used to express light intensity.

10. The number 4.582 can be rounded off as 4.58. Ans : True

IV. Match the following:

1. Temperature – Closeness to the Actual Value
2. Plane Angle – Measure of hotness or coldness
3. Solid Angle – Closeness to two or more measurements
4. Accuracy – Angle formed by the intersection of three or more planes
5. Precision – Angle formed by the intersection of two planes

Ans: 1 – b, 2 – e, 3 – d, 4 – a, 5 – c

V. Assertion & Reason.

1. Direction : Mark the correct choice as

1. If both assertion and reason are true and reason is the correct explanation of the assertion.
2. If both assertion and reason are true but reason is not the correct explanation of the assertion.
3. Assertion is true, but reason is false.
4. Assertion is false, but reason is true.
5. Assertion : The SI system of units is the suitable system for measurements.

Reason: The SI unit of temperature is kelvin.

Ans: If both assertion and reason are true and reason is the correct explanation of the assertion.

 

2. Assertion : Electric current, amount of substance, Luminous Intensity are the fundamental physical quantities.

Reason: They are independent of each other.

Ans: Assertion is true, but reason is false.

3. Assertion : The seconds hand of a clock is having least count of one second.

Reason: Least count is the maximum measurement that can be measured accurately by an instrument.

Ans : If both assertion and reason are true and reason is the correct explanation of the assertion.

4. Assertion : Avogadro’s number is the number of atoms in one mole of substance.

Reason : Avogadro’s number is a constant

Ans : If both assertion and reason are true but reason is not the correct explanation of the assertion.

5. Assertion : Radian is the unit of solid angle.

Reason : One radian is the angle subtended at the centre of a circle by an arc of length equal to its radius.

Ans : Assertion is false, but reason is true.

 

VI Answer in a word or two (Very Short Answer):

1. What is the unit of mass in FPS system?

• Pound

2. How many base quantities are included in SI system?

• 7

3. Give the name of the instrument used for the measurement of temperature.

• Thermometer

4. What is the ‘Lower Fixed Point’ of the Fahrenheit scale?

• 32°F

5. What is the SI unit of Luminous Intensity?

• Candela

6. What is the value of Avogadro’s number?

• 6.023×1023

7. What type of oscillations are used in atomic clocks?

• Perlodic vibrations occuring within the atom

8. Mention the types of clocks based on their display.

• Analog clocks
• Digital clocks

9. How many times will the ‘minute hand’ rotate in one hour?

• one time

10. How many hours are there in a minute?

• 60 minutes = 1hour

VII Answer the questions given below (Short Answer):

1. What is measurement?

• Measurement is the process of finding an unknown physical quantity by using a standard quantity.

2. Name some common systems of measurement.

• FPS – System (Foot for length, Pound for mass and Second for time)
• CGS -System (Centimetre for length, Gram for mass and Second for time)
• MKS – System (Metre for length, Kilogram for mass and Second for time)

3. Define- Temperature.

• Temperature is a measure of the average kinetic energy of the particles in a system.

4. Define – ampere.

• One ampere is defined as one ‘coulomb’ of charge moving in a conductor in one second

5. What is electric current?

• Flow of electric charges, in a particular direction is known as ‘electric current’.
• The magnitude of an electric current is the amount of electric charges flowing through a conductor in one second.

I = Q / t

6. What is luminous Intensity?

• The measure of the power of the emitted light, by a light source in a particular direction, per unit solid angle is called as Luminous Intensity.

7. Define – mole.

• Mole is defined as the amount of substances which contains 6.023×1023 entities.

8. What are the differences between Plane angle and solid angle?

Plane Angle	Solid Angle
1. Angle between the intersection of two lines or planes	Angle between the intersection of three or more planes at a common point
2. It is two dimensional	It is three dimensional
3. Unit is radian	Unit is steradian

9. What are errors?

• The value of every measurement contains some uncertainty. These uncertainties are called as ‘Errors’.

 

VIII Answer in detail:

1. List out the base quantities with their units.

Quantity	Unit	Symbol
Length	metre	m
Mass	kilogram	kg
Time	second	s
Temperature	kelvin	K
Electric Current	ampere	A
Amount of Substance	mole	mol
Luminous Intensity	candela	cd

2. Write a short note on different types of clocks.

Types of clocks based on display:

• Analog clocks
• Digital clocks

Analog clocks:

It looks like a classic clock. It has three hands to show time.

• Hours hand: It is a short and thick it shows ‘hour’.
• Minutes hand: It is long and thin.it shows ‘minute’
• Second’s hand: it is long and very thin it shows ‘second’.it makes one rotation in one minute and 60 rotations in one hr.

Digital clocks

• A digital clocks displays the time directly. It shows the time in numerals or other symbols.
• It may have a number 12 hours or 24 hours display. Recent clocks are showing date,day,month,year,temperature,etc.,
• Digital clocks are often called as electronic clocks Types of clocks based on working mechanisms

Quartz clock:

• This clocks are activated by ‘electronic oscillations’ which are controlled by a ‘quartz crystals’
• The frequency of a vibrating crystal is very precise. So the quartz clock is more accurate than the mechanical clock.
• These clocks have an accuracy of one second in every 109 seconds.

Atomic clocks:

• these clocks are making use of periods vibrations occurring within the atom.
• these clocks have an accuracy of one second in every 109 seconds.
• Atoms clocks are used in global positioning system (GPS),Global Navigation satellite system (GIONASS) and international time distribution services.