waves Nature of light

Question 1

definition of wavelength

Answer 1

Distance between a point and the next point that motion is repeated m

Question 2

definition of frequency

Answer 2

Number of waves generated moving past a point per second in hz

Question 3

what is the wave front

Answer 3

a surface which is used to represent the points of the wave which is in phase

Question 4

What is reflection

Answer 4

the throwing back of a wave from a surface

Question 5

what is refraction?

Answer 5

the change in direction of a wave as it enters a new medium and changes speed

Question 6

when is a diffraction the most effective

Answer 6

when the wavelength is similar to the slit.

Question 7

Diffraction definition

Answer 7

diffraction, the spreading of waves around obstacles

Question 8

what happens to the amplitude of a wave as it diffracts

Answer 8

it decreases which also means its energy decreases.

Question 9

What is diffraction

Answer 9

the spreading out of a wave as it passes through a gap

Question 10

What criteria must be met for maximum diffraction to occur

Answer 10

the size of the gap must be of the same magnitude as the wavelength of the wave

Question 11

What happens if the gap is much smaller than the wavelength of the wave

Answer 11

The wave will be reflected

Question 12

The diffraction grating equation

Answer 12

n lamba = d sinO

Question 13

What does electron diffraction provide evidence for

Answer 13

The wave nature of electrons. It suggests that particles can demonstrate wavelike properties

Question 14

Diffraction pattern produced by electrons

Answer 14

Concentric circles or bright and dark fringes from a central bright point

Question 15

What pattern should it have if it was a particle

Answer 15

The electron would be unaffected by the gap and pass straight through. A single bright region would be formed.

Question 16

What is the name given to the wavelength of a particle

Answer 16

de broglie wavelength

Question 17

What two factors does the de broglie wl depend on

Answer 17

mass and velocity

Question 18

de broglie wave length equation

Answer 18

lamba = h/mv ( momentum) h is Planks Constant

Question 19

what can mv be replaced with in the de broglie equation?

Answer 19

p Momentum

Question 20

What is the basic process of a pulse-echo technique

Answer 20

• a wave pulse is emitted
  -it is transmitted and reflected at the boundary between two media
• the returning wave (echo) is detected
• The speed and time taken are used to calculate the distance to the object

Question 21

suggest two things that may limit the amount of information that can be obtained by a pulse echo technique

Answer 21

1. the wavelength of the radiation
2. the duration of the pulse

Question 22

What are the two models that can be used to describe em radiation

Answer 22

Particle
wave

Question 23

What model does the photoelectric effect provide evidence for

Answer 23

The Particle model

Question 24

Outline the photo electric effect

Answer 24

• light is shone on a metal plate
  -if the light has a high enough frequency, electrons are emitted from the metal surface
• if the frequency is too low, no electrons are emitted

Question 25

what are the particles of light used to explain the photoelectric effect called

Answer 25

Photons

Question 26

How do you calculate the energy of a photon

Answer 26

e=hf
h is planks constant
f is the frequency of light

Question 27

Explain how a photon can liberate an electron

Answer 27

one photon interacts with one electron and transfers all its energy to it. If this energy is greater than the metals work function, the electron will have sufficient energy to be released.

Question 28

What is the threshold frequency

Answer 28

a metals threshold frequency is the minimum frequency that a photon requires to liberate an electron from its surface

Question 29

If the intensity of light being shone on a metal increases, how does the energy of photoelectrons change

Answer 29

The energy remains unaffected. An increase in intensity means more photons per area and so more photoelectrons are emitted

Question 30

Why are photoelectrons emitted with a range of kinetic energies

Answer 30

the electrons are at different depths in the metal and so require different amounts of energy to be liberated. The excess energy from a photon once an electron has been liberated is the ke of the electron

Question 31

the equation for the maximum ke of a photoelectron

Answer 31

0.5 mv ^2 max- hf -O (work junction)

Question 32

What is the conversion factor between eV and J

Answer 32

1 ev = 1.6x10^-19 J

Question 33

What happens when electrons transition between energy levels

Answer 33

• if electrons move to a higher energy level, radiation must be absorbed
• if electrons move to a lower energy level, Radiation is emitted

Question 34

why can only certain frequencies of radiation be absorbed by an atom to cause an electron transition?

Answer 34

The electrons can only exist in discrete energy levels. The energy of the photon absorbed must be the exact amount of energy required to cover the difference between two discrete energy levels.