Figure 1 below shows a cross –section of a vacuum flask.
(i) Name the parts labeled A and B
(ii) Explain how the heat losses are minimized when hot liquid is poured into the flask.
(iii) Boiling water is poured into two identical vacuum flasks A and B. flask A is partially filled while B is completely filled. Both
are closed tightly. State with reasons the flask in which the water is likely to have a higher temperature eight hours later.
Answer:
i) - A. Vacuum
- B. silvered shiny walls
ii)
Heat loss
- By evaporation is minimized by cork
- Through radiation is minimized by silvered walls.
- Through conduction is minimized by double walls.
iii)
- Temperature is likely to be higher in flask B, since some heat is lost by flask A. The air above the water forms convection currents.
- B. silvered shiny walls
ii)
Heat loss
- By evaporation is minimized by cork
- Through radiation is minimized by silvered walls.
- Through conduction is minimized by double walls.
iii)
- Temperature is likely to be higher in flask B, since some heat is lost by flask A. The air above the water forms convection currents.
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The control grids in a Cathode Ray Oscilloscope (CRO) is used to control the brightness of the beam on the screen. How is this achieved? 
