A spanner has long handle. Why?

A spanner is used to turn a nut to open or tighten it.
The rotational effect depends on the perpendicular distance between the force and the point of application of force. When we increase the perpendicular distance then the Moment of force increases keeping the moment same.

CLOUDS APPEAR WHITE, WHY?

Cloud appears white due to the phenomena of scattering of white light. The water particles in the cloud are big in size as compared to air molecules and wavelength of light. Hence all the colours get scattered in equal intensity and mixture of all colours gives white light. This white light reaches our eyes giving the impression that colour of a cloud is white.

Temperature of surrounding falls after a heavy shower. Why?

Water has high specific heat capacity . It absorbs large amount of heat from the surrounding without  much rise in its temperature .Hence the temperature falls .

WHY IS EARTHING OF AN APPLIANCE DONE?

Earthing is required in a circuit when
1. the appliance draws high current. High power devices draw large current.(Current =power/voltage).
2. the appliance has outer metallic case.

CALORIMETER

It is a device to measure the heat lost or gained by one substance mixed with another at different temperature.
It is based on the principle of mixtures or principle of calorimetry.
Calorimeter is made of thin sheet of copper kept in a wooden jacket to with other insulating materials so that the process exchange heat by conduction is checked. Its surfaces are polished to check the process of radiation. Wooden or asbestos lid is used to minimise the loss of heat by convection.

Thin sheet is used to lower the heat capacity.

Temperature falls as altitude increases, Why?

The volume of rising warm air increases with height due the availability of more space above. This expansion (Joule-Thompson effect) results in cooling effect. Hence hillstations have low temperature. This phenomena helps in the formation of clouds and various forms of precipitation.

FUSE WIRE

Fuse wire is a safety device to limit the current in an electric circuit. It gets melted when excess current flows in a circuit. It works with the principle of heating effect of electric current. It is made with an alloy of lead and tin (solder wire).
Its material has two important properties
1. It has low melting point (around 250 degree celcius).
2.  It has high resistivity.

Sky appears blue, why?

Question: Why does sky appear blue ?
Answer: Sky appears blue due to the scattering of light by air molecules. Blue components (violet, indigo, blue colours) of white light are scattered the most owing to their short wavelengths compared to other colours. This scattered blue light reaches our eyes and the sky appears blue.