3.2.2.2-3 - Collisions Of Electrons And Energy Levels And Photon Emission

Question 1

Where can atoms only exist?

Answer 1

In certain energy levels.

Question 2

How can electrons move down energy levels?

Answer 2

By emitting a photon.

Question 3

Energy gained by electron (eV) =

Answer 3

Accelerating voltage (V)

Question 4

1ev =

Answer 4

1.6x10^-19J

Question 5

What is the energy carried by each photon equal to?

Answer 5

The difference in energies between the levels.

Question 6

hf=

Answer 6

E2 - E1

Question 7

How can electrons move up energy levels?

Answer 7

If they absorb a photon with the exact energy difference between the two levels.

Question 8

What is excitation?

Answer 8

An electron is at a higher level than the ground state.

Question 9

When do we say an atom is ionised?

Answer 9

If an electron is removed from an atom.

Question 10

What is ionisation energy?

Answer 10

The amount of energy needed to completely remove an electron from the atom from the ground state.

Question 11

How do mercury atoms become excited in a fluorescent tube?

Answer 11

Electrons flow through the tube and collide with mercury atoms raising the electrons to a higher level.

Question 12

How are mercury atoms excited to higher energy levels?

Answer 12

The flow of free electrons collides with electrons in other mercury atoms.

Question 13

What happens when these excited electrons return to their ground states?

Answer 13

They emit photons in the UV range.

Question 14

What is the purpose of the coating on the inside surface of the glass in a fluorescent tube?

Answer 14

Photons emitted from mercury atoms are in the ultraviolet spectrum. These photons are absorbed by the powder coating and the powder coating emits photons in the visible spectrum.

Question 15

How is visible light produced?

Answer 15

The electrons cascade down the energy levels, emitting many lower energy photons in the form of visible light.

Question 16

What is a line spectrum seen as?

Answer 16

A series of bright lines against a black background.

Question 17

In the line spectrum what does each line correspond to?

Answer 17

A particular wavelength of light emitted by the source.

Question 18

What do hot things emit?

Answer 18

A continuous spectrum in the visible and infrared.

Question 19

Why are all wavelengths allowed in the continuous spectra?

Answer 19

The electrons are not confined to energy levels in the object product the continuous spectrum.

Question 20

What do you get when light with a continuous spectrum of energy passes through a cool gas?

Answer 20

A line absorption spectrum.

Question 21

Where will electrons be at low temperatures?

Answer 21

In their ground states.

Question 22

What do the photons have to be in order to be absorbed by the electrons?

Answer 22

The photons have to have energies equal to the difference between two energy levels.