Advanced notice article Flashcards
Explain the term inertia, and state the property of an electron that results in the beam having low inertia.
Inertia is resistance to change in motion, quantifiable as inertial mass.
Property of electron – its mass.
Explain how a time-varying signal can be displayed repeatedly on the oscilloscope.
Periodic voltage applied to X plates: sweeps beam across screen and back.
Signal to be measured applied to Y plates: deflects beam vertically by an amount proportional to the voltage. [1]
what does 1 HZ rpresent
1 sample per second
How many times is the signal sampled during the 5 ms of recording a trace, if the sampling frequency is 20 000 Hz? [1]
20000 x 5x10^-3 =100samples
how to find the amount a signal is sampled
length of recording trace x sampling frequency
How much information (in bits) is recorded for a single trace? [1]
number of bits x number of samples
Data rate =
data per trace x number of traces recorded per second
bits per trace x traces per second
Quantisation error =
1/2^nbits, can times by 100 to get percentage
capacity=
mass x density
The actual force produced by the engine will be considerably larger than that calculated
Forces calculated are resultant forces [1]
Actual force provided by engine must be larger due to friction/air resistance [1]
Resultant force =
Engine force – Resistive forces
inertia
quantifiable as inertial mass
resistance to change in motion
why has a beam of electrons got low inertia
because it has low mass
why sampling frequency must be double
to capture adjacent peaks and troughs of signal
to find the height of a trace
ndivisions x size of one division /new size of division
Hertz meaning
samples per second
information per trace=
number of samples x bits
Data rate=
data per trace x number of bits
bandwidth units
Hertz
if too many bits are used
noise is digitised
worst case quantasitation
1/2^n bits
as a percentage
mass=
capacity/density
a big pendulum angle
affects the time period
a small pendulum angle
difficult to keep constant
how to minimise uncertainties
pendulum
plot graph to get gradient
repeat each measurement
10 full oscillations
measuring blob with micrometre
benefits of a graph
remooves systematic error
scatter of points indicate overall effect of uncertainties
finding uncertainties in graph
uncertainty bars, maximum minimum gradient
these gradients can be used to calculate a percentage uncertainty
coherent
the same
