Properties of matter questions | form five Physics

Mention any two factors which affect the surface tension of the liquid and in each case explain two typical examples.

Why molecules on the surface of a liquid have more potential energy than those within the liquid? Briefly explain.

Derive an expression for excess pressure inside a soap bubble of radius R and surface tension when the pressures inside and outside the bubble are P₂ and P₁ respectively.

A soap bubble has a diameter of 5mm. Calculate the pressure inside it if the atmospheric pressure is 10⁵ Pa and the surface tension of a soap solution is 2.8x10^-2 Nm^-1.

Water rises up in a glass capillary tube up to a height of 9.0cm while mercury falls down by 3.4cm in the same capillary. Assume angles of contact for water-glass and mercury-glass as 0^o and 135^o respectively. Determine the ratio of surface tensions of mercury and water.

Briefly explain the following observations as applied to strengths of materials:

1. Bridges are declared unsafe after long use.
2. Iron is more elastic than rubber.

A composite wire of diameter 1 cm consists of copper and steel wires of lengths 2.2m and 2m respectively. Total extension of the wire when stretched by a force is 1.2mm. Calculate the force, given that Young`s modulus for copper is 1.1x10¹¹ Pa and for steel is 2x10¹¹ Pa.

What do you understand by the following terms?

1. A perfectly plastic material
2. The Ultimate tensile strength
3. An elastic limit
4. Poisson`s ratio.

Two rods of different materials but of equal cross-sections and lengths 1.0m each are joined to make a rod of length 2.0m. The metal of one rod has coefficient of linear thermal expansion of 10^-5/ ^oC and  Young`s modulus 3x10¹⁰ N/m². The other metal has the values 2x10^-5/ ^oC  and 10¹⁰ N/m² respectively. How much pressure must be applied to the ends of the composite rod to prevent its expansion when the temperature is raised by 100^oC?

A steel rod of length 0.60m and cross-sectional area 2.5x10^-5m² at a temperature of 100^oC is clamped so that when it cools was unable to contract. Find the tension in the rod when it has cooled to 20^oC.