waves

Question 1

what is frequency?

Answer 1

the rate of complete oscillations

Question 2

what is amplitude?

Answer 2

the max displacement from the equilibrium position

Question 3

what is the wavelength ?

Answer 3

the length of one full oscillation

Question 4

what is path difference?

Answer 4

the difference in distance travelled of two waves

Question 5

what is a wavefront?

Answer 5

the surface which is used to represent the points where the phase is the same

Question 6

what is phase?

Answer 6

the position of a certain point on a wave cycle

Question 7

what is coherence ?

Answer 7

when two waves have the same f, same wavelength and a fixed phase difference

Question 8

what is superposition ?

Answer 8

when two waves interact, and their amplitudes are either added or subtracted from each other

Question 9

what is constructive interference?

Answer 9

when two waves meet and their displacements are added

Question 10

what destructive interference?

Answer 10

when two waves meet and their displacements are subtracted

Question 11

how are stationary waves formed?

Answer 11

stationary waves are formed from the superposition of two progressive waves, travelling in opposite directions, with the same f, same wavelength and same amplitude

Question 12

what are nodes

Answer 12

the stationary points on a stationary wave, 0 = amplitude

Question 13

what happens when a wave is polarised?

Answer 13

A polarised wave can only move in one plane, vertically or horizontally, only transverse waves can be polarised

Question 14

what is diffraction

Answer 14

the spreading out of waves when they pass through or around a gap

Question 15

what does huygens’ construction state

Answer 15

every point on a wavefront is a source of wavelets

Question 16

when is diffraction greatest?

Answer 16

when the wavelength of the wave is closest to the gap it is passing through

Question 17

how do you find the amount of slits,d?

Answer 17

the distance between the slits divided by 1, it has to be in m

Question 18

how can electron diffraction be used as evidence of the wave nature of electrons?

Answer 18

-An electron gun accelerates electrons through a vacuum to a crystal lattice.
-Here they interact with small gaps between atoms
-This forms a pattern on a screen behind the crystal

Question 19

what is an interface?

Answer 19

where two materials meet

Question 20

how to waves behave at an interface?

Answer 20

the wave could be transmitted, this is where it passes to the next material, and it experiences refraction
the wave could also be reflected, where it bounces off without moving into the next material

Question 21

what is the pulse echo technique ?

Answer 21

This is where ultrasound (US) waves are reflected when they meet boundaries and different materials.

Question 22

How is the pulse echo technique used?

Answer 22

-Short pulse US waves are transmitted into the target
-It travels until it reaches a boundary between two mediums, where some is reflected back
-The waves are detected
-The intensities of the detected waves are used to determine the structure, the time taken to be reflected is used to determine distance

Question 23

what is photoelectricity?

Answer 23

when photoelectrons are emitted from the surface of a metal when light above a certain frequency is shone on it. This occurs due to electrons absorbing a photon and gaining enough energy to be liberated

Question 24

what is threshold frequency?

Answer 24

the minimum frequency of light required to emit photoelectrons

Question 25

what is the work function

Answer 25

minimum energy required for electrons to be emitted from the surface of a metal

Question 26

what does increased intensity do to photoelectron releaese?

Answer 26

It doesn’t change the rate of increase but does change the magnitude.

Question 27

What does increased exposure of light do to photoelectron release?

Answer 27

It does nothing. Photon energy is transmitted immediately

Question 28

Why does electrons deeper in the metal lose energy?

Answer 28

This is due to collisions between other particles as it leaves the metal

Question 29

how do electron and photon interactions to make photoelectrons work, how can you increase the amount emitted?

Answer 29

It is a one-to-one interaction.
Prolonged exposure does nothing because the interaction is immediate.
There is a threshold frequency (work function) to emit a photoelectron.
Increases intensity increases the rate of release of photons.

Question 30

What is the atomic line spectra and how does it work?

Answer 30

The lines are specific wavelengths of discrete packets of electrons.
Electrons are accelerated in a fluorescent tube, this excites and de-excites an atom which releases a photon. The energies of the photons released correspond to certain wavelengths showing that electrons exist in discrete packets