# __Class -6 Physics Chapter2- Measurement__

__Class -6 Physics Chapter2- Measurement__

__Short-Answer Questions__

__Short-Answer Questions__

**Q1. What is meant by the unit of physical quantity?**

**Ans:** A unit is a known measure of a physical quantity with which physical quantities of the same kind are compared.

**Q2. Give two examples showing how the magnitude of a physical quantity is expressed as a number and a unit?**

**Ans**: examples-1) 5.45 m- 5.4 5 is magnitude of physical quantity length and metre is a unit

2) 10 kg- 10 is magnitude of physical quantity and kg is a unit.

**Q3. What is length ? What is its unit in CGS and the FPS system?**

**Ans: Length is the distance between two points. **

**Its CGS unit is cm and FPS unit is foot.**

**Q4. Mention two advantages of a metric system?**

**Ans:** Two advantages of metric system-

1) A single unit is defined for each physical quantity such as length and mass.

2) larger smaller forms of a unit are related to each other by powers of 10.

**Q5. How many units are defined in S.I ? Give the SI units of three basic quantities?**

**Ans:** SI system defines the units of seven quantities called base quantities or fundamental quantities.

S.I Units of three base quantities

i) Length - metre

ii) Mass - kilogram

iii) Time - second

**Q6. What is mass ? Mention three units of mass.**

**Ans:** mass is the amount of matter content in a body . Three units of mass -

SI unit kilogram

FPS unit pound

CGS unit gram.

**Q7. Distinguish between time shown by clock and a time interval give an example of each?**

**Ans: **A time clock is a simple reading of time that can be broken down into hours, minutes and seconds etc. Whereas, time interval is the time between two or events.

Example, time shown by a clock is school starts at 7.30 am

Example, the time interval - duration of one period - 40 mins.

**Q8. Mention two scales of temperature used in everyday life . Give example**

**Ans:** the Celsius and Fahrenheit scales are to scales of temperature used in everyday life.

**Q 9. What are the lower and upper fix points of the Celsius scale?**

**Ans:** Celsius scale low fixed point is zero degree centigrade and up of 100 degree centigrade.

**Q 10. Why does a clinic thermometer have a kink ?**

**Ans: **The kink in clinical thermometer does not allow the mercury to move back into the bulb by itself.

**Q 11. Why is it not necessary to write A.M. or P.M. in the 24 hour clock system?**

**Ans:** In the 24 hour clock system , time is always denoted by four digits. 00.00 to 11.59 denote AM and 12.00 to 23.59 denote PM. It is thus not required to write A.M and PM in this system.

**Q 12. Mention one advantage and one disadvantage of approximation?**

**Ans:** One advantage of approximation is it safes time and saves us that trouble of measuring. Disadvantage is it is inaccurate.

**Q13. How do you find the average of a number of values?**

**Ans: **This is the arithmetic mean, and is calculated by adding a group of numbers and then dividing by the count of those numbers. For example, the average of 2, 3, 3, 5, 7, and 10 is

Average =( 2+3+3+5+7+10) / 6= 30/6=5

**Q14. How would you identify your standard metre scale.**

**Ans:** A standard metre has the arrow marks and the stamp.

**Q 15. Mention the defects which may be present in a beam balance used in the market?**

**Ans:** Balances may have following two defects-1. The two arms of the beam may be unequal.

2. The pans may be unequal in weight

**:**

__Long-Answer Questions__**Q1. Describe the precautions required while measuring length.**

**Ans:** The following precautions required while measuring length-

1. Avoid using the ends of the scales.

2.Place the scale parallel to the length of the object

**Q2. Describe how would you measure a) the diameter of a table tennis ball and b) the radius of a thin wire**

**Ans:** __Measuring the diameter of a tennis ball-__1. Place the ball between two blocks.

2. Place a scale against the blocks.

3. Read the position of the inner edge of each block on the scale.

4. The difference between the reading is equal to the diameter of the tennis ball

__Measuring the radius of a wire__-

1. Wind about 30 to 40 turns of a wire around a pencil. The turns of the wire should touch each other.

2. Measure the combined thickness of all the turns with the help of a scale . Divide the measured length by the number of turns to get the thickness of a wire.

**Q3. Name three instruments used for measuring mass. Mention three defect that balance may have?**

**Ans:**The three instruments used for measuring mass are-1 simple Beam Balance. 2. A jeweller's balance 3. An electronic weighing machine

Balances may have following three defects-1. The beam may be fixed rigidly to the handle used to suspend the balance.

2.The two arms of the beam may be unequal.

3. The pans may be unequal in weight.

**Q4. Describe the construction of a laboratory thermometer**

**Ans:** .The thermometer used in laboratories is called laboratory thermometer .It has a small bulb at one end of a long glass cylinder called the stem. The bulb holds mercury (a silvery metal) and is connected to a very thin tube inside the stem called the bore. When the bulb is heated, the mercury expands into the bore (things expand when they are heated). It looks like a thin, shining thread. A temperature scale is marked on the stem. The thermometer reading is the temperature mark at the end of the thread of mercury.

__Objective questions__:__Choose the correct option__*:*

**1. The magnitude of a physical quantity consists of**

a) **A number and a unit**

b) a number

(c) a unit

(d)** **a unit and its symbol

**2. The S.I. unit of length is the**

(a) millimetre

(b) centimetre

(c) **metre **

(d) kilometre

**3. Which of the following represents the magnitude of a temperature correctly ?**

(a) 10 k

(b) 10 Kelvins

(c)** **10 Ks

(d**) 10 K**

**4. The error in measurement caused by positioning the eye incorrectly is called**

(a) parallel error

(b)** **standard error** **

(c) eye error

(d) **parallax error**

**5. Which of the following is not true of the standard weights satisfied by the department of weights and measures?**

(a) Larger weights are made of iron

(b) **smaller weights are made of lead**

(c) the value written on the top

(d) they are either hexagonal or circular in shape.

**6. Which of the following is a time interval**

(a) The time when you wake up

(b) **The time you take for your bath**

(c) The time when school gets over

(d) The time when you go to bed.

**7. Stop watches and stop clocks are used**

(a) as 24 - hour clocks

(b) as 12 - hour clocks

(c) **for accurate measurement of time intervals**

(d) for finding average time

**:**

__Fill in the blanks__(1) Measurementis basically a process of ** comparison**.

(2) A unit is so chosen that the numerical value of a measurement is as **Simple** as possible.

(3) The fps unit of Mass is the __pound__

(4) The correct symbol for kilometres is __km__

(5) The prefix 'milli'- denotes the factor __10-³__

(6) Mass is the amount of ** matter** contained in a body.

(7) 1 metric ton = ** 1000 kg**.

(8) The steam point is used the upper fixed point on the Celsius scale.

(9) Laboratory thermometers have a range of ** -10⁰C **to 110⁰C .

(10) A railway ticket mentions the time of departure as 19:20 , which is** 7: 20 **PM.

**:**

__Write true or false__1. When we use a symbol of unit named after a person we use small letters-False

2. The range of clinical thermometer is 35 degree centigrade to 43 degree centigrade. - True

3. At a grocer's shop all commodities are sold by weight- True

4. The unit we used to measure the physical quantity is a matter of choice. - True

5. A simple balance can be measure small masses accurately. - False

6. Usually, while cooking , we add salt by approximation. - True

7. An average gives us an idea of the largest value in a group of numbers. - False

Numericals

**Q 1. Express the length 10 cm in metre**

Ans: 10cm =0.1 m

Q2.

**The masses of 5 old cricket balls are 195 gram 198 gram 205 gram 202 gram 203 gram . Find the average mass of the balls?**

Ans: Average = (195+198+205+202+203 )/5

= 200.6 gram

Q3.

**A string is own around a pencil 50 times the total length of all the terms is 5 cm find the thickness of the same**?

Ans: Thickness of wire = Total length / no. Of turns

= 5 cm / 50 = 0.1 cm= 1 mm

Q4.

**The clock at a railway platform reach 23 :47 when a train arrived and 00:08 when it left. How long did the train stop at the station ? The next train arrived at 01:05. What was the time interval between the departure of the first train and the arrival of second train ?**

Ans: The stoppage time of first train = 21 minutes.

Time duration between between the departure of the first train and the arrival of second train = 01:05 - 00:08= 57 minutes.

Q5.

**The area of a piece of land 1800 ft². Find this in metre square?**

Ans: 1 m² = 10.76 ft²

1 ft²=( 1/ 10.76 ) m²

1800 ft² = (1800 x 1/ 10.76) m²

= 167.29 m²

Q6.

**The mass of a cricket ball is 198 g Express this in pounds.**

Ans: 1pound = 453.6 g

1 g = ( 1/ 453.6) pound

198 g = 198 x ( 1/ 453.6) pounds = 0.436 pound

Q7.

**The height of a building is 12.36 m Express this in feet?**

Ans 1m = 3.28 ft

12.36 m = 12.36 x 3.28 ft= 40.54 ft

Q8.

**The average height of a student in a class is 5.2 ft .Express this in centimetre**