8th Science Guide Unit 1 Measurement
8th Standard Science Guide Lesson 1 Measurement | English Medium
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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?
- CGS
- MKS
- FPS
- SI
Ans : FPS
2. Electric current belongs to ______ quantities
- base
- supplementary
- derived
- professional
Ans : base
3. SI unit of temperature is
- celsius
- fahrenheit
- kelvin
- ampere
Ans : kelvin
4. Amount of substance is
- directly proportional to the number of atoms
- inversely proportional to the number of atoms
- directly proportional to the square of number of atoms
- inversely proportional to the square of number of atoms
Ans : directly proportional to the number of atoms
5. Luminous intensity is the intensity of
- Laser light
- UV light
- visible light
- 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
- International system of units
- Integrated System of units
- International symbol of units
- Integrated symbol of units
Ans : International system of units
8. Closeness of two or more measured values is called as
- accuracy
- precision
- error
- approximation
Ans : precision
9. Quantities other than base quantities are called as
- supplementary quantities
- derived quantities
- professional quantities
- energy quantities
Ans : derived quantities
10. Which of the following statements about approximation is wrong?
- Approximation gives accurate value.
- Approximation simplifi es the calculation.
- Approximation is very useful when little information is available.
- Approximation gives the nearest value only.
Ans : Approximation gives accurate value.
II. Fill in the blanks.
- The solid angle is measured in _______. Ans : steradian
- _______ recognized the need of ‘Standard Units’ for physical quantities. Ans : International system of units
- The coldness or hotness of a substance is expressed by _______. Ans : temperature
- _______ is used to measure electric current. Ans : Ammeter
- _______ of substance, contains 6.023 × 10+23 atoms or molecules. Ans : One mole
- Luminous Intensity is the amount of visible light, that is emitted in unit area per unit _______. Ans : solldangle
- Quartz clock uses _______ oscillations. Ans : electronic
- The uncertainty in measurement is called as _______. Ans : errors
- _______ is the closeness of the measured value to the original value. Ans : Accuracy
- The intersection of two straight lines gives us_______. Ans : plane angle
III. True or False.
- SI units are metric system of units. Ans : True
- 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.
- 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.
- One coulomb of charge flowing per minute is called ‘ampere’. Ans : False
Cu. An. : One coulomb of charge flowing per second is called ‘ampere’
- Amount of substance gives the number of particles present in the substance. Ans : True
- Intensity of light from a candle is approximately equal to one ‘candela’. Ans : True
- 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’.
- Quartz clocks are used in GPS Devices. Ans : False
Cu. An. : Atomic clocks are used in GPS Devices.
- Candela is used to express electric field intensity. Ans : False
Cu. An. : Candelais used to express light intensity.
- The number 4.582 can be rounded off as 4.58. Ans : True
IV. Match the following:
- Temperature – Closeness to the Actual Value
- Plane Angle – Measure of hotness or coldness
- Solid Angle – Closeness to two or more measurements
- Accuracy – Angle formed by the intersection of three or more planes
- 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
- If both assertion and reason are true and reason is the correct explanation of the assertion.
- If both assertion and reason are true but reason is not the correct explanation of the assertion.
- Assertion is true, but reason is false.
- Assertion is false, but reason is true.
- 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.