G482 Flashcards
Describe what is meant by the term mean drift velocity of electrons in a wire
The average displacement/distance travelled of electrons ALONG THE WIRE per second
On average they move slowly in one direction through metal/Cu lattice when pd across wire
because they collide constantly
Define the resistivity of a metal wire
p=RA/l
resistivity= resistance x area / length
Describe the significant features of the graph in terms of current, voltage and resistance
(Threshold v=1.5V)
No current until V is greater than 1.5V
brightness/intensity of LED increases with current/ voltage above 1.5V
LED doesn’t obey Ohm’s law
as I not proportional to V
Below 1.5V, LED acts as an infinite R(very high)
Above 1.5V, LED resistance decreases (with increasing I/V
When designing a circuit which includes an LED, it is normal practice to connect a resistor in series with the LED. Suggest and explain the purpose of this resistor
The resistor limits the CURRENT in the circuit, otherwise it could overheat/burn out
Define frequency
The number of waves passing a point per unit time
Define speed of a progressive wave
Distances TRAVELLED BY THE WAVE per unit time
Explain what us meant by infra-red radiation
Part of the em spectrum
Lower f or longer wavelength than visible light
State the equation linking wavelength, speed of light and frequency
Wavelength=speed of light/ frequency
Use the ideas of path difference or phase difference to explain how the interference pattern is formed
Path difference n(lambda) for constructive interference
Produce maximum amplitude/intensity
Path difference (2n+1)(lambda)/2 for destructive interference
Produce minimum amplitude/intensity
State the effect on the POSITION and INTENSITY of the maxima when the amplitude of the transmitted waves is doubled
Intensity increases by factor 4
Position unchanged
State the effect on the POSITION and INTENSITY of the maxima when the separation between the transmitters is halved
Intensity unchanged
Distance apart of maxima doubled
State the effect on the POSITION and INTENSITY of the maxima when the phase of transmitter A is reversed so there is now a phase difference of 180 degrees between the waves from A and B
Intensity unchanged
Maxima move to positions of minima and vice versa
Write a suitable word equation to define the resistivity of a material
Resistivity=resistance x cross-sectional area/length
Give one example where LEDs are commonly used. Suggest one advantage of using LEDs in place of filament lamps
Torch bulb, traffic light, car rear lamp
Draws a lower current, more efficient at converting electrical energy into light, if one LED fails others are still lit, greater lifetime
What is terminal potential difference?
energy AVAILABLE TO BE transferred from electrical to other forms PER UNIT CHARGE
Or
Energy transferred ACROSS THE TERMINALS from the supply PER UNIT CHARGE
