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# JEE Physics 2011 Exam Questions

#### Multiple Choice Questions

11.

A fully charged capacitor C with initial charge q0 is connected to a coil of self inductance L at t = 0. The time at which the energy is stored equally between the electric and the magnetic fields is

A.

As initially, charge is maximum
∴ q = qocos ωt
Current,

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12.

A thermally insulated vessel contains an ideal gas of molecular mass M and ratio of specific heat γ.It is moving with speed v and it suddenly brought to rest. Assuming no heat is lost to the surroundings, its temperature increases by

C.

As no heat is lost, therefore,
Loss of kinetic energy = Gain of internal energy of gas
i.e.,

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13.

A boat is moving due east in a region where the earth's magnetic field is 5.0 × 10-5 NA-1m-1 due north and horizontal. The boat carries a vertical aerial 2m long. If the speed of the boat is 1.50 ms-1, the magnitude of the induced emf in the wire of aerial is

• 0.75 mV

• 0.50 mV

• 0.15 mV

• 1 mV

C.

0.15 mV

Eind = B × v × l
= 5.0 × 10-5 × 1.50 × 2
= 10.0 × 10-5 × 1.5
= 15 × 10-5 vot.
= 0.15 mv

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14.

Water is flowing continuously from a tap having an internal diameter 8 × 10-3 m. The water velocity as it leaves the tap is 0.4 ms-1. The diameter of the water stream at a distance 2 × 10-1 m below the tap is close
to:

• 7.5 x 10-3 m

• 9.6x 10-3 m

• 3.6x 10-3 m

• 5.0x 10-3 m

C.

3.6x 10-3 m

From Bernoulli's theorem

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15.

Three perfect gases at absolute temperature T1, T2 and T3 are mixed. The masses of molecules are m1,m2 and m3 and the number of molecules is n1,n2 and n3 respectively.Assuming no loss of energy, the final temperature of the mixture is

A.

For adiabatic process i.e., no heat change

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16.

A current I flows in an infinitely long wire with cross-section in the form of a semicircular ring of radius R. The magnitude of the magnetic induction along its axis is

D.

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17.

A mass M, attached to a horizontal spring, executes SHM with an amplitude A1. When the mass M passes through its mean position than a smaller mass m is placed over it and both of them move together with amplitude A2. The ratio of (A1/A2) is

C.

At mean position, Fnet = 0
Therefore, By conservation of linear momentum,
Mv1 = (M+m)v2
1A1 = (M+m)ω2A2
⇒

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18.

Two particles are executing simple harmonic motion of the same amplitude Aand frequency ω along the x - axis. Their mean position is separated by distance X0 (X0 >A). If the maximum separation between them is (X0 + A), the phase difference between their motion is

• π/3

• π/4

• π/6

• π/2

A.

π/3

x1 = A sin( ωt + Φ1)
x2 = A sin( ωt + Φ2)

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19.

100g of water is heated from 30°C to 50°C ignoring the slight expansion of the water, the change in its internal energy is (specific heat of water is 4184 J/Kg/K)

• 8.4 kJ

• 84 kJ

• 2.1 kJ

• 4.2 kJ

A.

8.4 kJ

ΔQ = M,S,ΔT
= 100 × 10-3 × 4.184 × 20 = 8.4 × 103
ΔQ = 84 kJ, ΔW = 0
ΔQ = ΔV + ΔW
ΔV = 8.4 kJ

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20.

A Carnot engine operating between temperatures T1 and T2 has efficiency 1/6. When T2 is lowered by 62 K, its efficiency increases to 1/3. Then T1 and T2 are, respectively

• 372 K and 330 K

• 330 K and 268 K

• 310 K and 248 K

• 372 K and 310 K

D.

372 K and 310 K

The efficiency  is given by,

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