Two plates identical in size, one of black and rough surface `(B_1)` and the other smooth and polished `(A_2)` are interconnected by a thin horizontal pipe with a mercury pellet at the centre. Two more plates `A_1` (identical to `A_2`) and `B_2` (identical `B_1`) are heated to the same temperature and placed closed to the plates `B_1`, and `A_2` shown in Fig. The mercury pellet

Options

A. moves to the right
B. moves to the left
C. remains stationary
D. starts oscillating left and right

Answer

C

Explanation

Smooth and polished plates are poor radiators of heat. Hence, heat coming out from A is small, even though B being a black and rough plate is a good absorber. Effectively the heat coming to the left of pellet P is small.
Black and rough plates are good radiators of heat. Hence plate `B_2` radiates heat to a satisfactory level , however plate `A_2` being smooth and polisher, is a bad absorber.Effectively the heat coming to the right of P is also small.