Explain how the loss of heat (or transfer of heat) due to modes of transfer of heat is 1. Explain how the las minimised in a thermos flask.

Explanation

Transfer of heat is thermos is minimised as under
By conduction: As in conduction heat can transfer by contact of material medium. In thermos air is evacuated between the walls so heat transfer in stopped by conduction mode.
(ii) By convection: As convection mode also require material (fluid) medium and there is nothing between the walls of thermos so heat does not transfer by connection mode. day
(iii) By Radiation: As Ag polish is coated opaque on inner and outer walls of thermos radiation obeys the laws of refraction and reflection so no refraction takes place through opaque wall. Reflection of outer radiation goes outside of innerwall goes inside. So the transfer of heat is minimised by polishing.
(ii) (a) The element present in a group have the same valency.
(b) The element present in a group have identical chemical properties.
(c) The physical properties of the elements in the group vary gradually.
(d) The atomic radii of the elements present in a group increases downwards