Nature Of Light

Question 0

Define a line spectrum

Answer 0

Discrete lines each typical of the element concerned

Question 1

Does line spectra consist of a continuous band of different colours? What does it if not?

Answer 1

No

Discrete separate lines

Question 2

How do you observe line spectra in the laboratory?

Answer 2

By viewing a discharge tube with a diffraction grating

Gas discharge lamp through a diffraction grating

Question 3

How does the diffraction grating allow the spectrum to be viewed?

Answer 3

A voltage is applied across sodium for example which would vaporise; the hot vapors emit light and the diffraction grating allows it to be viewed

Question 4

How are line spectra observed

Answer 4

By viewing a discharge tube with a diffraction grating

Question 5

Change in E =

Answer 5

Hf

Question 6

How do you convert from eV to J

Answer 6

X1.6x10^-19

Question 7

How is an emission line spectra produced

Answer 7

By a hot gaseous element

Question 8

What happens to electrons at higher temperatures

Answer 8

They’re excited into higher energy levels

Question 9

Is energy emitted or absorbed when going from a high to a low energy level

Answer 9

Emitted

Question 10

What is the difference between an emission and absorption spectrum

Answer 10

An absorption spectrum has black lines on a coloured background where as an emission spectrum his coloured lines on a black background

Question 11

What do you see in an absorption spectrum (in terms of vapor and light)

Answer 11

When white light passes through a cooler water vapor

Question 12

What has the absorption spectrum been used for in our universe

Answer 12

Looking at the composition of distant stars (their elements)

Question 13

How are elements determined on different stars?

Answer 13

Using the absorption spectrum where
the white light passes through the cooler vapours of the outer layers of the star and the positions of the dark lines are compared to the absorption spectra of elements we know on earth

Question 14

How can we check what an element is on a distant star?

How can we be sure?

Answer 14

Use the absorption spectra of the star from white light going through the cooler vapours on the outer layer of the star then comparing the spectrum to that of known elements on earth; the absorption spectra of an element is the same universally

Question 15

What is redshift and what does it suggest/show?

Answer 15

Redshift is the spectral lines of light shifting to lower frequencies (red light) which suggests the source is moving away from us in support of the Big Bang theory as the origin of the universe.

Question 16

What happens to the energy when an electron moves up or down in energy levels
How could we calculate this energy value

Answer 16

It is emitted as a photon

Using E=hf

Question 17

What direction do the electrons move in an emission spectrum

Answer 17

Down energy levels towards the ground state

Question 18

What is the Bohr radius

Answer 18

The shortest radius of the closest possible orbit of an electron around a nucleus

Question 19

What is the de Broglie wavelength equation

Answer 19

Wavelength=h/p

Question 20

What does the de Broglie wavelength suggest

Answer 20

That electrons behave as waves as well as particles

Question 21

What does a stationary wave have to have, to occupy Bohr orbits
Why?

Answer 21

Waves with whole numbers of wavelengths because they’re stable and odd ones are not

Question 22

Why must the waves be standing for the Bohr orbits to exist

Answer 22

Because otherwise the waves wouldn’t be stable and would give out there energy and consequently cease to exist

Question 23

E=hc/?

Answer 23

Hc/wavelength

Question 24

What happens to an unstable electron or wave at higher energy levels

Answer 24

It returns to it's lowest possible energy level and the energy difference is radiated away as a photon

Question 25

How is a photon emitted from an atom

Answer 25

When an electron moves from a higher to a lower energy level

Question 26

How is a photon absorbed

Answer 26

When an electron moves from a lower to a higher energy level

Question 27

How can you calculate the wavelength of a photon when knowing it's energy difference only

Answer 27

Wavelength=hc/E

Question 28

What is the photoelectric effect proving

Answer 28

That light can behave as a stream of particles as well as a wave I.e. Wave particle duality

Question 29

How do you find the photon energy

Answer 29

E=hf

Question 30

What is the work function

Answer 30

The minimum amount of energy required for an electron to escape the surface

Question 31

Energy delivered by a photon goes where

Answer 31

To electrons to get then to the surface and to get then too escape

Question 32

Where does the kinetic energy of an escaped photoelectron come from

Answer 32

It is left over from the energy transferred from a photon to the electron to get it to the surface and escape

Question 33

The speed of an escaping electron depends on how much of their energy is used to get to the surface, what will be the fastest electrons then and what equation can we obtain from this?

Answer 33

The surface electrons because the energy needed to get them to the surface is zero hf=W + Ekmax

Question 34

What is the threshold frequency

Answer 34

Where the energy of the photon is not great enough to cause an emission of an electron from the surface of a metal

Question 35

What happens above and below the threshold frequency

Answer 35

Above=electrons are emitted | Below=electrons aren't emitted

Question 36

What is the x intercept of a max KE/frequency graph equal to

Answer 36

The threshold frequency

Question 37

Qvstop=

Answer 37

KE max

Question 38

Can the ground state lose energy

Answer 38

No