chapter 2 physics measurement class 6 answers

 

Warm-up Activity

1. What is the pneumonic device for remembering the metric system?

   • The pneumonic device isn't directly mentioned in the text provided, but a common one is: King Henry Died By Drinking Chocolate Milk (Kilo, Hecto, Deca, Base, Deci, Centi, Milli).

2. Name three basic metric units of measurement.

   • Metre (m) for length

   • Kilogram (kg) for mass

   • Second (s) for time.

3. How would you measure the weight of the following objects in metric system?

   • (a) Pencil: Measured in grams (g) or kilograms (kg), using a balance.

   • (b) Liquid medicine: Measured in millilitres (ml), using a measuring cylinder or syringe.

   • (c) Car: Measured in kilograms (kg) or tonnes (t), using a weighbridge or platform scale.

   • (d) Ink drop: Measured in milligrams (mg) or microlitres (µl), with a precise digital balance for weight or micropipette for volume.

Assess Yourself

1. Name any four fundamental quantities.

   • Length

   • Mass

   • Time

   • Temperature.

2. Name two multiple and two sub-multiple units of time.
   Multiple units:

   • Hour (h)

   • Minute (min)

   Sub-multiple units:

   • Millisecond (ms)

   • Microsecond (µs)

   (hours and minutes are multiples of seconds; milliseconds and microseconds are sub-multiples.)

3. State three things in each of the following cases:

   (a) Instruments used for measuring distances:

   • Ruler

   • Measuring tape

   • Vernier caliper

   (b) Quantities which indicate distance:

   • Length

   • Displacement

   • Height

4. What is the standard unit of length?

   • Metre (m).

Activity (Non-standard Units)

Try this yourself as a practical experiment, but example answers/format:

1. Your palm in digits: e.g., 4 digits.

2. Your cubit in handspans: e.g., 2.5 handspans.

3. The length of a pencil in digits: e.g., 6 digits.

4. The length and width of this book in palms: e.g., length = 1.5 palms, width = 1 palm.

5. The width of a blackboard in cubits: e.g., 5 cubits.

6. The distance across the room in paces: e.g., 10 paces.

Think Zone

1. Which would be the best unit to measure the following?

   • (a) Height of your teacher's table: Centimetre (cm) or metre (m)

   • (b) Length of your classroom: Metre (m)

   • (c) Breadth of your school playground: Metre (m) or kilometre (km) for very large playgrounds.

2. Why is it useful to have units of various sizes for measuring different objects?

   • It is more convenient and accurate. For very large objects, such as the distance between cities, a large unit like kilometre avoids dealing with big numbers. For small objects, such as a wire's thickness, using millimetres produces practical, manageable numbers.

Conversions (from Activity B example)

1. What is the width of the desk in millimetres?

   • If width in centimetres is, say, 60 cm: $60\text{ cm}\times 10=600\text{ mm}$

2. What is your height in metres?

   • If your height is 150 cm: $150\text{ cm}÷100=1.5\text{ m}$

3. What is the length of this book in centimetres?

• If length in millimetres is 200 mm: $200\text{ mm}÷10=20\text{ cm}$

Evaluate Your Understanding – Solutions

I. Select the Correct Option

1. The SI unit of length is

   • (a) metre

2. Symbol for Celsius:

   • (a) °C

3. 10 mm is equal to

   • (a) 1 cm

4. The SI unit of mass is

   • (c) kilogram

5. Measurement makes your judgement more

   • (c) Accurate

6. The space occupied by an object is called its

   • (b) volume

7. Correct placement of a block along a scale:

   • (c)
     (Block's left edge aligned with zero mark on the scale.)

II. Assertion and Reasoning

1. (a) Both Assertion (A) and Reason (R) are true

2. (a) Both Assertion (A) and Reason (R) are true

3. (a) Both Assertion (A) and Reason (R) are true

4. (a) Both Assertion (A) and Reason (R) are true

5. (c) Assertion (A) is false but Reason (R) is true

III. Fill in the Blanks

1. tons

2. 100

3. pure ice

4. degree of hotness

5. 37°C

6. weight

7. 10,000

IV. True or False (with Corrections)

1. False: The commonly used unit of temperature is Celsius.

2. True

3. True

4. False: The standard unit of time is second.

5. False: Measuring cylinders are used to measure the volume of liquids.

V. Match the Following

Column A	Column B
1. Length of a farm	(d) Measuring tape
2. Thickness of a ball	(e) Measuring scale and blocks
3. Mass of an apple	(b) Common balance
4. Period of time for study	(a) Clock
5. Temperature of the body	(c) Thermometer
6. Surface of a leaf	(f) Graph paper

VI. Pick the Odd One Out

1. Scale (others are non-standard units)

2. Kilogram (others are units of length)

3. Sand clock (device, others are units of time)

4. Area (quantity, others are devices)

VII. One Word/One Statement Answers

1. Necessary to have standard units:
   To ensure uniformity and accuracy in measurements.

2. Examples:

   • (a) Instruments for distances: Ruler, measuring tape, vernier calliper

   • (b) Quantities for distance: Length, height, depth

   • (c) Units for wheat: Kilogram, quintal, tonne

   • (d) Device for gold/silver: Electronic balance (or digital balance)

VIII. Definitions

1. Mass: The quantity of matter present in a body.

2. Time: The interval between two events.

3. Measurement: Comparing an unknown quantity with a standard quantity.

4. Temperature: The degree of hotness or coldness of a body.

IX. Short Answer Questions

1. Hand-span and cubit:
   They are not standard because they vary from person to person.

2. Area and its SI unit:
   Area is the surface occupied by an object. SI unit is m².

3. Normal temperature and device:
   37°C (98.6°F), measured by a clinical thermometer.

4. Need for standard units:
   To avoid confusion and ensure uniform communication in measurements.

X. Detailed Questions

1. Finding sheet thickness:
   Stack a large number of sheets, measure total thickness, then divide by number of sheets.

2. Precautions with metre scale:

   • Place scale in contact with object.

   • Align eye perpendicularly.

   • Use intact ends for zero.

3. Measuring diameter of a ball:
   Place the ball between two blocks and measure the distance between the inner faces with a scale.

4. Thickness of a one-rupee coin:
   Stack 12 coins, measure total thickness, thickness = total/no. of coins.

5. Precautions for doctor’s thermometer:

   • Shake down before use

   • Place under tongue/armpit for 1–2 min

   • Read before mercury falls back

   • Clean after use

XI. Differentiate

	Beam Balance	Electronic Balance
Working	Manual weights, pointer	Electronic display, sensor
Accuracy	Less accurate	More accurate
Usage	Fruit seller, lab	Jeweller, lab

	Stopwatch	Stop clock
Precision	Fraction of seconds	Whole seconds
Use	Sports, labs	Older events, rough timing

	Doctor’s Thermometer	Laboratory Thermometer
Range	35–43°C (body)	-10°C to 100°C
Purpose	Body temperature	General lab temp
Feature	Constriction for mercury	No constriction

XII. Numericals

1. Thickness of one 5-rupee coin:
   Total = 3 cm 5 mm = 3.5 cm; 1 coin = 3.5/12 = 0.29 cm

2. Area of field:
   Length = 5500 cm, Breadth = 4000 cm
   Area = (5500 × 4000) cm² = 22,000,000 cm² = 2200 m²

3. Breadth calculation:
   Area = 450 cm², Length = 25 cm
   Breadth = 450/25 = 18 cm

4. Convert 17:30 to 12hr format:
   5:30 PM

5. Train time calculation:
   4:45 (AM) to 23:30 (PM) = 18 h 45 min

HOTS and Critical Thinking

1. Comparing Area of Square and Rectangle

   • Square box: Side = 6 m
     Area = $6\times 6=36{\text{m}}^2$

   • Rectangle box: Sides = 4 m × 9 m
     Area = $4\times 9=36{\text{m}}^2$

   • Which is bigger?
     Both have equal area: 36 m². By how much? 0 m² (no difference).

   • Suggest a rectangle with combined areas:
     Total area = $36+36=72{\text{m}}^2$.
     Example: A rectangle with sides 12 m × 6 m.

2. Govind Feeling Cold on a Hot Summer Day

   • Govind’s body temperature is likely below normal, as feeling cold despite hot weather suggests a drop in body temperature.

   • How will he know his temperature?
     He should use a clinical thermometer.

   • Steps to check:

     1. Sterilize and shake down the thermometer below 35°C.

     2. Place it under his tongue or armpit for 1–2 minutes.

     3. Remove and read the temperature.

     4. Clean the thermometer after use.

3. Stick and Eye Position – Parallax Error

   • Readings:

     • Eye at A: May see $>7.4\text{cm}$

     • Eye at B (center, directly above): Correct reading, e.g. 7.4 cm

     • Eye at C: May see $<7.4\text{cm}$

   • Are readings same? No, only the direct position (B) is correct.

   • Correct eye position: Eye must be perpendicularly above the mark.
     Correct length of the stick: 7.4 cm

4. Shikha’s Birthday Only Once Every 4 Years

   • Birthday: 29th February (“leap year day”)

   • Why not every year?
     February 29th occurs only in leap years (every 4 years).

5. Measuring Liquid Temperature in Lab with Thermometer

   • Steps:

     1. Place the laboratory thermometer in the beaker so the bulb is fully immersed (do not touch the walls or base).

     2. Wait until the mercury level becomes steady.

     3. Read the value at eye level (to avoid parallax error).

     4. Record the temperature.

6. Maya Measures Mass with Beam and Electronic Balance

   • Beam balance reading: 250 g

   • Electronic balance reading: 255 g

   • Reason for difference:

     • Electronic balance is more precise and sensitive.

     • Beam balance may have slight human error while adjusting weights, and may not be zeroed correctly.

Diagram-based Questions

1. Area of Shaded Portion:

   • (a) Rectangle 2 cm × 6 cm
     Area: $2\times 6=12{\text{cm}}^2$

   • (b) Square 4 cm × 4 cm
     Area: $4\times 4=16{\text{cm}}^2$

2. By Counting Squares:

   • (a) 18 squares = 18 cm²

   • (b) 43 squares = 43 cm²

Case-based / Passage-based Questions

1. Pendulum Time Measurement – Shalu’s Observations

   • Recorded times: Clock: 32 s, Watch: 31.5 s, Stopwatch: 31 s

   • (a) Accuracy and Precision:

     • Stopwatch: Most precise (records fractions of a second).

     • Watch: Less precise than stopwatch, more than clock.

     • Clock: Least precise for short intervals.

   • (b) Accuracy vs. Precision:

     • Accuracy: Closeness to true value.

     • Precision: Reproducibility of results; how close repeated measures are to each other.

   • (c) Convert 31.5 s to minutes:
     $31.5\text{s}=0.525\text{min}$

   • (d) Proper unit and symbol:

     • Time: second (s)

2. Peter Measures Pencil Length with Different Tools

   • Measurements: Ruler – 15 cm, Measuring tape – 14.5 cm

   • (a) Importance of correct tool:
     Use of appropriate tools ensures accuracy; small/rigid objects need rulers, flexible objects or longer lengths need tapes.

   • (b) Correct Usage:

     • Ruler: Align pencil with zero, keep ruler flat, read straight above.

     • Tape: Stretch straight without slack; align start with pencil’s end.

   • (c) Convert 14.5 cm to mm:
     $14.5\text{cm}\times 10=145\text{mm}$

   • (d) Proper unit and symbol:

     • Length: metre (m), commonly centimetre (cm) or millimetre (mm) for small objects.

Experiential Learning Questions

1. Finding Circumference of a Coin with Thread

   • Wrap a thread around the edge once, mark the endpoint, straighten and measure its length with a ruler – that’s the circumference.

2. Crossword Puzzle Clues:

   • Across:

     • 2. Kelvin

     • 3. Measurement

     • 4. Area

     • 6. Cubit

   • Down:

     • 1. Temperature

     • 5. Error

     • 7. Time

Project Ideas

• Measure and record your height and weight, then calculate the average for your class.

• Draw the outline of your palm on graph paper and count the squares to estimate the area.

• Collect and document various measuring devices, stating:

  • Name of quantity measured

  • Physical type of quantity (length, mass, etc.)

  • SI and CGS units used for each