Chapter 2 Physical quantities and measurement short notes with exercises

Objective Questions

Question 1

Write true or false for each statement:

(a) Equal volumes of two different substances have equal masses.

(b) The density of a piece of brass will change by changing its size or shape.

(d) Relative density of water is 1.0.

(e) Relative density of a substance is expressed in g cm^-3.

(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.

(g) A body experiences the same buoyant force while floating in water 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.

Answer

(a) False
Correct Statement — Equal volumes of two different substances have different masses.

(b) False
Correct Statement — The density of a piece of brass will not change by changing its size or shape.

(d) True

(e) False
Correct Statement — Relative density has no unit.

(f) False
Correct Statement — When a body is immersed in a liquid, the buoyant force experienced by the body is equal to the weight of the liquid displaced by the immersed part of the body.

(g) True

(h) False
Correct Statement — The buoyant force experience by the body is different when floating or sinking in water.

(i) True

(j) True

Question 2

Fill in the blanks:

(a) 1 kg is the mass of …………… mL of water at 4°C.

(b) Mass = density x …………… .

(d) Density of water is …………… kg m^-3.

(e) 1 g cm^-3 = …………… kg m^-3.

(f) The density of a body which sinks in water is …………… than 1000 kg m^-3.

(g) A body sinks in a liquid A, but floats in a liquid B. The density of liquid A is …………… 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 …………… than the density of body Y.

(i) The buoyant force experienced by a body when floating in salt-water is …………… that when floating in pure water.

(j) The weight of a body floating in a liquid is …………… .

Answer

(a) 1000

(b) volume

(d) 1000

(e) 1000

(f) more

(g) less

(h) more

(i) equal to

(j) zero

Question 3:

Match the following:

ICSE Physics Class 8 Notes 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 M kg substance”
D = MV = kgm3 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 x B x H or 43πr3or by measuring cylinder.

→ Mass is measured by beam balance or spring balance.

→ RELATIVE DENSITY : of substance is the density compared with water i.e. How many times the substance is DENSER than water. Since density of water is 1 gem-3, the density of a substance in g cm-3 = relative den.c ‘ty of substance.

S.I. unit of R.D → has no units → Since it is the ratio of the same quantities.

→ 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.