1)Books always wrote that "Water is kept warm in shiny kettle as
shiny surface is poor radiator of heat". But why
can't we use "absorber"? Isn't it absorbing more important?
Absorber and radiator are basically the same thing. When the
heat is higher than surroundings, the object can only radiate heat.
When the heat is lower than surroundings, the object can only
absorb heat. There's no two ways about this.
So to keep water warm, a good "absorber" will actually become a
good radiator of heat and radiate the warmth away from the
water.
2)Can we say that poor conductors will be poor absorbers and
good conductors will be good absorbers?
You mean electrical conductors vs heat conductors right? Usually
yes, especially for metals. That's because metal has free electrons
which can help conduct heat rapidly from one end to the other.
I encounter one quriky question from assessment books . They
say" Cold water is place in two containers one made up of metal and
the other plastic" and ask "which water in the container will
increase it temperature more". Is there anything wrong with the
question? I don't understand why the materials concerning
conduction is asked for radiation.
Is that the full question or partial question? Any pictures to
go along?