[2 Mark Question Answer]

Question 12 Marks

Explain how the density of a substance varies with change in temperature.

Answer

In case of solids, there is no significant change in their densities with change in temperature. In case of liquids and gases, the densities increase with decrease in temperature and decrease with increase in temperature.

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Question 22 Marks

Why is a Plimsoll line a safety requirement for ships?

Answer

A Plimsoll line indicates the level up to which a ship should be submerged safely in a particular sea or river. If a ship is loaded beyond its Plimsoll line, it runs the risk of sinking.

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Question 32 Marks

Define the relative density of a substance. Why does relative density have no units?

Answer

Relative density of a substance is defined as the ratio of the density of the substance to the density of water at $4 ^\circ C$. As relative density is a ratio of the same physical quantities, therefore, it has no unit.

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Question 42 Marks

A liquid with mass $75 g$ is poured into a measuring cylinder $($Fig. $2)$

Answer

Mass of liquid, $m =75 g$
Volume of the liquid, $V =92\ mL$
Density of the liquid $=\frac{m}{V}$
$ =\frac{75 g}{92\ mL}$
$=0.82\ g / mL $

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Question 52 Marks

A liquid of mass $1196\ g $ is poured into a measuring cylinder $($Fig. $1)$

Answer

Mass of liquid, $m =1196\ g$
Volume of the liquid, $V =75\ mL$
Density of the liquid $=\frac{m}{V}=\frac{1196 g}{75 mL}$
$=15.95\ g / mL$

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Question 62 Marks

The capacity of an $RD$ bottle is $100\ cc$ and its mass is $45\ g$. Find the mass of the bottle when it is filled with a liquid of density $600\ kg / m ^3$.

Answer

Mass of empty $RD$ bottle, $ml =45 g$
Capacity of $R D$ bottle, $V=100\ cm^3$ Density of the liquid filled in the bottle $=600$ $ kg / m ^3=0.6 g / cm ^3 $
Mass of the liquid filled in the bottle,
$m _2 -$ Density of liquid filled in it $\times V$
$ =0.6 g / cm ^3 \times 100\ cm^3=60 g $

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Question 72 Marks

The relative density of oak wood is $0.64$. What is its density in
$a.$ the $\text{SI}$ system?
$b.$ the $\text{CGS}$ system?
Relative density of oak wood $= 0.64$

Answer

$a.$ In $\text{SI}$ system, density of oak wood $=$ relative density of oak wood $\times 1000\ kg / m ^3$
$=0.64 \times 1000\ kg / m ^3$
$=640\ kg / m ^3$
$b.$ In $\text{CGS}$ system, density of oak wood $=$ relative density of oak wood $ \times\ lg / cm ^3$
$=0.64 \times 1 g / cm ^3$
$=0.64 g / cm ^3$

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Question 82 Marks

A piece of a solid has a mass of $10 g.$ When it is completely immersed in water, the water level rises by $5 \ mL$. Determine the density of the solid.

Answer

Mass of the piece of solid, $m = 10 g$
Rise in level of water when the solid is immersed in it, $V = 5\ mL$
Volume of the solid $= V = 5\ mL$
Density of the solid = $\frac{m}{v}=\frac{10 g}{5 mL}= 2 g/mL$

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Question 92 Marks

How can the knowledge of relative density help in verifying the purity of substances ?

Answer

Suppose you are given a sample of the substance and you need to verify its purity. First, find out the relative density
of the substance $(r)$. Then, you should determine the relative density of the sample. Let us say it comes out to be $r$ If $r’ = r$, then the substance is pure or else it is impure.

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Question 102 Marks

Ankur goes to a jewellery shop and buys a gold locket. When he comes back home, he looks up the density of gold, which he finds to be $19.3 g/cm^3.$ How can he determine if the locket he has bought is of pure gold?

Answer

Ankur should determine the volume and mass of the locket and calculate its density. If it matches with the density of pure gold, then the locket is made up of pure gold. If it is less than the density of pure gold, then the locket he has bought is impure.

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Question 112 Marks

A test tube filled with a solid sinks $($to a certain mark$)$ in a container filled with milk. If water is added to the milk, will the test tube sink more or will it move up in the container?

Answer

As density of water is less than that of milk, so when water is mixed with milk, the density of the mixture in the container decreases. So, the test tube will sink more.

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Question 122 Marks

Which of the following bodies will sink or float in water and why?
$a.$ A body having a relative density of $1.2$
$b.$ A body having a relative density of $0.8$

Answer

$a:$ A body having a relative density of $1.2$ will sink in water as its density is more than that of water.
$b:$ A body having a relative of $0.8$ will float in water as its density is less than that of water.

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PHYSICS [2 Mark Question Answer]

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