# AFCAT: Physics MCQs (Practice_Test 15 of 35)

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Maxwell's thermodynamic relations connect coordinate derivatives evaluated at

two different equilibrium positions along a single reversible path

two equilibrium positions along two different reversible paths

a single equilibrium positions along two different reversible paths

a single equilibrium position along one reversible path

The volume of a certain mass of gas at constant pressure is doubled to its value at 00C. The temperature of the gas will be

1000C

1730C

2730C

5460C

The period of oscillations of a galvanometer mirror due to the Brownian motion is 40 s. The moment of inertia of the galvanometer about its suspension axis is 8 × 10 − 12kg-m2. The root-mean-square of maximum deflection of this mirror at a temperature of 500C, is

2.7 × 10 − 4 rad

2.1 × 10 − 4rad

1.5 × 10 − 4rad

0.9 × 10 − 4rad

In the porous plug experiment, the temperature of the gas increases after throttling. The correct range for the initial temperature of the gas for this to happen is

boiling temperature to critical temperature

critical temperature to Boyle's temperature

Boyle's temperature to inversion temperature

below inversion temperature

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

7/5

5/3

4/3

3/2

A long straight vertical wire carries a current of 10A directed upwards. If the horizontal component of the earth's magnetic field at the plane is 2 × 10 − 5 T, then the distance of the point from the wire at which the net B is zero, is

0.05m

0.10m

(0.05) pm

(0.1) pm

A wire bent into the form of an ellipse has semilatus rectum L and eccentricity a. For a current I in the wire, the magnetic field at one of the foci of the ellipse will be

m0I/2L

m0I/L

ma0I/2L

ma0I/L

If the B-H curves of two samples of P and Q of iron are as shown above, then which one of the following statements is correct?

Both P and Q are suitable for matching permanent magnets

P is suitable for making permanent magnets and Q for matching electromagnets

P is suitable for making electromagnets and Q is suitable for permanent magnets

Both P and Q are suitable for making electromagnets

One billion electrons are placed on a solid copper sphere. If this system attains equilibrium, then the electrons will be

uniformly distributed on the surface of the sphere

uniformly distributed in the interior of the sphere

concentrated at the centre of the sphere

concentrated at the bottom of the sphere

If two infinite oppositely charged plates with surface charge density I s I on each plate are kep perpendicular to each other as shown in the above figure, then a charge q at p will experience a force

sq/20 away towards the vertical plate

sq/20 away from the horizontal plate

sq/rt20 towards the origin, 0

sq/rt20 making 450 with respect to the vertical direction

The above figure shows electric field E at distance r in any direction from the origin O. The electric field E is due to

a charged hollow metallic sphere of radius OP with centre at O

a charged solid metallic sphere of radius OP with centre at O

a uniformly charged non-conducting sphere of radius OP with centre at O

a uniformly charged non-conducting hollow sphere radius OP with centre at O

The capacitance of a parallel plate capacitor is 2 × 10 − 6 F. It changes to 2 × 10 − 6 F when a dielectric is inserted between the plates. The relative permitivity of the dielectric is

20

2

1

½

A parallel plate capacitor has an electric field of 10s V/M between the plates. If the charge on the capacitor plate is 1 mc, then the force on each capacitor plate is

0.1 N

0.05 N

0.02 N

0.01 N.

In the circuit shown in the above figure, the resultant resistance between P and Q is

5 W

14W

15W

20W

A conductor wire, having 1Q29 free electrons per m3 carries a current of 20 A. If the cross-section of wire is 1 mm2 then the drift velocity of electrons will be of the order of

10 − 5 m/s

10 − 3 m/s

10 − 1 m/s

10 ms