Physical Quantities and Measurement

It starts by explaining that physical quantities are measurable aspects of the physical world, like length, mass, time, temperature, and area.

The chapter then emphasizes the importance of units in measurement. It likely introduces the International System of Units (SI), which is the standard system used globally. Common SI units like meter (m) for length, kilogram (kg) for mass, second (s) for time, and degree Celsius (°C) for temperature would be discussed.

You’d learn about the need for standard units to ensure uniformity and accuracy in measurements across different places and times. The chapter would probably explain that a measurement consists of a numerical value and a unit.

The chapter would also cover different measuring instruments used for various physical quantities. For example:

• Length: Ruler, measuring tape
• Mass: Common balance, beam balance
• Time: Clock, stopwatch
• Area: Understanding how to calculate the area of regular shapes (like squares and rectangles) using length measurements.

Finally, the chapter likely touches upon the importance of accuracy and avoiding common errors in measurement. This might include understanding the concept of least count of a measuring instrument and practicing careful observation while taking readings.

In essence, this chapter lays the groundwork for understanding how we quantify the world around us using standard units and appropriate tools, while also emphasizing the need for careful measurement techniques.

2. Fill in the blanks

(a) The S.I. unit of length is ——–of time is ———of mass is ——.

Ans : Metre , Second , Kilogram
(b) °C is the unit of ———-.

Ans : Temperature

(c) 1 metric tonne = ——–

Ans : 1000 kg

(d) The zero mark in Celsius thermometer is the melting point of ——-

Ans : Ice
(e) The thermometer used to measure the human body temperature is called the ———thermometer.

Ans : Clinical
(f) The normal temperature of the human body is ——-°C or——– °F.

Ans : 37 , 98.6

(g) The ——–of an object is measured with the help of a beam balance.

Ans : Mass

3. Match the following columns

4. Select the correct alternative

(a) The symbol of degree celsius is

1. °C
2.  °F
3.  K
4.  °K

Ans:°C

(b) lO mm is equal to

1.  1cm
2.  1m
3.  10dm
4.  10cm

Ans: 1cm

(c) The amount of surface occupied by an object is called its:

1.  volume
2.  area
3.  mass
4.  length

Ans:  area

(d) A metre ruler is graduated in:

1.  m
2.  cm
3.  mm
4.  km

Ans:   mm

(e) A thermometre is graduated in:

1.  kelvin
2.  °C
3.  g
4.  cm

Ans:   °C

B. Short/Long Answer Questions

1)What is measurement ? How is a measurement expressed ?
Answer:Measurement is essentially the act of comparing an unknown quantity with a known standard quantity of the same kind. It’s how we assign numerical values to physical attributes of objects or events.  

1. A numerical value (magnitude): This indicates how many times the standard unit is contained within the measured quantity.  

2. A unit: This specifies the standard quantity used for the comparison (e.g., meters for length, kilograms for mass, seconds for time).  

2)State two characteristics of a unit.

Answer:

First, it needs to be well-defined. This means it should have a clear and consistent meaning so that anyone, anywhere, can understand exactly what it refers to.

Second, a good unit should be easily reproducible. This means it should be possible to create or obtain a standard representation of the unit without too much difficulty.

 3)Name four basic measurements in our daily life.

Answer:Time: Checking the clock to know when to wake up, go to school, or meet friends.

Length/Distance: Figuring out how far away something is, like the distance to the market or how tall you are.

Mass/Weight: Knowing how much groceries to buy or checking your own weight.

Temperature: Deciding what clothes to wear based on how hot or cold it is outside.

4)What are the S.I. units of

1.  mass
2.  length
3.  time and
4.  temperature.

Answer: Write their names and symbols

5)Define one metre, the S.I. unit of length. State its one multiple and one sub multiple.

Ans :

One metre is the base unit of length in the SI system. It’s currently defined very precisely as the length of the path that light travels in a vacuum in a tiny fraction of a second (specifically, 1/299,792,458 of a second).

The metre (m) is the SI base unit of length. It is defined as:  

“The length of the path travelled by light in vacuum during a time interval of 1/299,792,458 of a second.”

This definition, adopted in 1983, is based on the fundamental constant, the speed of light in a vacuum (c). This makes the definition very precise and universally reproducible.  

One Multiple and One Sub-Multiple of a Metre:

• One Multiple:Kilometre (km)
  • 1 kilometre = 1000 metres = 103 m  
• One Sub-Multiple:Centimetre (cm)
  • 1 centimetre = 0.01 metres = 10−2 m

 6)Convert the following quantities as indicated

(a) 12 inch = ft

(b) 1 ft = cm

(c) 20 cm = m

(d) 4.2 m = cm

(e) 0.2 km = m

(f) 0.2 cm = mm

(g) 1 yard = m

Answer:

7)(a) Describe in steps how you would measure the length of a pencil using a metre rule. Draw a diagram if necessary.

Answer:Place the pencil: Lay the pencil straight along the metre rule. Make sure one end of the pencil is exactly at the zero mark (the starting point) of the rule.
Look straight down: Position your eye directly above the point where the other end of the pencil reaches the metre rule. This helps you avoid parallax error (where the reading looks different if you look at it from an angle).
Read the mark: Note the reading on the metre rule where the other end of the pencil lines up. This reading gives you the length of the pencil in centimetres or metres, depending on the markings on your rule. You might need to estimate if the end falls between two small markings for a more precise measurement.

 8)Name the device which you will use to measure the perimeter of your playground. Describe in steps how you will use it.

Answer:measure the perimeter of my playground, I would use a measuring tape.

Here’s how I would do it step-by-step:

1. Start at one corner: I’d pick a starting point on one of the corners of the playground and place the zero mark of the measuring tape firmly on that spot.
2. Measure along the edge: I would then carefully stretch the measuring tape along one straight edge of the playground, making sure it follows the boundary closely and doesn’t sag or go off course.
3. Mark the end: Once I reach the next corner, I would note down the measurement shown on the tape at that point.
4. Repeat for all sides: I would then lift the tape, place its zero mark on the corner I just reached, and measure along the next straight edge. I would repeat this process for all the sides of the playground.
5. Add up the measurements: Finally, I would add together all the individual measurements I recorded for each side. The total sum would give me the perimeter of the playground.

9)The diagram below shows a stick placed along a metre RULER. The length of the stick is measured keeping the eye at positions A, B and C.

Answer: I see the diagram. It shows a stick (PQ) placed along a ruler marked in centimeters. There are three eye positions labeled A, B, and C, each looking at the ruler to take a reading of the stick’s length. The readings taken from each position are also indicated:

• From position A, the reading appears to be 3.4 cm.
• From position B, the reading appears to be 3.2 cm.
• From position C, the reading appears to be 3.0 cm.

10) Define mass. State its (1) S.I. (2) C.GS and (3) EP.S. units. How are they related ?

Answer:

Mass is a fundamental property of an object that represents the amount of “stuff” it’s made of. You can think of it as a measure of how much matter is contained within the object. It’s also a measure of an object’s resistance to changes in its state of motion (inertia).  

Here are the units of mass in different systems:

1. S.I. Unit: The standard international unit of mass is the kilogram (kg).  
2. C.G.S. Unit: In the Centimetre-Gram-Second system, the unit of mass is the gram (g).  
3. F.P.S. Unit: In the Foot-Pound-Second system, the unit of mass is the pound-mass (lbm). (Sometimes, the slug is used as the unit of mass in the FPS system, but pound-mass is more common in everyday use.)
   

Here’s how these units are related:

• 1 kilogram (kg) = 1000 grams (g)  
• 1 kilogram (kg) ≈ 2.20462 pound-mass (lbm)
• 1 pound-mass (lbm) ≈ 0.453592 kilograms (kg)

11) Convert the following quantities as indicated:

(a) 2500 kg = ………. metric tonne.

(b) 150 kg = quintal

(e) 10 lb = ………. kg

(d) 250 g = … .kg

(e) 0.01 kg = ………. g

(f) 5 mg = ………. Kg

Ans : 

12) Name the instrument which is commonly used to measure the mass of a body. State how is it used ?

Answer:

Here’s how it’s generally used:

Place the object: The body whose mass you want to find is placed on one side of the balance, usually on a pan or platform.   

Add standard masses: Standardized masses (also known as weights) are then added to the other side of the balance, also typically on a pan.

Achieve balance: You keep adding or adjusting the standard masses until the balance is level or reaches a state of equilibrium.

Read the total mass: The total mass of the body is then determined by adding up the values of all the standard masses that were needed to achieve balance.

Different types of balances, like beam balances or electronic balances, might have slight variations in their operation, but the fundamental principle of comparing the unknown mass with known standard masses remains the same.

13)Define one kilogram, the S.I. unit of mass. How is it related to (i) quintal (ii) metric tonne and (iii) gram.

Answer:

One kilogram is the base unit of mass in the International System of Units (SI). It’s currently defined by the mass of a specific object, the international prototype of the kilogram, which is made of platinum and iridium and kept under very special conditions.  

Here’s how a kilogram relates to the other units you asked about:

(i) Quintal: One quintal is equal to 100 kilograms.  

(ii) Metric tonne: One metric tonne is equal to 1000 kilograms.  

(iii) Gram: One kilogram is equal to 1000 grams

14) Name and define the S.I. unit of time. How is it related to (i) minute (ii) hour, (iii) day and (iv) year ?

Answer:

The SI unit of time is the second. It’s defined very precisely using atomic clocks, but you can think of it as a very short, specific duration.  

Here’s how the second is related to other time units:

(i) Minute: 1 minute = 60 seconds  

(ii) Hour: 1 hour = 60 minutes = 3600 seconds  

(iii) Day: 1 day = 24 hours = 1440 minutes = 86400 seconds

(iv) Year: 1 year = 365 days (in a regular year

15)Name two devices used to measure the short time interval of an event.

Answer:

A stopwatch is designed specifically for timing events and can be started and stopped precisely to measure the duration.  

A stopwatch is another device for measuring time intervals, often found built into devices like laboratory timers or even some wristwatches. Like a stopwatch, it can be started and stopped to record how long an event lasts.

16) Express in second

1.  3 minute 15 second and
2.  5 hour 2 minute 5 second.

Answer:

1)3 minutes 15 seconds: First, we know that 1 minute has 60 seconds. So, 3 minutes would be 3×60=180 seconds. Now, we just need to add the extra 15 seconds: 180 seconds+15 seconds=195 seconds.
2)5 hours 2 minutes 5 seconds: Let’s break this down step by step. First, convert the hours to minutes: 1 hour has 60 minutes, so 5 hours would be 5×60=300 minutes. Next, add the existing 2 minutes: 300 minutes+2 minutes=302 minutes. Finally, add the remaining 5 seconds: 18120 seconds+5 seconds=18125 seconds. Therefore, 5 hours 2 minutes 5 seconds is equal to 18125 seconds.

17) What does the temperature measure ?

Answer:

Think of it as a way to quantify how much the particles within something are moving. Conversely, slower movement indicates a cooler temperature. So, temperature essentially tells us about the average kinetic energy of the particles in a substance

18) Name the

1.  S.I. unit and
2.  one common unit of temperature. Write their symbols also.

Answer:

The SI unit of temperature is the kelvin. Its symbol is K.  

A common unit of temperature is the degree Celsius. Its symbol is °C

19) Name the instrument used for measuring the temperature of a person. Draw its labelled neat diagram.

Answer:

The instrument used for measuring the temperature of a person is called a clinical thermometer.  

Explanation of the parts:

• Glass Stem: This is the long, narrow glass tube that contains mercury. It has markings (calibrations) to indicate the temperature, usually in degrees Celsius (°C) and sometimes in degrees Fahrenheit (°F).  
• Bulb containing Mercury: It contains mercury, which expands or contracts with changes in temperature.  
• Narrow Constriction (Kink): This is a very important, narrow part in the glass tube just above the bulb. This allows time to read the temperature accurately.  

How it works (briefly): When the bulb is placed in contact with a warm body, the mercury inside absorbs the heat and expands, moving up the glass stem. The narrow constriction traps the mercury at its highest point, indicating the body temperature even after the thermometer is removed.

20) Write the temperature of (i) melting ice (ii) boiling water.

Answer:

i) The temperature of melting ice is 0∘C​ or 32∘F​.  

(ii) The temperature of boiling water at standard atmospheric pressure is 100∘C​ or 212∘F​.

21) What is a clinical thermometer ? State its special feature. Draw a labelled neat diagram of a clinical thermometer showing the range of temperature marked on it.

Answer:

A special feature of a clinical thermometer is the kink (or constriction) in the glass tube just above the bulb. This narrow part prevents the mercury from falling back into the bulb quickly when the thermometer is removed from the body. This allows enough time to read the temperature accurately.The typical temperature range marked on a clinical thermometer is 35°C to 42°C (or 94°F to 108°F), which covers the normal range of human body temperatures and slight fevers.

22) What is the normal temperature of the human body ? How is it indicated in a clinical thermometer ?

Answer:

The normal temperature of the human body is generally around 37∘C​ or 98.6∘F​. However, this can vary slightly depending on the person, their activity level, and the time of day.  

In a clinical thermometer, the temperature is indicated by the level of a liquid, traditionally mercury but now often alcohol or another colored liquid, inside a narrow glass tube. The tube has markings along its side representing degrees in Celsius (°C) or Fahrenheit (°F), or sometimes both. The reading is taken at the point where the top of the liquid column stops, indicating the body temperature on the calibrated scale..

23) Can a clinical thermometer be used to measure the temperature of the boiling water ? Give reason for your answer.

Answer:

No, a clinical thermometer cannot be used to measure the temperature of boiling water because it is designed to measure body temperature only, which ranges from 35°C to 42°C. Boiling water is 100°C, which can damage the thermometer.

 24) Explain the term ‘area of a surface’.

Answer:

The ‘area of a surface’ tells us the amount of space a flat or curved surface covers. Think of it like measuring how much paint you’d need to cover a wall or how much fabric is in a piece of cloth. Essentially, it quantifies the extent of a surface

25) Name the S.I. unit of area and define it.

Answer:

The S.I. unit of area is the square meter​ (symbol: m2​).  

It’s the area enclosed by a square with sides that are each one meter long

26) How are the units

1.  square yard
2.  hectare
3. km2
4. cm2
5. mm2 related to the S.I. unit of area ?

Answer:

The SI unit of area is the square meter (m2). Here’s how the other units relate to it:  

• Square yard (yd2): 1 square yard is approximately equal to 0.836 m2​.  

• Hectare (ha): 1 hectare is exactly equal to 10,000 m2​.
• Square kilometer (km2): 1 square kilometer is exactly equal to 1,000,000 m2​ (or 106 m2).  

• Square centimeter (cm2): 1 square centimeter is exactly equal to 0.0001 m2​ (or 10−4 m2).
• Square millimeter (mm2): 1 square millimeter is exactly equal to 0.000001 m2​ (or 10−6 m2).

27) Explain how you will measure the area of (i) a square (b) a leaf?

Answer: 

measure the area of:

(i) A Square:

A square has four equal sides. Here’s how to find its area:

1. Measure one side: Use a ruler or measuring tape to measure the length of any one side of the square. Let’s say the length is ‘s’.
2. Calculate the area: The area of a square is found by multiplying the length of one side by itself. So, the area = s * s, or s².
3. State the unit: If the side was measured in centimeters (cm), the area would be in square centimeters (cm²). If it was in meters (m), the area would be in square meters (m²), and so on.

(b) A Leaf:

A leaf has an irregular shape, so we can’t use a simple formula. Here’s one way to estimate its area:

1. Trace the leaf: Place the leaf on a piece of graph paper (paper with small squares of known area, like 1 cm x 1 cm). Carefully trace the outline of the leaf on the graph paper.
2. Count the squares:
   • Count the number of full squares that are completely inside the traced outline.
   • Count the number of squares that are partially inside the outline. For the partial squares, you can estimate. A common method is to count any square that is more than half inside the outline as a full square, and ignore the rest.
3. Calculate the total area:
   • Let’s say ‘F’ is the number of full squares, and ‘P’ is the number of partially filled squares you’ve counted as full.
   • If each square on the graph paper has an area of 1 cm², then the approximate area of the leaf is (F + P) cm².
   • If the graph paper squares are a different size, you’ll need to multiply your count by the area of each individual square.