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G482 ­ Electrons, Waves and Photons; Revision Notes
Module 1: Electric Current

Electric Current
· A net flow of charged particles.
· Electrons in a metal
· Ions in an electrolyte
Conventional Current
· A model used to describe the movement of charge in a circuit. Positive to negative

Page 2

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G482 ­ Electrons, Waves and Photons; Revision Notes
Module 2: Resistance

Potential Difference
· Electrical energy transferred per unit charge, when electrical energy is converted into another form
· Electrical energy to light energy in a light bulb
Electromotive Force
· The energy transferred per unit charge when a type…

Page 3

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Experiments to Determine I-V Characteristics
· Set up a circuit diagram as shown:


Long Thin Wire
· As to keep the current low, so that heating effect is negligible, always use a long thin wire

· Take readings from the voltmeter and ammeter

· Increase the number of…

Page 4

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Negative Temperature Coefficient (NTC) Thermistors
· These show a rapid change in resistance over a narrow temperature change
· Resistance decreases as the temperature of a NTC thermistor increases
· The rate at which energy is transferred
Fuses as Safety Devices
· These are devices introduced into circuits to…

Page 5

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G482 ­ Electrons, Waves and Photons; Revision Notes
Module 3: DC Circuits

Voltage and Current in Series
· Voltage is shared and current is constant
Voltage and Current in Parallel
· Current is shared and voltage is constant
Kirchhoff's Second Law
· The sum of the e.m.f round a loop…

Page 6

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Progressive Longitudinal Waves
· The motion of particles are parallel to the direction of propagation
Progressive Transverse Waves
· The motion of particles is perpendicular to the direction of propagation
Displacement of a Wave (x)
· The distance from a given point on the wave to its equilibrium/rest point

Page 7

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Wave Speed
· The speed at which a wave travels

· When talking about waves, this becomes

· But since ; it becomes
How a Progressive Wave Transfers Energy
· In the case of light, energy is transferred from a source to your eye
· The wave front…

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· All electromagnetic waves travel at the speed of light (3x108ms-1)

· All posses a magnetic wave and an electrical wave interlocked at right angles to each other

· All are transverse waves

· All can travel through a vacuum

· UV-A: Wavelength 315-400nm
o Causes tanning when skin is…

Page 9

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· The formation of points of cancellation and reinforcement, where 2 coherent waves pass through each
· Two waves with a constant phase relationship
Path Difference
· The proportion of a wavelength by which two waves are `out of synch'
Constructive interference
· When 2 waves reinforce…

Page 10

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2nd order (n=2)

Light of 1st order (n=1)
wavelength 0th order

Grating with slits d 1st order (n=1)
2nd order (n=2)

3rd order (n=3)

· The equation involving , then becomes

· If the grating has X slits per metre, the slit spacing,

G482 ­ Electrons, Waves and…


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