Why is the luminous efficiency small for a filament bulb as compared to a mercury vapour lamp ?

The yellow colour has a greater luminous efficiency as compared to the other colours. Can we increase the illuminating power of a white light source by putting a yellow plastic paper around this source ?

The overall luminous efficient of a 100 W electric lamp is 25 lumen W^-1 . Assume that light is emitted by the lamp only in the forward half, and is uniformly distributed in al diredctionsin this half. Calculate the luminous flux falling on a plane object of area 1cm^2 placed at a distance of 50 cm from the lamp and perpendicular to the line joining the lamp and the object.

Explain the following : (a) Why is tungsten used almost exclusively for filament of incandescent lamp ? (b) Why are the conductors of electric heating devices, such as toaster and electric irons, made of an alloy rather than a pure metal ? ( c) Why is the series arrangement not used for domestic circuits ? (d) How does the resistance of a wire vary with its cross-sectional area ? (e ) Why are copper and aluminium wires usually employed for electricity transmission.

Why is it necessary for a pendulum executing SHM to have its amplitude small as compared to its length ?

Why has water higher vapour pressure than mercury ?

The luminous flux of a 1 W sodium vapour lamp is more than that of a 10 kW source of ultraviolet radiation. Comment.

A bulb of constant volume is attached to a manometer tube open at other end as shown in figure. The manometer is filled with a liquid of density (1//3)^("rd") that of mercury. Initially h was 228 cm. Through a small hole in the bulb gas leaked assuming pressure decreases as (dP)/(dt)=-kp. If value of h is 114 cm after 14 minutes, what is the value of k (in "hour"^(-1) )? [ Use : In (4/3) =0.28 and density of Hg =13.6 g/mL.].