Tag: physics

Questions Related to physics

The height of a mercury barometer is 75$\mathrm { cm }$ at sealevel and 50$\mathrm { cm }$ at the top of a hill. Ratio of density ofmercury to that of air is $10 ^ { * }$ . The height of the hill is 

various types of barometer fluids physics

  1. 250$\mathrm { m }$

  2. 2.5$\mathrm { km }$

  3. 1.25$\mathrm { km }$

  4. 750$\mathrm { m }$

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Correct Option: C

The value of $\mathrm { g }$ at a place decreases by 2$\%$ . The barometric height of mercury 

various types of barometer fluids physics

  1. Increases by 2$\%$

  2. Decreases by 2$\%$

  3. Remains unchanged

  4. Sometimes increases and so

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Correct Option: A

Eight identical spherical mercury drops charged to a potential of $20V$ each are coalesced into a single spherical drop.

various types of barometer fluids physics

  1. The internal Energy of the system remains the same.

  2. The new potential of the drop is $80V$

  3. Internal energy of the system decreases

  4. The potential remains the same i.e., $20V$

Show answer
Correct Option: B
Explanation:

Potential of one small drop of mercury, 
$V=\displaystyle\frac{kq}{r}=20V$
Volume of big drop=volume of $8$ small drops
$\displaystyle\frac{4}{3}\pi R^3=8\times \frac{4}{3}\pi r^3\Rightarrow =2r$
$Q'=8q$
Potential of big drop,
$\displaystyle V'=\frac{kQ'}{R}=\frac{K\times 8q}{2r}=\frac{4kq}{r}=4\times 20=80V$
Hence, option $B$ is the correct answer.

A cubical block of steel of each side equal 1 is floating on mercury in vessel. The densities of steel and mercury are $ \rho _s and \rho _m $.The height of the block above the mercury level is given by 

various types of barometer fluids physics

  1. $ I \left( 1+\dfrac { \rho _ s }{ \rho _ m } \right) $

  2. $ I \left( 1-\dfrac { \rho _ s }{ \rho _ m } \right) $

  3. $ I \left( 1+\dfrac { \rho _ m }{ \rho _ s } \right) $

  4. $ I \left( 1-\dfrac { \rho _ m }{ \rho _ s} \right) $

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Correct Option: B

A beaker contining a liquid is kept inside a big closed jar. If the air inside the jar is continuously pumped out, the pressure in the liquid near the bottom of the liquid will

various types of barometer fluids physics

  1. Increase

  2. Decrease

  3. Remain constant

  4. First decrease and then increase

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Correct Option: B

A thin tube of uniform cross - section is sealed at both ends. It lies horizontally, the middle $5 \,cm$ containing mercury and the two equal ends containing air at the same pressure P. When the tube is held at an angle $60^o$ with the vertical, the lengths of the air column above and below the mercury are $46$ and $44.5$ cm respectively. Calculate the pressure P, in cm of Hg. (The temperature of the system is kept at $30$ K)

various types of barometer fluids physics

  1. $92.5$ cm of Hg

  2. $75.4$ cm of Hg

  3. $73.0$ cm of Hg

  4. $70.5$ cm of Hg

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Correct Option: B

In a certain region of space, there are n molecules per unit volume. The temperature of the gas T. The pressure of the gas will be: 

various types of barometer fluids physics

  1. $nRT$

  2. $nkT$

  3. $\dfrac{{nT}}{k}$

  4. $\dfrac{{nT}}{R}$

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Correct Option: B

How is the barometric height of a simple barometer affected if
(a) its tube is pushed down into the trough of mercury?
(b) its tube is slightly tilted form vertical?
(c) a drop of liquid is inserted inside the tube?

various types of barometer fluids physics

  1. (a) remains unaffected (b) increases (c) decreases

  2. (a) decreases (b) increases (c) decreases

  3. (a) increases (b) remains unaffected (c) increases

  4. (a) remains unaffected (b) remains unaffected (c) decreases

Show answer
Correct Option: D
Explanation:

Below are the answers:
(a) Mercury in the tube adjusts until the weight of the mercury column balances the atmospheric force exerted on the reservoir. High atmospheric pressure places more force on the reservoir, forcing mercury higher in the column. Low pressure allows the mercury to drop to a lower level in the column by lowering the force placed on the reservoir.
When the tube is pushed down into the trough of mercury the height of mercury column above the surface of the bottom surface remains the same. 


(b) When the tube is slightly tilted form vertical, there is no change in the height of the mercury in the tube.

(c) If the vacuum is replaced with a drop, then the drop will exert some pressure on the mercury and there will be inaccurate readings on the barometer. The barometric height is decreased in this case. So, vacuum is present on top of the mercury inside the tube.

Which of the following is not a reason why mercury is preferred as a barometric liquid?

various types of barometer fluids physics

  1. Mercury has high density

  2. Mercury does not wet the glass

  3. Mercury is opaque and shiny

  4. Mercury is poisonous

Show answer
Correct Option: D
Explanation:

1) It has $13.5$ times higher density than water
2) It doesn't stick to the glass walls of tube like water does.

3) It is opaque and shiny

Atmospheric pressure at a place is $66cm$ of mercury. This place is

various types of barometer fluids physics

  1. $1250m$ above sea level

  2. $1250m$ below sea level

  3. $125m$ above sea level

  4. at the sea level

Show answer
Correct Option: A
Explanation:

Atmospheric pressure at the place is equivalent to that of $66cm$ of mercury.
We know that atmospheric pressure at the sea level is equivalent to that of $76cm$ of mercury.
So, pressure at that place is less by $(76-66)=10cm$ of mercury.
We know that atmospheric pressure decreases by $1cm$ for every $125m$ increase in altitude.
So, the concerned place is $(125 \times 10)m=1250m$ above the sea level.