Practice MCQ Questions and answers on Physics-GK

The rise or fall of liquid due to capillarity in a beaker of water depends upon the radius of the bore of the tube (s) which is/are dipped into it. The narrower the bore of the tube, the greater is the rise or fall of the liquid in the tube. So in this case, water will rise in both the glass tube and the glass capillary tube.

Surface tension could be defined as the property of the surface of a liquid that allows it to resist an external force, due to the cohesive nature of the water molecules.

Let M and m grams be the mass of boat + rock in it. By law of floatation(M+m) grams of water will be displaced. This has a volume of (M+m)cc. That means the level of water in pool has risen up by (M+m)cc with the boat + rock when it is floating. If the rocks in the boat are thrown not into the pool but outside, the weight left is only M grams the weight of the boat. This will have displaced M cc of water only i.e less water than in the case of loaded boat. But if the rocks are put in the water in the pool and not outside, then the water in the pool will rise not only by M cc on account of empty boat but also by a volume of the stone put into it. This volume will be m/d where m is the mass of rock and d density of rock.
Now m/d is < m. Thus the total rise will be (M+m/d) which is < M + m.

The oil in the wick of an oil lamp rises up due to capillary action. This effect is due to surface tension of liquids. The wick here acts as a capillary tube.

Fog is tiny water droplets or ice crystals suspended in the air at or near the Earth's surface. Hence, fog is an example of a colloidal system liquid dispersed in gas.

Radius of a capillary tube is inversely proportional to the height of the liquid column. So, if radius of the tube is doubled, rise of level of water will becomes half of the previous rise in capillary tube. Capillary action, or capillarity, is the ability of a liquid to flow in narrow spaces without the assistance of, and in opposition to external forces like gravity. The effect can be seen in the drawing up of liquids between the hairs of a paint-brush, in a thin tube, in porous materials such as paper, in some non-porous materials such as liquefied carbon fiber, or in a cell. It occurs because of inter-molecular attractive forces between the liquid and solid surrounding surfaces.

The pin or needle floats because of an invisible elastic skin on the surface of the water. This elastic skin is called surface tension. Surface tension of the water leads to forces strong enough to support the needle’s weight.

Materials for rain proof coats and tents owe their water proof properties to Surface Tension. The surface of a liquid behaves like an elastic membrane and therefore, has a tendency to contract. This property of liquid is called Surface Tension.

Soap bubble attains spherical shape due to surface tension.

The separation of oil and water is caused due to the difference in surface tension of the two liquids. The water molecules stick together tightly and does not mix with the oil because water molecules are attracted to each other very strongly, forming an invisible “skin” of surface tension around each drop.