Study your flashcards anywhere!

Download the official Cram app for free >

  • Shuffle
    Toggle On
    Toggle Off
  • Alphabetize
    Toggle On
    Toggle Off
  • Front First
    Toggle On
    Toggle Off
  • Both Sides
    Toggle On
    Toggle Off
  • Read
    Toggle On
    Toggle Off
Reading...
Front

How to study your flashcards.

Right/Left arrow keys: Navigate between flashcards.right arrow keyleft arrow key

Up/Down arrow keys: Flip the card between the front and back.down keyup key

H key: Show hint (3rd side).h key

A key: Read text to speech.a key

image

Play button

image

Play button

image

Progress

1/66

Click to flip

66 Cards in this Set

  • Front
  • Back

Describe how infrasound travels through the air.

Air particles oscillate parallel to the direction of propagation




producing compressions & rarefactions

The temperature of a filament lamp increases as the current through it increases. Explain this in terms of the structure of a metal.

Electrons gain kinetic energy as the current increases. (Greater current = greater temperature)


So more frequent collisions of electrons with the lattice ions


lattice ion vibrations increases





Explain the difference between polarised and unpolarised light.

Unpolarised – oscillations/vibrations in many directions




Polarised – oscillations/vibrations in single direction




oscillations/vibrations are perpendicular to direction of propagation

Explain why there is a threshold frequency.

One electrons absorbs one photon




Photon energy: E=hf/E=hv


There is a minimum energy needed for the emission of a (photo)electron


So the emission of electrons only occurs if the frequency of (e.g. light in Q) is higher than the threshold frequency OR




Threshold frequency is the minimum frequency for the emission of photo(electrons)

Explain what is meant by a photon.

(Discrete) quantum/packet of electromagnetic radiation

How set of dark lines are produced

photon absorbed by electron electron moves to higher energy level Or electron excited




where photon energy = difference in energy levels




only certain changes/differences possible between discrete energy levels

Suggest why the energy levels all have a negative value

energy value of level n = ∞ is 0




electrons need to gain energy to move to a higher energy level

How are stationary/standing waves formed?

Waves travelling in opposite/both directions




when the two waves meet they superpose/undergo superposition




producing nodes & antinodes

Define frequency

Number of oscillations/cycles per second

Define wavelength

Distance travelled during one complete oscillation/cycle

State what is meant by critical angle

angle of incidence (for light travelling from denser medium) has angle of refraction of 90 degrees

Refractive index for light passing from air to glass experiment

Measure angles of incidence & refraction




Plot sin i (y-axis) vs sin r (x-axis)




Find gradient









Explain what is meant by plane polarised light.

Reference to oscillations of electric / magnetic field (accept vibrations)




Oscillations/vibrations in one plane only




Plane includes direction of propagation

Explain why the following observations may be understood by using a photon model of light, rather than a wave model.

photon energy depends on frequency Or reference to E = hf (must be link to photons/light)


if photon energy greater than work function, electron emitted (immediately)


whereas for waves energy could build up Or with waves that the electron can absorb energy continuously or over time so any frequency should work

Describe how the ultrasound travels through a metal.

Particles/molecules of metal oscillate




along the direction of propagation/direction of wave travel




Making compressions and rarefactions Or as a longitudinal wave

Explain why pulses are used rather than a continuous wave

Need to measure time at which the echo arrives back


If continuous couldn’t tell when this was Or so pulse must return before next is emitted


so pulse must return


Shorter pulses means smaller thickness can be measured Or longer pulses means only larger thickness can be measured

Sketch the graph of V against I and explain how it may be used to determine İ and r.

Straight line (dependent on first marking point)




V = ε – Ir



Intercept on y axis = ε




Gradient = – r





We usually assume that ammeters have negligible resistance and voltmeters have infinite resistance. The determination of İ and r is not affected by using an ammeter with non-negligible resistance but is affected by using a voltmeter with a low resistance.Explain why.

If ammeter has resistance, current decreased but doesn’t affect the determination because current through cell/r is measured


The resistance of the ammeter contributes to the load/circuit/total resistance


If voltmeter has smaller resistance it would draw current measured current not current through cell/r

Explain why an ammeter




must be placed in series to measure current through a component




must have a very low resistance

current same in series




to ensure the total resistance in the circuit isn’t increased Or to ensure no pd lost




because that would reduce the current being measured

Explain why coherence is necessary to observe the light and dark bands.

coherent = constant phase relationship/difference




The idea that at a given point there would sometimes be constructive interference and sometimes destructive interference etc

Explain what is meant by refraction

change in direction / wavelength (of wave/ray/light/speed?)




when entering an optically denser medium/when entering a medium where the density is different

Describe how a spectral line is produced by a hot gas, explaining why a particular element can only give rise to particular frequencies.

Electrons/atoms move to higher energy levels / get excited


They then move to lower energy levels (accept ground state)


The energy from the move is given out in the form of a photon


The energy levels are discrete Or only certain energy levels are possible


The energy of the photon must be equal to the difference in energy levels Or hf = E2 − E1


There are only a limited number of energy differences and only a corresponding number of frequencies

Suggest why the dolphins emit a series of clicks rather than a continuous sound




OR saying why pulses are more often used/better than continuous

so one returns before one emitted

Talking about emission of photoelectrons




With light (illuminated)




Darkness

photons/light cause emission of (photo)electrons


Idea that (photo) electrons form a current


photon energy greater than or equal to work function


No photons so no photoelectrons released

Define amplitude

Maximum displacement from the equilibrium position

State and explain the effect on the emitted electrons if the frequency of the light is increased

Max kinetic energy/speed/velocity increases/electrons move faster




because Increasing frequency increases energy of photon




E=hf/E=hv





State and explain the effect on the emitted electrons if the intensity of the light is increased.

Number of electrons emitted per second increases/rate of electron emission increases




because there are more photons per second

Difference between p.d. & EMF

Potential difference:




- Electrical energy transferred between 2 points/ P.d. = work/charge




EMF




- Energy (conversion) per unit charge

What is meant by when atoms become excited?

Electrons gain energy




& so move to higher energy levels/states/state above the ground state

Explain how the excited atoms emit radiation.

Electrons move down energy levels




& emit electromagnetic radiation

Explain why only certain frequencies of radiation are emitted

Electrons exist in certain/discrete/specific energy levels




only certain energy changes are possible/ only certain/discrete amounts of energy are released




E=hf/E=hv

Suggest why ____ emits different wavelengths than _____

______ has different energy level spacings than ______




OR different elements have different energy level spacings

Ultrasound PULSES example:




Explain how ultrasound pulses can be used to build up the image of the fetus in the uterus.

Many/large number of pulses




(Ultrasound) travels as pulses so that one pulse is detected before the next pulse is sent.




Time for (echo/reflected) pulse to return measured





Define diffraction

Diffraction is the spreading out of a wave




as it passes through a gap/slit OR




as it passes around an obstacle

State the principle of superposition of waves.

When two or more waves meet




the total displacement at a point is the sum of the individual displacements

Define critical angle

The angle of incidence (in the denser medium) for which angle of refraction is 90º

Describe the difference between a transverse wave and a longitudinal wave.

Transverse waves oscillate perpendicular to the direction of the wave/direction of propagation/energy travel




Whereas




Longitudinal waves oscillate parallel to the direction of the wave/direction of propagation/energy travel

How stationary/standing waves are formed

2 waves of the same frequency/wavelength travelling in opposite directions


superpose/undergo superposition


nodes & antinodes produced


OR


where in phase, constructive interference/antinodes


where in antiphase, destructive interference/nodes





Define polarised light

when the oscillations (associated with the wave) travel in one direction only






OR you could describe it as a transverse wave as only transverse waves can be polarised

How to measure angle of rotation for plane polarisation

Mention of polarising filter/Polaroid/polariser


Rotation (of filter) until minimum/ maximum intensity (notrotation of solution)


(Rotation) done with and without the sugar solution


identifies correct difference in angles


use of protractor/polarimeter

)In a demonstration, ultraviolet light is incident on a zinc plate and electrons are emitted. The intensity of the ultraviolet light is increased. Explain the following observations:




• the number of electrons emitted per second increases




• the maximum kinetic energy of an electron does not change.

Mention of photons OR photoelectric (NOT photoelectrons)


• Idea of one to one relationship from photon to electron


• Intensity of light relates to number of photons/sec


wavelength/frequency is constant • photon energy depends on frequency /reference to E=hf




• Reference to hf = Φ + ଵଶmv௠௔௫ଶ and Φ constant

e.g. Explain why the metal plate is made of caesium rather than zinc.

Zinc requires higher frequency /Zinc requires UV/UV dangerous (for students)




Caesium works with visible light

Dopper effect

Moving towards:


Higher frequency/pitch


So therefore wavelengths are shorter




Moving away:


Lower frequency/pitch


So therefore wavelengths increases/spread out




TALK ABOUT CHANGE IN FREQUENCY ALSO

Define energy level

Energy an electron can have/Discrete energy of an electron

Define wavefront

Line/surface joining points in phase

Define displacement

The distance any part of the wave has moved from its rest position

Define nodes

No displacement


0 amplitude


Destructive interference links with nodes


Where 2 waves cancel out/


2 waves exactly out of phase


Waves with more nodes represent higher energies because:


More nodes = higher frequency & shorter wavelengths, momentum larger, E=hf



Define antinodes

Position of maximum amplitude


OR




Position where waves are (always) in phase




So constructive interference links with antinodes

Define monochromatic

Single wavelength/frequency/colour

Total internal reflection

When the angle of incidence is greater than the critical angle




i > c

Refractive index

(of a material) is a measure of the change in speed of light as it passes from a vacuum (or air as an approximation) into the material

Difference between plane polarised light & unpolarised light

Plane polarised - Oscillations are in one plane only which travel perpendicular to the direction of the wave/direction of propagation




Unpolarised - Oscillations may occur in more than one plan

Why transverse waves can be polarised but longitudinal waves cannot

Transverse waves oscillate perpendicular to the direction of the wave/direction of propagation


So in transverse waves, oscillations can be in different planes


but polarisation restricts it to only one plane


Longitudinal waves however oscillate parallel to the direction of the wave/direction of propagation so it already oscillates in one plane (only)?

Why does the ideal voltmeter have infinite resistance?

So that the current through the voltmeter is 0/negligible/




So it doesn't reduce the resistance of the circuit




Or reduce the p.d. it is meant to be measuring

Photon model rather than wave model




TALKING ABOUT EMISSION OF ELECTRONS FROM THE SURFACE OF A METAL

Electrons in atoms can only occupy certain discrete energy levels


ground state = lowest energy level an electron can occupy


energy is transferred in the collisions


electrons can move/jump to higher energy levels & become excited when they gain energy




These electrons return later back down to the ground state by emitting energy in the form of photons




photons have a specific energy or and frequency




E=hf/E=hv

Define internal resistance

Resistance of a battery or cell

I = nqvA

I = Electric current/A


n = Number of charge carriers per unit volume/m^-3


q = Charge carried by each carrier/C


v = Drift velocity which is the average velocity of the electrons/chargecarriers / ms^-1


A = Cross-sectional area / m^2





Define

Quantum - A discrete/indivisible quantity




Particle - Photon/electron


Photoelectron - Electrons released by the interaction with a photon. 1 photon releases 1 electron


electronvolt, eV - The amount of energy needed to move 1 electron through a potential difference of 1 volt

Define threshold frequency

Minimum frequency of radiation that will produce a photoelectric effect. +


Cause electrons to be emitted as photoelectrons


Threshold frequency is needed because:


- Electrons require a certain amount of energy to escape from a surface


This energy comes from 1 photon of light


E=hf



Define work function

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

Why it supports the particle theory but not the wave theory of light:

Particle theory:


-E=hf/E=hv


-Increased frequency means more energy of a photon


-Increased frequency = greater energy of photon = greater kinetic energy of the electrons


-1 photon releases 1 electron


More intense light means more photons therefore more electrons





Conditions for (observable) interference

- Same type of wave




- (Approx) same amplitude/intensity




- Same frequency/OR wavelength




- Coherent, so constant phase relationship/difference?

Define potential divider

A type of circuit containing 2 components designed to divide up the p.d. in proportion to the resistance of the components

I =nqvA

If R increases due to stretching:- Current will decrease- I = nqvA- Drift velocity v decreases-nAe constant




If R decreases:- Current will increase- I = nqvA- Drift velocity v increases- nAe constant

EXTRA

-Frequency has no effect on the number of electrons emitted-




-Greater light intensity = more photons = greater number of electrons emitted (as photoelectrons)

Wave theory

Wave theory:


-Wave energy depends on intensity-More intense light = greater kinetic energy of the electrons-Energy is spread over the whole wave-If exposed for long photons are eventually released- For a particular frequency of light. the energy carried is proportional to the intensity