Infrared lamps are used in restaurants to keep the food warm. The infrared radiation is strongly absorbed by water, raising its temperature and that of the food. If the wavelength of infrared radiationis assumed to be `1500` nm, and the number of quanta of infrared radiation produced per second by an infrared lamp (that consumes enregy at the rate of `100` W and is `12%` effcient only) is `(x xx10^(19)`, then the value of x is :
`(Given: h= 6.665xx10^(-34)J-s)`

Options

A. 6
B. 7
C. 8
D. 9

Answer

4

Explanation

Power`=(En ergy)/(time)=((n)/(t))(hc)/(lambda)`
`100xx(12)/(100)=((n)/(t))xx(6.6xx10^(-34)xx3xx10^(8))/(1500xx10^(-9))`
So, `((n)/(t))=no`. of photons per second `=9xx10^(19)`