# Punjab PSC Exam: Physics MCQs (Practice_Test 22 of 35)

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- The gibb՚s function G in thermodynamics is defined as G = H-TS where H is the enthalpy, T is the temperature and S is the entropy. In an isothermal, isobaric, reversible process, G
- remains constant, but not zero
- varies linearly
- varies non-linearly
- is zero

- Average of squares of displacements of particles in Brownian motion is
- Directly proportional to temperature-T
- directly proportional to viscosity-h
- Directly proportional to radius of the particle-a
- directly proportional to time-t

- The order of magnitude of the mean free path of a diatomic molecule at STP is
- 1 cm
- 10 − 2 cm
- 10 − 5
- 10 − 8 cm

- In the Vander Walls equation (p + a/v2) (v-b) = RT
- ‘a’ and ‘b’ are the corrections for the cohesive forces
- ‘a’ and ‘b’ are the corrections for the volume occupied by. The molecules
- ‘a’ is the correction for the cohesive forces and ‘b’ is the correction for the volume occupied by the molecules
- ‘a’ is the correction for the volume occupied by the molecules and ‘b’ is the correction for the cohesive forces

- After Joule-Thomson expansion, the gas is
- always heated
- heated or cooled depending upon the initial temperature of the gas
- neither heated nor cooled at any temperature
- always cooled

- If a black body radiation in a spherical cavity of volume V satisfies the relation, PVh = constant during a quasi-static isentropic process, then the numerical value of h should be
- ()
- ()
- ()
- ()

- Consider the following statements regarding the paramagnetic materials:
- Permanent magnetic moments interact with each other weakly.
- Magnetization M varies inversely with absolute temperature T.
- Magnetization M is much greater than the magnetic filed strength H.
- Large permanent magnetization can be. Induced in these materials.

Of these statements

- 1 and 2 are correct
- 2 and 4 are correct
- 1,2 and 3 are correct
- 1,3 and 4 are correct

- If a Rowland ring of mean radius 0.1 m had 2000 turns of wire wound on a ferromagnetic core of h = 1000, then, for a magnetizing current of 1.5 A, the magnetic field in the core would be
- 3 T
- 6 T
- 9 T
- 12 T

- The electric potential point (x, y) in the x-y plane is given by V =-kxy. The field intensity at a distance ‘r’ from the origin varies as
- r2
- r
- 1/r
- 1/r2

- A fast electron having a kinetic energy of 3.0 × 10 − 17 Joule enters a region of space containing a uniform electric field of E = 1000 volts/m. The field is parallel to the electron՚s motion and in a direction such as to decelerate it. The distance traveled by the electron before it is brought to rest (charge of electron = 1.6 × 10 − 19 C) will be
- 1.875 cm
- 18.75 cm
- 187.5 cm
- 1875 cm

- At a point 20 cm from the centre of a uniformly k charged dielectric sphere of radius 10 cm, the electric field is 100 V/m. The electric field at3 cm from the centre of the sphere will be
- 150 V/m
- 125 V/m
- 120 V/m
- zero

- Two identical charged spheres of density 2.4 gm/cm3 suspended from the same point by strings of equal length 1.5 m, make an angle of 30 degree in air. If suspended in a liquid of density 0.8 gm/cm3 the angle remains the same. The dielectric constant of the liquid is
- 1.2
- 1.5
- 2.4
- 3.0

- Which one of the following statements regarding the electric fields E1 = xi + yi and E2 = xy2 i + y3 j is correct?
- Both E1 and E2 can represent electrostatic field
- Neither E1 nor E2 can represent electrostatic field
- Only E1 can represent electrostatic field
- Only E2 can represent electrostatic field

- The equivalent capacitance of the given circuit is
- 0.5 m f
- 1 m f
- 6.75 m f
- 9 m f

- Consider the following statements: In electronics, capacitors are used for
- tuning the resonant circuits.
- bypassing alternating voltages.
- storing electrical energy in the form of magnetic field.
- blocking D C voltages from parts of an electrical circuit.

Of these statements

- 1,2 and 4 are correct
- 1 and 2 are correct
- 2,3 and 4 are correct
- 1 and 4 are correct