# WaPNoL

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- Created by: dkoning00
- Created on: 09-05-17 13:08

What is the amplitude of a wave?

Maximum displacement from the equilibrium position

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And the frequency?

Number of waves passing a point per second (or number of wave oscillations per second).

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Period?

Time for one complete wave oscillation

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Wavelength

Distance between two consecutive points that are in phase (e.g. successive peaks)

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v=

fλ

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What is phase difference?

The fraction of a cycle two waves differ by

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What does in phase mean?

Phase difference = 0°

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What does anti-phase mean?

Phase difference = 180°

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What is a wavefront?

A line on which all the waves are in phase e.g. all the peaks

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Describe a transverse wave

The particles oscillate at right-angles to the direction of energy transfer (propagation)

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Describe a longitudinal wave

The particles oscillate backwards and forwards in the direction of energy transfer (propagation)

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Give an example of each

Transverse - EM radiation (light). Longitudinal - sound

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Give a typical wavelength and use of radio waves

10^2m - TV and radio transmission

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Microwaves

3cm - microwave ovens, mobile phones

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Infrared

10^-6m - thermal imaging, remote controllers

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Visible light

400-700nm - photography, human eyesight

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Ultraviolet

10^-8m - security markings

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X-ray

10^-10m - medical/security scanners

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Gamma

10^-12m - sterilisation, cancer treatment

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What is the speed of light in a vacuum?

3x10^8 m/s

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What is interference?

The combination of two or more waves of the same type

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Describe coherence

Sources are coherent if they maintain a fixed phase relationships

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State the principle of superposition

The resultant displacement of two or more waves at a point is equal to the VECTOR sum of their individual displacements at that point

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What are maxima?

Waves meet with 0° phase difference, causing constructive superposition. This produces a region of maximum amplitude

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What are minima?

Waves meet with 180° phase difference, causing destructive superposition. This produces a region of minimum (not necessarily zero) amplitude

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How is a standing/stationary wave created?

When two identical waves pass through each other in opposite directions

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What are nodes and antinodes?

Nodes - points that don't move/have zero oscillation. Antinodes - points of maximum amplitude with displacement equal to that of the original waves

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Are particles between nodes in phase or out of phase?

In phase (but with different amplitudes)

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What is the phase difference of particles either side of a node?

180°

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Whats the difference betweeen a progressive wave and a standing wave (of the same frequency, amplitude etc)?

Progressive waves transfers energy, standing wave stores it

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What is path difference?

Difference in distance travelled by two waves to a single point

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If the path difference between two waves is an odd multiple of half wavelengths, what is the phase difference at that point?

180° out of phase

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What is transmission?

When wave energy is (partially or completely) carried through, out of or into a media

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What is reflection?

When a wave rebounds off an interface

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Angle of incidence =

Angle of reflection

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What is refraction?

Change in speed of a wave as it passes into a different medium causing a change in wavelength. (Causes bending of the direction of the wave if it is not already moving along the normal)

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What is the Critical Angle?

The angle of incidence that causes an angle of refraction = 90° (i.e. greatest angle of incidence that allows a ray to exit a medium.)

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Give the equation for calculating the critical angle of a media bondary

C = arcsin(n1/n2)

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What is Total Internal Reflection and when does it occur?

Occurs inside a medium when a ray fails to exit (transmit) and reflects back in because the Reflection angle of incidence is greater than the ‘critical angle’

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What is the optical centre of a lens ?

A point in the lens through which rays will pass without deviation

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What is the principle axis?

A line that passes at 90 degrees through a lens' optical centre

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What is the focal length?

Displacement along the principle axis from optical centre of a lens to the real/virtual focal point

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How do you calculate the power of a lens and what are the units?

P = 1/focal length unit dioptre (m^-1)

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Describe how parallel rays pass through a converging lens

Pass through and converge to met at a REAL focal point

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Do converging lenses have negative or positive power and focal length?

Positive

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Describe how parallel rays pass through a diverging lens

Pass through and diverge from a VIRTUAL focal point

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Do diverging lenses have negative or positive power and focal length?

Negative

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Describe the difference between real and virtual images

A real image can be focused and projected, a virtual image is created by the brain at a virtual focal point and cannot be projected

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Give the lens equation and state what each part means

1/u + 1/v = 1/f u = distance parallel to principle axis from object to optical centre v = distance parallel to principle axis from optical centre to image

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How can you find the distance (x) of an object using pulse echo techniques?

x = vt/2 send out waves of a known speed and measure the time taken for them to return

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How can you improve scan resolution?

By shortening the wavelength and pulse time - this reduces diffraction and interference between outgoing and incoming pulses

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What is plane polarisation?

Transverse waves are restricted to oscillate in one plane only and at right angles to the direction of energy transfer

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What is diffraction?

Spreading of a wave through a gap or around an obstacle

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When does maximum diffraction occur?

When the gap width = λ

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Use Huygen's principle to explain why a diffraction pattern occurs with single slit diffraction

When the wave goes through the gap, the edges become wavelet sources which spread out and interfere with each other, thus giving minima and maxima

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What does each part in the single slit diffraction equation, sinθ = λ/a, mean?

θ is angle between central maxima and first minima, λ = wavelength and a = slit width

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What does each part of the diffraction grating equation, nλ=dsinθ, mean?

n = maxima number, θ = corresponding angle that the nth maxima occurs at, λ = wavelength and d = slit separation

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How can you determine the wavelength of a coherent light source?

Use a diffraction grating to get the most number of visible maxima, measure the distance between the maxima and the distance between the grating and the surface to calculate θ, then use the diffraction grating equation to find λ

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Give evidence of electron wave properties

Electrons show diffraction and interference effects when passed through a crystal lattice

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Define intensity and give its units

Power received per unit area Wm^-2

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What is a photon?

A packet of energy carried by each electromagnetic wave

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What property of EM radiation determines the photons' energy? Give the photon energy equation

Frequency E=hf

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Describe what is meant by the statement "a photon's energy is quantised"

It gives up all of its energy at once or not at all

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Give evidence of wave and particle behaviour of EM radiation

Wave - Interference, diffraction and polarisation. Particle - Photoelectric effect, quantised energy of photons

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What is an Electron-Volt?

A more convenient unit for energy than the Joule - 1.6 × 10-19 J

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What is the photoelectric effect?

The release of ‘delocalised’ electrons (from the surface of a metal) by e-m radiation. ONE photon interacts with ONE, instantly giving up all of its energy to ***** the electron

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Give Einstein's photoelectric equation and describe each part

hf = Φ + KE(max)

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What is the Work function (Φ) of a metal?

This is the minimum energy needed to free a ‘delocalised’ electron from the surface of that particular metal

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What is the Threshold frequency?

This is the lowest frequency of e-m radiation needed to match the work-function for a particular metal

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What is stopping voltage?

This is the minimum reverse voltage needed to stop all photoelectrons from flowing

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How can you use stopping voltage to calculate the maximum KE of the photoelectrons?

KEmax = V(stopping voltage) x e (charge of an electron)

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Describe a circuit to determine stopping voltage

A power supply connected to a potentiometer to vary resistance with an ammeter in series and a voltmeter across a photocell. Increase voltage until the ammeter displays 0, this is the stopping voltage

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What is an energy level in an atom?

A unique, discrete amount of energy an electron in an atom can have

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What is the ground state?

The lowest energy state an electron can occupy in an atom

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How do electrons move up energy levels?

If the atom absorbs a photon with energy equal to the difference between a lower and higher energy level, the photon gives up all of its energy and 'excites' the electron to the higher level

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What happens when an electron falls down energy levels?

A photon is emitted with energy equal tot he difference between the higher level and the lower level

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What is an emission spectrum and how is it created?

A set of discrete coloured lines on a black background. Produced when atoms emit a range of photons with specific frequencies

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What is an absorption spectrum and how is it created?

A continuous coloured spectrum with thin black lines showing the missing photons of specific frequencies that have been absorbed to excite electrons

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Why do different elements have different emission and absorption spectra?

Because the differences between energy levels are different in all elements resulting in different frequencies of phtonos being emitted or absorbed

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State the Principle of Complimentarity

Particles (e.g. electrons, photons, etc.) sometimes have the properties of particles and sometimes have the properties of waves, but never both at the same time

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What is the equation λ = h / p used for? What does each part mean?

Used for finding the de Broglie wavelength of a particle with mass (e.g. an electron) λ = de Broglie wavelength, h = Planck's constant, p = particle's momentum

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## Other cards in this set

### Card 2

#### Front

And the frequency?

#### Back

Number of waves passing a point per second (or number of wave oscillations per second).

### Card 3

#### Front

Period?

#### Back

### Card 4

#### Front

Wavelength

#### Back

### Card 5

#### Front

v=

#### Back

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