Advertisements
Advertisements
Question
A 150 W lamp emits light of the mean wavelength of 5500 Å. If the efficiency is 12%, find out the number of photons emitted by the lamp in one second.
Advertisements
Solution
P = 150 W
λ = 5500 × 10−10 m
Efficiency = 12%
N = `("P"λ)/"hc"`
= `(150 xx 5500 xx 10^-10)/(6.626 xx 10^-34 xx 3 xx 10^8)`
= `(825 xx 10^-7)/(19.878 xx 10^-26)`
= 41.5 × 1019
Number of photons emitted is with 12% efficiency = `41.5 xx 10^19 xx 12/100`
N = 4.98 × 1019
APPEARS IN
RELATED QUESTIONS
Find the (a) maximum frequency and (b) minimum wavelength of X-rays produced by 30 kV electrons.
Why should gases be insulators at ordinary pressures and start conducting at very low pressures?
How does one explain the emission of electrons from a photosensitive surface with the help of Einstein's photoelectric equation?
A diode value is connected to a battery and a load resistance. The filament is heated, so that a constant current is obtained in the circuit. As the cathode continuously emits electrons, does it become more and more positively charged?
The constant A in the Richardson−Dushman equation for tungsten is 60 × 104 A m−2K−2. The work function of tungsten is 4.5 eV. A tungsten cathode with a surface area 2.0 × 10−5 m2 is heated by a 24 W electric heater. In steady state, the heat radiated by the heater and the cathode equals the energy input by the heater and the temperature becomes constant. Assuming that the cathode radiates like a blackbody, calculate the saturation current due to thermions. Take Stefan's Constant = 6 × 10−8 W m−2 K−1. Assume that the thermions take only a small fraction of the heat supplied.
The wave associated with a moving particle of mass 3 × 10–6 g has the same wavelength as an electron moving with a velocity 6 × 106 ms–1. The velocity of the particle is
If a light of wavelength 330 nm is incident on a metal with work function 3.55 eV, the electrons are emitted. Then the wavelength of the wave associated with the emitted electron is (Take h = 6.6 × 10–34 Js)
Emission of electrons by the absorption of heat energy is called ____________ emission.
In which case is electron emission from a metal not known?
Give an example each of a metal from which photoelectric emission takes place when irradiated by
- UV light
- visible light.
