Science (English Medium) कक्षा ११ - CBSE Question Bank Solutions for Physics

The temperature and relative humidity in a room are 300 K and 20% respectively. The volume of the room is 50 m³. The saturation vapour pressure at 300 K 3.3 kPa. Calculate the mass of the water vapour present in the room.

Use R = 8.3 J K^-1 mol^-1

The temperature and the relative humidity are 300 K and 20% in a room of volume 50 m³. The floor is washed with water, 500 g of water sticking on the floor. Assuming no communication with the surrounding, find the relative humidity when the floor dries. The changes in temperature and pressure may be neglected. Saturation vapour pressure at 300 K = 3.3 kPa.

Use R = 8.31 J K^-1 mol^-1

A bucket full of water is placed in a room at 15°C with initial relative humidity 40%. The volume of the room is 50 m3. (a) How much water will evaporate? (b) If the room temperature is increased by 5°C, how much more water will evaporate? The saturation vapour pressure of water at 15°C and 20°C are 1.6 kPa and 2.4 kPa respectively.

Use R = 8.3 J K^-1 mol^-1

Assume that the total surface area of a human body is 1.6 m² and that it radiates like an ideal radiator. Calculate the amount of energy radiated per second by the body if the body temperature is 37°C. Stefan constant σ is 6.0 × 10⁻⁸ W m⁻² K⁻⁴.

A solid aluminium sphere and a solid copper sphere of twice the radius are heated to the same temperature and are allowed to cool under identically surrounding temperatures. Assume that the emissivity of both the spheres in the same. Find the ratio of (a) the rate of heat loss from the aluminium sphere to the rate of heat loss from the copper sphere and (b) the rate of fall of temperature of the aluminium sphere to the rate of fall of temperature of the copper sphere. The specific heat capacity of aluminium = 900 J kg⁻¹°C⁻¹ and that of copper = 390 J kg⁻¹°C⁻¹. The density of copper = 3.4 times the density of aluminium.

A spherical ball A of surface area 20 cm² is kept at the centre of a hollow spherical shell B of area 80 cm². The surface of A and the inner surface of B emit as blackbodies. Both A and B are at 300 K. (a) How much is the radiation energy emitted per second by the ball A? (b) How much is the radiation energy emitted per second by the inner surface of B? (c) How much of the energy emitted by the inner surface of B falls back on this surface itself?

A cylindrical rod of length 50 cm and cross sectional area 1 cm² is fitted between a large ice chamber at 0°C and an evacuated chamber maintained at 27°C as shown in the figure. Only small portions of the rod are inside the chamber and the rest is thermally insulated from the surrounding. The cross section going into the evacuated chamber is blackened so that it completely absorbs any radiation falling on it. The temperature of the blackened end is 17°C when steady state is reached. Stefan constant σ = 6 × 10⁻⁸ W m⁻² K⁻⁴. Find the thermal conductivity of the material of the rod.

Calculate the amount of heat radiated per second by a body of surface area 12 cm² kept in thermal equilibrium in a room at temperature 20°C. The emissivity of the surface = 0.80 and σ = 6.0 × 10⁻⁸ W m⁻² K⁻⁴.

The variation of quantity A with quantity B, plotted in figure describes the motion of a particle in a straight line.

1. Quantity B may represent time.
2. Quantity A is velocity if motion is uniform.
3. Quantity A is displacement if motion is uniform.
4. Quantity A is velocity if motion is uniformly accelerated.

A person of mass 50 kg stands on a weighing scale on a lift. If the lift is descending with a downward acceleration of 9 ms^–2, what would be the reading of the weighing scale? (g = 10 ms^–2)

Calculate the power of a crane in watts, which lifts a mass of 100 kg to a height of 10 m in 20s.

The average work done by a human heart while it beats once is 0.5 J. Calculate the power used by heart if it beats 72 times in a minute.

A stone of mass m is tied to an elastic string of negligble mass and spring constant k. The unstretched length of the string is L and has negligible mass. The other end of the string is fixed to a nail at a point P. Initially the stone is at the same level as the point P. The stone is dropped vertically from point P.

1. Find the distance y from the top when the mass comes to rest for an instant, for the first time.
2. What is the maximum velocity attained by the stone in this drop?
3. What shall be the nature of the motion after the stone has reached its lowest point?

The angle of contact at the interface of water-glass is 0°, Ethylalcohol-glass is 0°, Mercury-glass is 140° and Methyliodide-glass is 30°. A glass capillary is put in a trough containing one of these four liquids. It is observed that the meniscus is convex. The liquid in the trough is ______.

For a surface molecule ______.

1. the net force on it is zero.
2. there is a net downward force.
3. the potential energy is less than that of a molecule inside.
4. the potential energy is more than that of a molecule inside.

Is surface tension a vector?

The sap in trees, which consists mainly of water in summer, rises in a system of capillaries of radius r = 2.5 × 10^–5 m. The surface tension of sap is T = 7.28 × 10^–2 Nm^–1 and the angle of contact is 0°. Does surface tension alone account for the supply of water to the top of all trees?

The free surface of oil in a tanker, at rest, is horizontal. If the tanker starts accelerating the free surface will be titled by an angle θ. If the acceleration is a ms^–2, what will be the slope of the free surface?

Two mercury droplets of radii 0.1 cm. and 0.2 cm. collapse into one single drop. What amount of energy is released? The surface tension of mercury T = 435.5 × 10^–3 Nm^–1.

Two mercury droplets of radii 0.1 cm. and 0.2 cm. collapse into one single drop. What amount of energy is released? The surface tension of mercury T = 435.5 × 10^–3 Nm^–1.