Question

Are these true or false, and explain why please.


White light shines on a sheet of iron but does not cause electrons to be emitted from it. Once the intensity of the white light is increased enough electrons will start to be emitted from the iron sheet.

The Bohr model provides a successful explanation for the emission spectrum of hydrogen gas.

Answer 1

part a ) this is example of photoelectric effect

answer for part a ) is false

When you increase the intensity of light, you are increasing the number of photons in a beam. So more electrons get ejected. ( in case of visible light ....no electrons will be emitted from iron and copper )

part b ) true

Bohr postulated that the electron orbits the proton like a planet orbits the solar system. The centripetal force is provided by electrostatic attraction.

So centripetal force = m v^2 / r = Lv/r^2 = L^2 / mr
=
electrostatic attraction = k e^2 / r^2

Bohr additionally postulated that the angular momentum is quantized:
L = mvr = n h-bar

L v = n hbar v = ke^2
So the available speeds are:
v = ke^2 / (n hbar)

The radii are:
r = mke^2 / (n hbar)^2

And the energy levels are:
E = 1/2 mv^2 - ke^2 / r
= -mk^2e^4 / 2(n hbar)^2

If you make a transition from one energy level to another, you release a photon that carries away the energy difference.

deltaE = hf = mk^2e^4 / 2hbar^2 (1/n1^2 - 1/n2^2)