Selina Concise Physics Class 8 ICSE Solutions – Physical Quantities and Measurement
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Selina Concise ICSE Solutions For class 8 Physics chapter 2 – Physical Quantities and Measurement
- MASS Is the quantity of matter contained in a body.
VOLUME is the space occupied by body.
- Equal mass of IRON and cotton, iron will have less volume than cotton.
- Equal volume of Iron and cotton, the mass of iron is more than mass of cotton, because iron denser than cotton.
- DENSITY “Is ratio of mass of substance to volume of substance”
D = M/V = KG/M3 The SI. unit of density is kg M-3
- Density of a substance does not change with change in shape or size.
- When a substance is heated it expands and volume increases. Hence density decreases.
Water has maximum density at 4°C i.e. density of water increases from 0°C to 4°C and decreases above 4°C.
- Volume of substance is measured by formula V = L × B × H or 4/3 or by measuring cylinder.
- Mass is measured by beam balance or spring balance.
- RELATIVE DENSITY of substance is the density compare with water i.e. How many times the substance is DENSER than water. Since density of water is 1 Gcm-3, so density of a substance in Gcm-3 = relative density of substance.
S.I. unit of R.D. > has no units — since it is the ratio of same
- If a substance has density more than liquid it SINKS in the liquid and if the density of substance is LESS than liquid it floats on liquid.
- BUOYANT FORCE “The force exerted by liquid acting vertically
upward on a body and is equal to the weight of liquid displaced by its immersed part.”
- Weight of body Acting vertically downward. This force has the tendency to sink the body.
- LAW OF FLOATATION “When a body floats in a liquid, the weight of the liquid displaced by its immersed part is equal to the total weight of the body.” While floating
wt. of floating body W=wt. of liquid displaced by its immersed part FB i.e. Apparent wt. of floating body is zero.
Density of body is greater than density of liquid. The body sinks.
Density of body is equal to the density of liquid. The body float where ever it is left in liquid.
Density of body is less than density of liquid. The body rises to the surface and floats.
A. Objective Questions
1. Write true or false for each statement
(a) Equal volumes of the two different substances have equal masses.
Equal volumes of the two different substances have different masses.
(b) The density of a piece of brass will change by changing its size or shape.
(c) The density of a liquid decreases with increase in its temperature.
(d) Relative density of water is 1.0.
(e) Relative density of a substance is expressed in g cm-3.
Relative density of a substance has no units.
(f) When a body is immersed in a liquid, the buoyant force experienced by the body is equal to the volume of the liquid displaced by it.
The buoyant force is equal to the weight of the liquid displaced by the immersed part of body.
(g) A body experiences the same buoyant force while floating in watr or alcohol.
(h) A body experiences the same buoyant force when it floats or sinks in water.
(i) A body floats in a liquid when its weight becomes equal to the weight of the liquid displaced by its submerged part. .
(j) A body while floating, sinks deeper in a liquid of low density than in a liquid of high density.
2. Fill in the blanks
(a) 1 kg is the mass of 1000 ml of water at 4°C.
(b) Mass = density x volume.
(c) The S.I. unit of density is Kg m-3
(d) Density of water is 1000 Kg m-3.
(e) 1 g cm-3 = 1000 Kg m-3.
(f) The density of a body which sinks in water is more than 1000 Kg m-3.
(g) Abody sinks in a liquid A, butt floats in a liquid B. The density of liquid A is less than the density of liquid B.
(h) A body X sinks in water, but a body Y floats on water. The density of the body X is more than the density of body Y.
(i) The buoyant force experienced by a body when floating in salt¬water is equal to or same that of when floating in pure water.
(j) The weight of a body floating in a liquid is zero.
3. Match the following
4. Select the correct alternative
(a) The correct relation is
- Density = Mass x Volume
- Mass = Density x Volume
- Volume = Density x Mass
- Density = Mass + Volume
(b) The relative density of alcohol is 0.8. Its density is
- 800 kg nr3
- 800 g cm-3
- 0.8 kg m-3
(c) A block of wood of density 0.8 g cm-3 has a volume of 60 cm3. The mass of block is
- 60.8 g
- 75 g
- 48 g
- 0.013 g
(d) The density of aluminium is 2.7 g cm-3 and that of brass 8.4 g cm’3. The correct statement is
- Equal masses of aluminium and brass have equal volumes
- The mass of a certain volume of brass is more than the mass of equal volume of aluminium.
- The volume of a certain mass of brass is more than the volume of equal mass of aluminium.
- Equal volumes of aluminium and brass have equal masses.
(e) A density bottle has a marking 25 mL on it. It means that:
- the mass of density bottle is 25 g
- the density bottle will store 25 ml of any liquid in it
- the density bottle will store 25 ml of water, but more volume of liquid denser than water.
- the density bottle will store 25 ml of water, but more volume of a liquid lighter than water.
(f) The correct statement is
- The buoyant force on a body is equal to the volume of the liquid displaced by it ‘
- The buoyant force on a body is equal to the volume of the body
- The buoyant force on a body is equal to the weight of the liquid displaced by it
- The buoyant force on a body is always equal to the weight of the body.
(g) A piece of wood floats on water. The buoyant force on wood will be
- more than the weight of the wood piece
- equal to the weight of the wood piece
- less than the weight of the wood piece.
(h) The weight of a body is more than the buoyant force experienced by it, due to a liquid. The body will
- float with its some part outside the liquid
- float just below the surface of liquid
- float with whole of its volume above the surface of liquid.