8th Std Science Solution in English | Lesson.1 Measurement

Lesson 1. Measurement

Lesson 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 is a ______quantity

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. Luminous intensity is the intensity of

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

Ans : visible light

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

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

Ans : precision

6. 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.

7. Luminous intensity is the intensity of ______

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

Ans : derived quantities

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

Ans : b

9. 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

10. Quantities other than base quantities are called as

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

Ans : derived quantities

II. Fill in the blanks.

1. The solid angle is measured in _______.

Ans : steradian

2. The coldness or hotness of a substance is expressed by _______.

Ans : temperature 

3. _______ is used to measure electric current.

Ans : Ammeter

4. One mole of a substance contains _______ atoms or molecules.

Ans : International system of units

5. The uncertainty in measurement is called as _______.

Ans : errors

6. The closeness of the measured value to the original is _______.

Ans : Accuracy

7. The intersection of two straight lines gives us_______.

Ans : plane angle

8. _______ of substance, contains 6.023 × 10+23 atoms or molecules.

Ans : One mole

9. Luminous Intensity is the amount of visible light, that is emitted in unit area per unit _______.

Ans : solldangle

10. Quartz clock uses _______ oscillations.

Ans : electronic

11. _______ recognized the need of ‘Standard Units’ for physical quantities.

Ans : International system of units

III. State true or false. If false, correct the statement.

1. 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.

2. If one coulomb of charge is flowing in one minute, it is called ‘ampere’.

Ans : False

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

3. Amount of substance gives the number of particles present in the substance.

Ans : True

4. Intensity of light coming from a candle is approximately equal to one ‘candela’

Ans : True

5. Quartz clocks are used in GPS Devices.

Ans : False

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

6. 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’.

7. The number 4.582 can be rounded off as 4.58.

Ans : True

8. Candela is used to express electric field intensity.

Ans : False

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

9. SI units are metric system of units.

Ans : True

10. 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.

IV. Match the following:

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.

1. 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 : 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.

4. 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.

5. 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.

VI. Answer very briefly.

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

7

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

Thermometer

3. What is the SI unit of Luminous Intensity?

Candela

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

Perlodic vibrations occuring within the atom

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

• Analog clocks
• Digital clocks

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

one time

7. How many hours are there in a minute?

60 minutes = 1hour

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

Pound

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

32°F

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

6.023×10²³

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.

• Celcius scale
• Fahrenheit scale
• Kelvin scale

3. Define – ampere.

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

4. 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

5. What do you mean by 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.

6. Define – mole.

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

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

8. 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)

9. Define- Temperature.

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

10. 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.

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.

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