## Question

### Solution

Correct option is

104 s–1

The intensity of visible light is 10–10 Wm–2 and the area of the pupil is . Therefore, the light energy entering the pupil is   The average wavelength of visible light is  Let n be the number of photons that must enter the eye second to produce the required energy. Then,     .

Thus, when about 10 thousand photons enter the eye per second, the eye can just see. This is why our eye can never count photons even in barely detactable light.

#### SIMILAR QUESTIONS

Q1

Which one of the following parameters of the emitted X-rays increases when the potential difference between the electrodes of an X-ray tube is increased?

Q2

Calculate the energy of a photon, in electron-volt (eV) and in watt-hour (W h), of wavelength 6600 Å. Q3

An X-rays tube produces a continuous spectrum of radiation with its short wavelength end at 0.45 Å. What is the maximum energy of a photon in the radiation? What is the order of accelerating voltage (for electrons) required in such a tube? Q4

In an accelerator experiment on high-energy collisions of the electrons with positrons, a certain event is interpreted as the annihilation of an electron-positron pair of total energy 10.2 BeV into two -rays of equal energy. Find the wavelength associated with each -ray. Q5

Energy from Sun is received on earth at the rate of . If average wavelength of solar light is taken as 550 nm, then how many photons are received on earth per meter2 per second? Q6

Monochromatic light of frequency is produced by a laser. The power emitted is . What is the energy of a photon in the light beam?

Q7

A beam of green light gives energy at the rate of 1 Js–1 to a surface where it is fully absorbed. How many photons reach the surface per second? If every 100 photons emit one electron, how much current will flow from the surface? Q8

Calculate the number of photons emitted per second by a transmitter of 10 kW power, emitting radio waves of wavelength 500 m. Q9

Calculate the number of photons emitted per second by a transmitter of 10 kW power, emitting radio waves of wavelength 500 m. Q10

A 5-W point-source emits monochromatic light of wavelength 5000 Å. How many photons per second strike a unit area placed 5 m away from the source and illuminated by it? What should be the work function of the metal from whose surface this light can liberate photoelectrons? 