Tag: physics

Questions Related to physics

A hydrogen atom having kinetic energy $E$ collides with a stationary hydrogen atom. Assume all motions are taking place along the line of motion of the moving hydrogen atom. For this situation, mark out the correct statement(s)

physics nuclei nuclear force the nuclear force nuclear force and binding energy

  1. For $E\ge20.4\space eV$ only, collision would be elastic

  2. For $E\ge20.4\space eV$ only, collision would be inelastic

  3. For $E = 2.4\space eV$, collision would be perfectly inelastic

  4. For $E = 18\space eV$, the $KE$ of initially moving hydrogen atom after collision is zero

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Correct Option: B,D
Explanation:

K.E=2P.E
For electron in hydrogen to excite, a minimum of 10.2eV energy is required. Therefore, minimum 20.4eV K.E is required for inelastic collision otherwise, electron would not accept energy. And if E=20.4eV, collision would be perfectly inelastic.
If E is less than 20.4eV, collision is elastic and the two hydrogen atoms exchange velocities.
Therefore, B,D are the correct answers.

Regarding a nucleus, choose the correct options :

physics nuclei nuclear force the nuclear force nuclear force and binding energy

  1. Density of a nucleus is directly proportional to mass number A.

  2. Nucleus radius $ \propto {{A}^{1/3}}$

  3. Nuclear forces are dependent on the nature of nucleons.

  4. Nuclear forces are short range forces.

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Correct Option: B,D
Explanation:

Density of nucleus is: $\rho=\dfrac{A}{\dfrac{4}{3}\pi R^3}$
The radius of a nucleus, $R=r _0A^{1/3},$ so density of nucleus is independent of A and $R\propto {^3\sqrt{A}}$
The nuclear force is a short-range force because the distance between the nucleon is less than $0.7$ fermi (then the force is repulsive) and if greater than $10.7$ fermi (the force is attractive).

The CGS unit of power is $erg\ s^{-1}$

standardized measurement measurement of physical quantities need of unit for measurement measurements and experimentation physics

  1. True

  2. False

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Correct Option: A
Explanation:
Power is defined as the rate of doing work.
CGS unit of power is $erg \ s^{-1}$

The ratio of the C.G.S unit of pressure to the S.I unit of pressure is 10.

standardized measurement measurement of physical quantities need of unit for measurement measurements and experimentation physics

  1. True

  2. False

Show answer
Correct Option: B
Explanation:
SI unit of pressure is $N/m^2$ and CGS unit of pressure is $dyne/cm^2$.
We know that  $1 \ N = 10^5 \ dyne$  and   $1 \ m  =10^0 \ cm$
ratio of CGS unit to SI unit  $\dfrac{1 \ dyne/cm^2}{N/m^2} = \dfrac{1 \ dyne/cm^2}{10^5 \ dyne/(100)^2 \ cm^2} = \dfrac{1}{10} $
Thus the given statement is false.

The ratio of S.I. unit of thrust to the C.G.S unit of force is $10^5 : 1$

standardized measurement measurement of physical quantities need of unit for measurement measurements and experimentation physics

  1. True

  2. False

Show answer
Correct Option: A
Explanation:
S.I. unit of thrust (or force) is Newton  $(N)$ and C.G.S. unit is $dyne$.
We know that  $1 = N = 10^5 \ dynes$
Ratio of S.I. unit of force to C.G.S. unit is   $N:dyne = 10^5 :1$

The MKS unit of force is N.

standardized measurement measurement of physical quantities need of unit for measurement measurements and experimentation physics

  1. True

  2. False

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Correct Option: A
Explanation:

MKS unit of force is $kg \ m/s^2$ which is also expressed as Newton. Thus the above statement is true.

Dynes $cm^{-2}$ is the CGS unit of pressure.

standardized measurement measurement of physical quantities need of unit for measurement measurements and experimentation physics

  1. True

  2. False

Show answer
Correct Option: A
Explanation:
Pressure is defined as the force acting on the surface per unit its area.
CGS unit of pressure is  $dynes \ cm^{-2}$

Find the SI unit of the following derived quantities :

Pressure

standardized measurement measurement of physical quantities need of unit for measurement measurements and experimentation physics

  1. Pascal

  2. Newton

  3. Kg

  4. length

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Correct Option: A
Explanation:

Given pressure $\displaystyle = \frac{Force}{Area}$
$\therefore$ MKS unit of pressure $\displaystyle = \frac{S.I.  unit \ of \   force}{S.I.  unit \ of \ area} = \frac{kg  m  s^{-2}}{m^2}$
$\displaystyle = \frac{kg.m}{m^2 . s^2} = \frac{kg}{m.s^2}$
$\therefore$ MKS unit of pressure $= kg m^{-1} s^{-2}$
SI unit of pressure is pascal.

The C.G.S unit of speed is:

standardized measurement measurement of physical quantities need of unit for measurement measurements and experimentation physics

  1. cm/g

  2. m/s

  3. m/g

  4. cm/s

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Correct Option: D
Explanation:

The C.G.S. unit of speed is $ cm/s$.

C.G.S. units stand for centimetre–gram–second system of units.

Which system of units has been taken as standard?

standardized measurement measurement of physical quantities need of unit for measurement measurements and experimentation physics

  1. M.K.S

  2. C.G.S

  3. Both

  4. None

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Correct Option: A
Explanation:

In S.I system (standard international system), the units of mass,length and time are same,as that of M.K.S system. However , it is an enlarged system encompassing all fundamental units.