Question

If electrons are ejected from a given metal when irradiated with a 10-W red laser pointer, what will happen when the same metal is irradiated with a 5-W green laser pointer? (a) Electrons will be ejected, (b) electrons will not be ejected, (c) more information is needed to answer this question. Group of answer choices

Answer 1

Answer:

(b) electrons will not be ejected

Explanation:

Determine the number of photons ejected by 10 W red laser pointer.

The wavelength (λ) of red light is  700 nm = 700 x 10⁻⁹ m

Energy of a photon is given as;

$E = \frac{hc}{\lambda}$

where;

h is Planck's constant, = 6.626 x 10⁻³⁴ J/s

c is speed of light, = 3 x 10⁸ m/s

$E = \frac{6.626*10^{-34} *3*10^8}{700 X 10^{-9}} \\\\E = 2.8397 *10^{-19} \ J/photon$

The number of photons emitted by 10 W red laser pointer

10 W = 10 J/s

$Number \ of \ photons = 10(\frac{ J}{s}) * \frac{1}{2.8397*10^{-19}} (\frac{photon}{J} ) = 3.522 *10^{19} \ photons/s$

Determine the number of photons ejected by 5 W red green pointer

The wavelength (λ) of green light is  500 nm = 500 x 10⁻⁹ m

$E = \frac{hc}{\lambda} = \frac{6.626*10^{-34} *3*10^8}{500*10^{-9}} = 3.9756 *10^{-19} \ J/photon$

The number of photons emitted by 5 W green laser pointer

5 W = 5 J/s

$Number \ of \ photons = \frac{5J}{s} *\frac{photon}{3.9756*10^{-19}J} = 1.258 *10^{19} \ Photons/s$

The number of photons emitted by 10 W red laser pointer is greater than the number of photons emitted by 5 W green laser pointer.

Thus, 5 W green laser pointer will not be able to eject electron from the same metal.

The correct option is "(b) electrons will not be ejected"