**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?

- 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

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.*

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

- 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.

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 **: 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?

6.023×10^{23}

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 6.023×10^{23} 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.