Tag: physics

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Questions Related to physics

Multiple choice intermolecular forces: cohesive and adhesive forces surface tension properties of matter physics

On a clean glass plate a drop of water spreads to form a thin layer whereas a drop of mercury remains almost spherical because

  1. mercury is a metal

  2. density of mercury is greater than that of water

  3. cohesion of mercury is greater than its adhesion with glass

  4. cohesion of water is greater than its adhesion with glass
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Mercury remains spherical on a glass plate due to greater cohesive force between mercury molecules than adhesive force between mercury and glass plate.

Multiple choice intermolecular forces: cohesive and adhesive forces surface tension properties of matter physics

A capillary tube of radius $0.25\ mm$ is submerged vertically in water so that $25\ mm$ of its length outside water. The radius of curvature of the meniscus will be $(T = 7.5\times 10^{-3} N/m)$.

  1. $0.2\ mm$

  2. $0.4\ mm$

  3. $0.6\ mm$

  4. $0.8\ mm$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$h= \dfrac{2T}{dgx}$

$h= \dfrac{2\times 7.5 \times {10}^-3} {1000 \times 10 \times d}$
$h=25mm$
$d= 0.6 mm$

Multiple choice modelling gases - the kinetic model ideal gases kinetic theory of gases physics

The gas, which is present the most in air, is___

  1. oxygen

  2. nitrogen

  3. carbon dioxide

  4. water vapour
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

1) Nitrogen $-78$%

2) Oxygen $-21$%
3) Inert Nobel gases $-0.9$%
4) Several trace gases $-0.1$%
The above list the different number of gases in descending order. As per the list clearly Nitrogen is the gas present in most air.

Multiple choice modelling gases - the kinetic model ideal gases kinetic theory of gases physics

Heat is associated with 

  1. kinetic energy of random motion of molecules

  2. kinetic energy of orderly motion of molecules

  3. total kinetic energy of random and orderly motion of molecules

  4. kinetic energy of random motion in some cases and kinetic energy orderly motion in other.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Heating up a substance excites the molecules of that substance making  the molecules moves vigorously thus giving velocity to the molecules and we know kinetic energy of a body is by the virtue of its motion.       

Multiple choice modelling gases - the kinetic model ideal gases kinetic theory of gases physics

The kinetic energy of translation of $20gm$ of oxygen at $47^oC$ is (molecule wt. of oxygen is $32gm/mol $and $R=8.3J/mol/K$)

  1. 2490 joules

  2. 2490 ergs

  3. 830 joules

  4. 124.5 joules
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Kinetic energy K = (3/2)nRT. For 20g of oxygen (molar mass 32g/mol), n = 20/32 = 0.625 mol. T = 47 + 273 = 320 K. K = (3/2) * 0.625 * 8.3 * 320 = 2490 J.

Multiple choice modelling gases - the kinetic model ideal gases kinetic theory of gases physics

Statement 1: The internal energy of a perfect gas is entirely kinetic and depends only on absolute temperature of the gas and not on its pressure or volume.
Statement 2: A perfect gas is heated keeping pressure constant and later at constant volume. For the same amount of heat the temperature of the gas at constant pressure is lower than that at constant volume.

  1. Statement 1 is true, statement 2 is true and statement 2 is correct explanation of statement 1

  2. statement 1 is true, statement 2 is false

  3. Statement 1 is true, Statement 2 is true but Statement 2 is not the correct explanation of Statement 1

  4. Statement 1 is false, Statement 2 is true
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Statement 1 is true as internal energy of an ideal gas depends only on temperature. Statement 2 is true because at constant pressure, some heat is used for work (expansion), leaving less for temperature rise compared to constant volume. However, Statement 2 does not explain Statement 1.

Multiple choice modelling gases - the kinetic model ideal gases kinetic theory of gases physics

The average pressure of an ideal gas is  

  1. $\rho = (1/3)\, mn \, V^2 _{av}$

  2. $\rho = (1/2)\, mn \, V _{av}$

  3. $\rho = (1/4)\, mn \, V^2 _{av}$

  4. $\rho = (1/3)\, mn \, V _{av}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

From the kinetic theory of gases, the pressure exerted by an ideal gas is given by P = (1/3) * rho * v_rms^2, where rho is density (m*n) and v_rms^2 is the mean square speed (V^2_av).