In case of a fire , before the fireman use the water hoses , they shut off the main electrical supply for the area. Explain why they do this.

In case of a fire, before the firemen use the water hoses, they shut off the main electrical supply for the area. Explin why they do this.

Give reason : Water is not used to control fire involving electrical equipment.

Two vessels have the same base area but different shapes. The first vessel takes twice the volume of water that the second vessel requires to fill upto a particular common height. Is the force exerted by the water on the base of the vessel the same in the two cases ? If so, why do the vessels filled with water to thatsame height give different readings on a weighing scale ?

Two charged conducting spheres of radii a and b are connected to each other by a wire. What is the ratio of electric fields at the surfaces of the two spheres? Use the result obtained to explain why charge density on the sharp and pointed ends of a conductor is higher than on its flatter portions.

Two vessels have the same base area but different shapes. the first vessel takes twice the volume of water than the second, vessel requires to fill upto a particular common height. Is the force exerted by water on the base of the vessel the same in the two cases? If so, why do the vessel filled with water to that same height give differnt readings on a weighing scale?

In an experiment to estimate the size of a molecule of oleic acid 1mL of oleic acid is dissolved in 19 mL of alcohol. Then 1 mL of this solution is diluted to 20 mL by adding alcohol. Now 1 drop of this diluted solution is placed on water in a shallow trough. The solution spreads over the surface of water forming one molecule thick layer. Now, lycopodium powder is sprinkled evenly over the film and its diameter is measured. Knowing the volume of the drop and area of the film we can calculate the thickness of the film which will give us the size of oleic acid molecule. Read the passage carefully and answer the following questions : why do we dissolve oleic acid in alcohol ?