Physical Quantities and Measurement Class-8th Goyal Brothers Physics Solutions Chapter-2. We Provide Step by Step Answers of Objective, True False , Fill in the blanks, Match the following , Short/Long Answer Type of Chapter-2 Physical quantities and measurement Visit official Website  for detail information about ICSE Board Class-8.

## Physical Quantities and Measurement Class-8th

Goyal Brothers Physics Solutions Ch-2

 Board ICSE Class 8th Subject Physics Book Name Goyal Brothers Theme-2 Physical Quantities and Measurement Unit-1 Measurement of density, flotation and sinking Topic Solution of exercise questions Session 2023-24

### OBJECTIVE TYPE QUESTIONS

#### A. Fill in the blanks :

1. The density of zinc is 4.2gcm-3 . The volume of 420g of zinc is _100_ cm
2. An iron needle sinks in water as its density is _more_ than 1 gcm-3.
3. A solid ‘S’ floats in liquid ‘L’. The density of ‘S’ is _less_ than liquid ‘L’.
4. The density of milk is 1.04 gcm-3 Therefore, 1 cm3 of milk has a _mass_ of 1.04 g.
5. Sea breeze blows from the _sea_ towards the earth.

#### 1. Weight per unit volume of a substance is called density.

Correct Statement: Mass per unit volume of a substance is called density.

#### 2. More is the density of a liquid than a solid, more the volume of solid will submerge in it.

Correct Statement: Less is the density of a liquid than a solid, more the volume of solid will submerge in it.

#### 4.Land breeze flows from the sea toward the land

Correct Statement: Sea breeze flows from the sea toward the land

#### 5. With the rise in temperature of air its density increases.

Correct Statement: With the rise in temperature of air its density decreases.

#### C. Write ‘True’ or ‘False’ for the following statements :

1.A body having density of more than 1 gcm-3 sinks in water. [T]

2. The hot air rises up as its density increases.[F]

3.Liquids have density due to their molecules are tightly packed in a small volume. [T]

4.The sea breeze in the coastal region blows at night. [F]

5.The hot air in the rooms rises up and flows out of ventilators. The fresh and cold air from outside flows into room from doors and windows. [T]

#### 1. The density of mercury is 13.6 gcm-3 in CGS system. Its density in SI system is :

(a) 136 Kgm-3

(b)1360 Kgm-3

(c)13600 Kgm-3

(d) no change in density

Ans: (c)13600 Kgm-3

#### 2. When a liquid is heated, it expands and its level :

(a) rises upward

(b)Moves downward

(c) Remains same

(d)None of these

Ans: (a) rises upward

#### 3. In order to find the density of a solid we have to find its  :

(a) mass and area  7

(b) weight and volume

(c) weight and area

(d) mass and volume

Ans: (d) mass and volume

#### 4. When the air cools, its density :

(a) increases

(b) decreases

(c) does not change

(d) none of these

Ans: (b) decreases

#### 5. In coastal regions the density of air above sea, during night is :

(a) more than that of land air

(b) lass than that of land air

(c) same as that of land air

(d) none of these

Ans: (b) lass than that of land air

#### 5. Land breeze

 Column A Column B 1. The tiny glass bottle used for finding the density of a liquid. 4. Density bottle 2. Lines marked on the hull of merchant ships. 3. Plimsoll lines 3.A wind blowing in coastal regions during night. 5. Land breeze 4. The mass per unit volume. 1. Density 5. The density of freshwater in SI system. 2. 1000 Kgm-3

### STUDY QUESTIONS

#### Question 1. You are provided with a glass stopper and a measuring cylinder. How will you proceed to find the density of stopper ? Diagrams not required.

Answer: You have to insert the glass stopper in the measuring cylinder then mark and record. Then subtract the initial volume of water from that of the water and the glass stopper to get the volume of the stopper

#### Question 2. Briefly describe how will you find experimentally, density of kerosene oil with a density bottle.

Answer: You have to find the mass of an empty density bottle. After that, fill the bottle with water and weigh the bottle once again. Now repeat the same with kerosene. Now, divide the mass of the kerosene by mass of the water and you will get the density of kerosene.

#### Question 3. How does the density of a liquid change with the rise in temperature ?

Answer: On cooling a substance like liquid causes molecules to slow down and get slightly closer together, occupying a smaller volume that results in an increase in density. Therefore, with rise in temperature, the density decreases.

#### Question 4. On the basis of change of density with the change in temperature, explain how do the liquids get heated up, when heated in a vessel.

Answer: When a liquid is heated in a vessel then first of all vessel is heated and it expands slightly because expansion of solids is less than liquid. Now liquid is heated and it expands more than solids. This expansion in solids and liquids is due to the increase in molecular vibration because of the heat energy which causes an increase in volume and decrease in density. If you still go on heating the liquid then due to vigorous molecular motions, separation in the molecules further increases and they are converted in to gaseous state which increases the volume and decreases the density.

#### (a) How does the density of gases change with the rise in temperature ?

Answer: There is a decrease in density of a gas when increase in the temperature because the intermolecular space between the gas molecules is increased as a result volume increases and density decreases.

#### (b) What is the importance of above phenomenon in the formation of weather?

Answer: Due to the above phenomenon, the wind speed increases and low-pressure & high-pressure are created. This leads to change in weather.

#### Question 6. How is land breeze formed ? Explain.

Answer: During night, the land gets cooled down quicker as compared to the sea. The air above the sea is thus hotter than the air above the land. This air rises up and is replaced from the relatively cooler air from the land in the form of Land breeze.

#### Question 7. How is sea breeze formed ? Explain.

Answer: The warm air expands due to lesser density, decreasing the pressure over the land near the coast. In comparison to the air above the land, the air above the sea has a relatively higher pressure, causing air to flow from the high pressure towards the lower pressure resulting in a sea breeze.

#### Question 8. Two solids A and B of density 2.5 gm-3 and 0.80 gm-3 are placed in a liquid L of density 1.2 gm-3. Which solid is likely to float and why?

Answer: Solid B will float because its density is lower than the density of the liquid L.

#### Question 9. Why do objects like metals or stones sink in water ?

Answer: Objects like metals or stones sink in water due to the fact that the density of metal or stone is more than the density of water, and hence it sinks.

#### Question 10. Why do objects made of wood or plastic float in water ?

Answer: If an object is more dense than water it will sink when placed in water, and if it is less dense than water it will float. Therefore wood and plastic floats on water as they have very es density.

#### Question 11. Why an iron needle sinks in water but the iron ship floats in water ?

Answer: The weight of the water displaced by the ship is equal to its weight, so it floats. Whereas the weight of the water displaced by the iron nail is less than its weight so the iron nail sinks.

#### Question 12. Describe comparison of densities in the three states of matter.

Answer: The same number of particles in a gas spread further apart than in the liquid or solid states, thus the density is higher in case of solid than that of in the liquid and the least is in the gas. Increasing order of density of three states of matters is as follows: Gas < Liquid < Solid.

#### Question 13. A piece of wood of mass 150 g has a volume of 200 cm3 . Find the density of wood in

(a) CGS System

(b) SI System

Mass of wood (M) = 150 g
Volume of wood (V) = 200 Cm3
Density (D) =?

D = MV/MV

=150/200

=0.75 gcm-3

In S.I. system = 0.75 × 1000

= 750 kg m-3

(a) CGS System

(b) SI System

#### Question 15. Calculate the volume of wood of mass 6000 kg, when density of wood is 0.8 gm-3.

Volume of wood (V) = ?
Mass of wood (M) = 6000 kg
Density of wood D = 0.8 g/ Cm3
D=O.8g/Cm3=o=0.8 × I000 = 800kg /m3

D= M/V

V= M/D

=6000\800

=7.5m3

#### Question 17. An empty density bottle weighs 22 g. When filled completely with water, it weighs 50 g. When filled completely with brine solution , it weighs 54 g. calculate:

(a) volume of density bottle

(b) density of brine solution