Physics
The colour of sky appears blue due to

Dispersion
Refraction
Reflection
Scattering of shorter wave lengths

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Physics
In a bipolar junction transistor

The emitter has the least concentration of impurity
The collector has the least concentration of impurity
All the three regions (the emitter, the base and the collector) have equal concentrations of impurity
The base has the least concentration of impurity

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Physics
It takes much longer to cook food in the hills than in the plains, because

in the hills the atmospheric density is low and therefore a lot of heat is lost to the atmosphere
n the hills the atmospheric pressure is lower than that in the plains and therefore water boils at a temperature lower than 100oC causing an increase in cooking time
due to low atmospheric pressure on the hills, the water boils at a temperature higher than 100oC and therefore water takes longer to boil
in the hills the humidity is high and therefore a lot of heat is absorbed by the atmosphere leaving very little heat for cooking

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Physics
RADAR is used for:

locating geostationary satellites.
detecting and locating the position of objects such as Aeroplanes.
locating submerged submarines.
receiving a signals in a radio receiver.

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