Revision notes for AS physics (G482), covers electricity, waves and quantum

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  • Created on: 01-06-16 15:33
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Current:
- Flow of charge per unit time
o Electrons in metals, ions in electrolyte
- Conventional current ­ a model used to describe the movement of charge in a circuit (positive to
negative)
- Electron flow ­ the movement of electrons around a circuit (negative to positive)
- One Ampere ­ one Coulomb per second
- Ammeter ­ instrument to measure current
o Connected in series and has negligible resistance to avoid current being affected
Charge:
- One Coulomb ­ charge supplied by one Ampere in one second
- Elementary charge = e- = 1.6x10-19
Kirchoff's Laws:
- First law ­ the sum of current into a junction is equal to the sum of the current
out of that junction
o Conservation of charge
- Second law ­ the sum of e.m.f. is equal to the sum of p.d. around a closed loop in a circuit
o Conservation of energy (E = IR1 + IR2)
Mean Drift Velocity:
- Average speed of charged particles along the
length of a conductor
Conductors:
- Conductor ­ material with high number density (n) of conduction electrons and therefore low
resistance
o Small drift velocity for high current
- Semiconductor ­ material with low number density (n) of conduction electrons and therefore high
resistance
o Higher drift velocity required for current equal to that of a conductor
- Insulator ­ material with negligible number density (n) of conduction electrons and therefore very
high resistance
o No charge carriers therefore n = 0

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Number densities ­ if low electrons have more space to move and collide with each other less
resulting in higher drift velocities
Potential Difference (p.d.):
- Energy transferred per unit charge, when electrical energy is converted to another type
- One Volt = one Joule per Coulomb
- Voltmeter - A device for measuring p.d and e.m.…read more

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Experiment to determine I/V characteristics:
- Vary current and p.d. using variable resistor
- Record current and p.d. from ammeter and voltmeter
- Plot I/V graph
- Resistance = gradient-1
Light Emitting Diodes (LEDs):
- Only allow current to flow in one direction and emit light when
a p.d. is applied across it
- Benefits:
o Turn on instantly
o Emit strong sources of light
o Very versatile
o Operate on low p.…read more

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Negative Temperature Coefficient (NTC) as is for semiconductors:
- A thermistor has a NTC ­ when heated electrons in the thermistor gain enough energy to escape the
metal lattice
- This increases the number of charge carriers available (increasing n) which causes a fall in resistance
- Light dependent resistors (LDRs) work in the same way except increases light intensity causes
electrons to be freed
- I/V for NTC components curves in the opposite direction to that of a filament lamp which has a PTC…read more

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Advantages :
o If a continuous record of temperature or light intensity is needed, you can connect a data
logger to the thermistor or LDR because they produce electrical outputs
o eliminate the chance of human error in the calculations
o Can plot accurate graphs straight away
o Very good at processing collected data
Wave Terminology:
- X = Displacement ­ distance from given point to equilibrium position
- A = Amplitude ­ maximum displacement
- = Wavelength ­ smallest distance between a point on…read more

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Progressive wave:
- A wave that transfers energy from one place to another
- Wave speed ­ the speed at which energy is transmitted by a wave v = f
Refraction:
- Change in direction of a wave as it crosses an interface between two
materials where its speed changes
Polarised wave:
- A wave that oscillates in one direction only
Diffraction:
- The spreading of a wave when it passes through a gap or past the edge of
an object
Electromagnetic waves:
- Travel…read more

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Ultraviolet:
- All can damage the eyes
- UV-A
o 99% of UV, causes tanning and wrinkles
- UV-B
o Can cause DNA in skin to become damaged causing skin cancer
- UV-C
o Absorbed by the ozone layer
Polarisation of waves:
- If a transverse wave is incident on a polariser, oscillations perpendicular to the motion are restricted
to 1 plane only (they oscillate at 1 angle)
o Light is partially polarised on reflection
- Polaroid
o Long chain molecules that absorb energy from…read more

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Experiment to show two source interference:
- When two loudspeakers are connected to the same signal generator, their signals interact this can
be heard as you walk in front of the loudspeakers.…read more

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In a progressive wave every point oscillates with the same amplitude and every point
oscillates, stationary waves have nodes and antinodes
o In progressive waves all points have a different phase
- Harmonics
o Fundamental mode of vibration ­ lowest frequency stationary wave for a particular
system (first harmonic)
o Harmonics ­ whole number multiples of the fundamental frequency
Experiment to calculate the speed of sound in
air:
- When loud speaker emits a sound wave it is
reflected off the closed end of the…read more

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Only photons with energy > cause electron emission
o (work function) is the minimum energy required to release electrons
o Number of electrons emitted depends upon light intensity, as long as energy is greater than
the work function
o Emission is instantaneous and photons transfer all or none of their energy to electrons
- Experimentally
o Electromagnetic
radiation from lamp
discharges plate and
gold leaf falls
o A single light photon
interacts with a single
electron
o When photon energy
> work function
electron is…read more

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