Physics - Study Mode

[#386] A falling drop of rain water acquires the spherical shape due to
Correct Answer

(B) Surface Tension

Explanation

Solution: Raindrops start out as round high in the atmosphere as water collects on dust and smoke particles in clouds. But as raindrops fall, they lose their rounded shape. A raindrop falling through the atmosphere forms as a roughly spherical structure due to the surface tension of water. This surface tension is the “skin” of a body of water that makes the molecules stick together. The cause is the weak hydrogen bonds that occur between water molecules. On smaller raindrops, the surface tension is stronger than in larger drops. The reason is the flow of air around the drop. Air flow on the bottom of the water drop is greater than the airflow at the top.

[#387] Why the needle of iron swims on water surface when it is kept gently ?
Correct Answer

(C) Due to surface tension

Explanation

Solution: According to Archimedes principle and we can note that the amount of water displaced by a needle is lesser than the amount of water moved out by the needle (that is displacement of the needle). So the needle initially stays on the surface of the water and then sinks into the water. Surface tension is a contractive tendency of the surface of a liquid that allows it to resist an external force. It is revealed, for example, in the floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects (e.g. water striders) to run on the water surface. This property is caused by cohesion of similar molecules, and is responsible for many of the behaviors of liquids.

[#388] Rise of oil a wick is due to
Correct Answer

(C) Surface tension of the oil

Explanation

Solution: The phenomenon of rise or fall of liquid in a capillary tube is called capillarity. Oil rises through a wick due to capillarity. The narrow pores in the threads of a wick act like tiny capillaries, through which oil rises. Capillary action is the result of adhesion and surface tension.

[#389] Bubbles of air rise up through liquids due to
Correct Answer

(B) Viscosity and buoyancy

Explanation

Solution: Bubbles of air rise up through liquids due to viscosity and buoyancy.

[#390] Which sources produce alternating current (AC)?
Correct Answer

(B) Hydro-electric generators

Explanation

Solution: The sources are hydroelectric power plants, thermal power generators,nuclear power generators, AC generators.