Atomic

Question 1

explain photoelectric effect

Answer 1

As a photon strikes on the cathode, part of its energy becomes the KE of the emitted photoelectron, some electrons may acquire sufficient energy to overcome the potential barrier between cathode and anode. They reach the anode and a small current flows.

Question 2

what is work function

Answer 2

it is the minimum energy required to remove a photoelectron from the metal

Question 3

postulates of Bohr’s model of the hydrogen atom which are not classical

Answer 3

Constant energy of an electron in its stable orbit without emitting radiation
The electron can occupy certain discrete orbits only.
The angular momentum of the electron is quantized
The atom can only emit or absorb radiation in the form of a photon when it jumps from one energy level to another

Question 4

Why a light pass through the hydrogen gas without absorption

Answer 4

The energy of the light does not match the difference between ground state and other energy levels.

Question 5

not all the electrons emitted can have maximum kinetic energy. Explain.

Answer 5

Only those free electrons on the surface can have the maximum kinetic energy

Question 6

why there is no time delay is observed for electrons to be ejected from the metal surface even though the intensity of light is very weak

Answer 6

it is a one-to-one process that an electron can be ejected instantaneously if it accepts a photon of energy larger than the work function of the metal.

Question 7

There are dark lines in the sun spectrum because light at certain wavelengths emitted by the sun are….

Completely absorbed by the sun atmosphere
or
Partly absorbed by the sun atmosphere?

Answer 7

Partly absorbed by the sun atmosphere

it will release the energy again towards all direction

Question 8

State the result of scattering experiment with a particle and gold foil

Answer 8

Most a particle pass through the coil
Some were only slightly deflected
A small number of a particle were scattered at large angle and a few even rebounded backward

Question 9

why Thomsons model of atom cannot proof the result of scattering experiment

Answer 9

Since the charge and mass of an atom of Thomson atomic model are evenly distributed, the alpha particle should not be deflected.

Question 10

the distance of closest approach of a particle to gold atom is the good estimate of the upper limit of

Answer 10

the radius of a gold nucleus

Question 11

why spectral lines are discrete but not continous

Answer 11

When an atom transits from a higher energy level to a lower one a photon with energy equals to the energy difference between the levels is emitted

Since energy levels are quantized the energy of the photons emitted can take some discrete values

Question 12

is bohrs model only applicable to H atom?

Answer 12

no

all atom with 1 electron

Question 13

will nano size particle have a lower melting point

Answer 13

yes

there is melting pt depression effect

Question 14

why there is not a time delay for photoelectric emission to occur

Answer 14

Light energy is transfered to electrons of cathode in packets or whole number of quanta called photons

Question 15

why not all photoelectrons possess the maximum ke

Answer 15

Electrons not on the surface need an amount f energy more than the work function to escape from the electode

Question 16

when s in s=rveta increase

resolving power increase?

Answer 16

NO

resolving power only depends on veta

Question 17

classical aspect in Bohrs model

Answer 17

the centripetal force is provided by coulomb force
the electron motion obeys Newton’s law of motion
the electron is considered as a particle revolving around the nucleus in definite orbit

Question 18

physical meaning of a hydrogen atom in its ground state

Answer 18

lowest energy level

or most stable state

Question 19

what is rayleigh criterion

Answer 19

two point objects can be just resolved when the central maximum of the diffraction pattern of one object is centred on the first order minimum of diffraction pattern of the other

Question 20

can TEM produce 3D image?

Answer 20

no
it can only produce 2D
while STM can produce both 2D and 3D

Question 21

why there is only discrete line in the emission spectrum

Answer 21

when an electron in a hydrogen atom drops form a high energy level to a lower one , a photon with energy equal to the energy difference between the levels is emitted

since energy level is quantized, energy of the photons emitted can only take some discrete value. This result in discrete spectral lines

Question 22

how to cal the wavelength of photon with an energy given

Answer 22

use E=hc/lambda to think

Question 23

photon mass?

Answer 23

no mass

Question 24

what is meant by ‘the ground state of the atom’

Answer 24

the condition in which every electrons is in its own lowest energy level available

Question 25

what is the significance of the zero energy level

Answer 25

the electron is free from the influence of the atom

Question 26

what is meant by the work function of a metal

Answer 26

the minimum energy for liberating an electron from the surface of a metal

Question 27

why photoelectrons are emitted with different speeds though the energy of each incident photon is fixed

Answer 27

part of the energy gained by an electron from a photon is lost through a number of collisions with the surrounding electrons

Question 28

what activity within an atom gives rise to the emission lines?

Answer 28

Electrons transition from a high energy level to lower one within an excited atom

Question 29

what is the physical significance of the spectrum consisting of discrete lines

Answer 29

energy levels are quantized

Question 30

what is physical significance of the negative sign in -13.6eV

Answer 30

the electrons is bounded

Question 31

what is physical significance of the magnitude of the term -13.6/n^2

Answer 31

the magnitude is the energy of that level with respect to E(infinity)

Question 32

refer to the IV graph, elaborate one observation of the photoelectric effect that cannot be explained by the wave theory

Answer 32

According to the wave theory, the energy of lights depends on its intensity
however the stopping potential is independent of light intensity

Question 33

what is the physical meaning of the terms hf

Answer 33

it is the energy processed by each incident photon