Physics Test 169

Result

Physics Test 169

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Weekly Quiz Competition

Question 1
4 / -1

n moles of a gas filled in a container at temperature T is in thermodynamic equilibrium initially. If the gas is compressed slowly and isothermally to half its initial volume the work done by the atmosphere on the piston is:

A
nRT/2

B
-nRT/2

C

D
-nRT ln2

Solution
Question 2
4 / -1

In a process the pressure of an ideal gas is proportional to square of the volume of the gas. If the temperature of the gas increases in this process, then work done by this gas:

A
is positive

B
is negative

C
is zero

D
may be positive

Solution

As p ∝ V²

T ∝ V³

i.e. if temperature increases, volume also increases hence work done will be positive.
Question 3
4 / -1

A vessel contains an ideal monoatomic gas which expands at constant pressure, when heat Q is given to it. Then the work done in expansion is:

A
Q

B
3/5 Q

C
2/5 Q

D
2/3 Q

Solution
Question 4
4 / -1

5 moles of Nitrogen gas is enclosed in an adiabatic cylindrical vessel. The piston itself is a rigid light cylindrical container containing 3 moles of Helium gas. There is a heater which gives out a power 100 cal/sec to the nitrogen gas. A power of 30 cal /sec is transferred to Helium through the bottom surface of the piston. The rate of increment of temperature of the nitrogen gas assuming that the piston moves slowly:

A
2 K/sec

B
4 K/sec

C
6 K/sec

D
8 K/sec

Solution

Net power given to N₂ gas = 100 - 30 = 70 calls

The nitrogen gas expands isobarically.
Question 5
4 / -1

The gas law PV/2 =constant for a given amount of a gas is true for :

A
isothermal change only.

B
adiabatic change only.

C
both isothermal & adiabatic changes

D
neither isothermal nor adiabatic change

Solution

As PV = nRT

For n = constant constant for all changes Hence (C)
Question 6
4 / -1

All the rods have same conductance ‘K’ and same area of cross section S. If ends A and C are maintained at temperature 2T₀ and T₀ respectively then which of the following is/are correct:

A
Rate of heat flow through ABC, AOC and ADC is same

B
Rate of heat flow through BO and OD is not same

C
Total Rate of heat flow from A to C is

D
Temperature at junctions B, O and D are same

Solution

By symmetry

I_AB = I_BC & I_AD = I_DC

∴ No current in BO and OD

∴ TB = T_O = T_D
Question 7
4 / -1

A hollow copper sphere and a hollow copper cube, of same surface area and negligible thickness, are filled with warm water of same temperature and placed in an enclosure of constant temperature, a few degrees below that of the bodies. Then in the beginning :

A
the rate of energy lost by the sphere is greater than that by the cube

B
the rate of fall of temperature for sphere is greater than that for the cube.

C
the rate of energy lost by the sphere is less than that by the cube

D
the rate of fall of temperature for sphere is less than that for the cube.

Solution
Question 8
4 / -1

The colour of a star indicates its :

A
weight

B
size

C
temperature

D
distance

Solution

The colour of an object indicates the rate at which energy is emitted and hence indicates the temperature.
Question 9
4 / -1

Two identical solid spheres have the same temperature. One of the sphere is cut into two identical pieces. The intact sphere radiates an energy Q during a given small time interval. During the same interval, the two hemispheres radiate a total energy Q'. The ratio Q'/Q is equal to :

A
2.0

B
4.0

C
2/3

D
1.5

Solution
Question 10
4 / -1

A calorimeter contains 50 g of water at 50°C. The temperature falls to 45°C in 10 minutes. When the calorimeter contains 100 g of water at 50°C, it takes 18 minutes for the temperature to become 45°C. then the water equivalent of the calorimeter is :

A
12.5 g

B
6.25 g

C
25 g

D
15 g

Solution