Tag: physics

Questions Related to physics

Boiling is a surface phenomenon.

  1. True

  2. False


Correct Option: B
Explanation:
The statement is false, boiling is a surface phenomenon.
Actually, boiling is a bulk a phenomenon. Heat energy goes to the entire bulk of liquid and it starts boiling. Whereas evaporation is a surface phenomenon

When salt is properly mixed with ice, then melting point of ice 

  1. is lowered

  2. remains the same

  3. is raised

  4. becomes infinite


Correct Option: A
Explanation:
When salt is mixed with ice, then melting point of ice is lowered.
This is the fact due to which salt is used to melt ice on the rod in winter.

Fill in the blanks :

The ........................... of water is defined as the constant temperature at which water changes to steam.

  1. melting point

  2. boiling point

  3. saturation point

  4. all of the above


Correct Option: B
Explanation:

Answer is B

The constant temperature at which a liquid boils and turns to vapour is known as boiling point.

Boiling of liquid can take place at any temperature. 

  1. True

  2. False


Correct Option: B
Explanation:

The boiling point of a liquid is the temperature at which its vapor pressure is equal to the pressure of the gas above it.

Vaporization takes place at all temperatures.

The saturated vapour pressure of water at $100^\circ C$ is

  1. 750 mm of Hg

  2. 760 mm of Hg

  3. 76 mm of Hg

  4. 7.6 cm of Hg


Correct Option: B
Explanation:

Vapour pressure or equilibrium vapour pressure or saturated vapour pressure is defined as the pressure exerted by a vapour in thermodynamic equilibrium with condensed phase at given temperature. At $100^oC$, the vapour pressure is $1atm$; i.e. 760mm of Hg i.e. 76cm of Hg as $1mm=10^{-1}cm$.

The water can be made to boil even at $0$ if the pressure of surrounding is:

  1. 56 cm of Hg

  2. 5 cm of Hg

  3. 0.1 cm of Hg

  4. 4.6 mm of Hg


Correct Option: A
Explanation:
The water can be made to boil even at $0^\circ C$. 
As we know, the ideal equation for gases is $pV=nRT$. Now, if $V$ and $n$ are taken constants, $p=cT$, where $c$ is a constant.
So pressure is directly proportional to the temperature.
Water boils at $100^\circ C$ or $373K$ at $1atm$ pressure. So, to obtain boiling at $0^\circ C$ or $273K$, you need to reduce the pressure to $\dfrac {273\times 1}{373} atm = 0.732 atm=56\text{cm of Hg}$(approx).

When 1 g of water at $100^\circ C$ gets converted into steam at the same temperature, the change in volume is approximately

  1. 1 cc

  2. 1000 cc

  3. 1500 cc

  4. 1670 cc


Correct Option: D
Explanation:

During change of state mass does not change.

Mass of water = 1gm
So mass of steam is also= 1gm
Density of steam =$0.0006gm/cm^3$
Initail volume of water =1$cm^3$(Density =$1gm/cm^3$) ($1=\dfrac { 1 }{ V } $) $,v=1cm^3$
Later volume of water converted to steam =$\dfrac { mass\quad of\quad steam }{ Density\quad of\quad steam } $
$=\dfrac { 1 }{ 0.0006 } $
$=\dfrac { 10000 }{ 6 } { cm }^{ 3 }$
$= 1670cm^3$
Change of volume = $1670cm^3$

On increasing the external pressure , the boiling point of liquid 

  1. is raised

  2. is lowered

  3. remain unaffected

  4. uncertain


Correct Option: A
Explanation:
On increasing the external pressure, the boiling point of liquid is increased.
Boiling point is the temperature at which vapor pressure of the liquid equals to the external pressure.
V.P, of liquid is a function of temperature.
Now, if we increase the external pressure, a higher temperature would be required so that V.P. equals to external pressure.

Rice takes longest time to cook

  1. at sea level

  2. at shimla

  3. at Mount Everest

  4. in a submarine 100 m below the surface of sea


Correct Option: C
Explanation:

At higher altitude, water starts boiling at lower temperature and heat required for cooking food is not available, because heat escapes in form of water vapour. So, rice takes longer time to cook at Mount Everest

Temperature at which liquid changes to gaseous state

  1. Freezing point

  2. Boiling point

  3. Neutral state

  4. None


Correct Option: B
Explanation:

boiling point is a temperature state when liquid state starts charging into gaseous state.