Physics: Mechanics: UPSC Previous Year Questions (Science and Technology)

Explanation

Surface tension is the force that acts on the surface of a liquid, causing it to contract and minimize its surface area. This effect occurs because molecules at the surface of the liquid experience a net inward force due to the attractive forces between the molecules. As a result, the liquid tends to form shapes that have the least surface area, such as spherical droplets. This tendency to minimize surface area is why liquid droplets form spherical shapes in free space, as a sphere has the smallest surface area for a given volume.

Explanation

A vector quantity is a physical quantity that has both magnitude and direction. In addition to how much of a quantity there is, you also need to know the direction in which it acts. Some examples of vector quantities include force, velocity, acceleration and displacement. Momentum is a vector quantity because it has both magnitude and direction (it depends on the direction of motion and the velocity of the object).

Explanation

Option (a) is correct: The working principle of a washing machine is Centrifugation. It is a process used to separate substances of different densities by spinning them at high speed. In a washing machine, the centrifugal force generated during the spin cycle helps remove water from the clothes along with dirt and stain.

Option (b), (c) and (d) are incorrect:

Dialysis is a process used to remove waste products and excess fluids from the blood in patients with kidney failure. It involves the diffusion of solutes across a semipermeable membrane. Reverse osmosis is a water purification process that uses a semipermeable membrane to remove ions, molecules and larger particles from water. It is commonly used in desalination and water filtration systems. Diffusion is the movement of molecules from an area of high concentration to an area of low concentration. While diffusion plays a role in processes like the mixing of detergents in water but it is not the main working principle of a washing machine.