Transcript oscilloscopes - physicscoffeeshop

Reading from an Oscilloscope
The Oscilloscope
•An oscilloscope is a piece
of scientific equipment
which is used to measure
voltage which is changing.
They are very useful for
studying waveforms.
•The screen looks similar
to a piece of graph paper.
•The controls set the scale
of the display.
How does it work?
1. Electrodes which deflect the
electron beam. (make the dot
move on the screen)
2. Electron gun – fires electrons
towards the screen.
3. Beam of electrons (tries to
spread out as electrons repel
each other)
4. Coil produces a magnetic field
which focuses the beam.
5. Phosphor atoms on the inside
of the screen glow green
when electrons hit them.
Reading from the oscilloscope
•Y-axis displays amplitude
of a voltage.
•X-axis displays units of
time
•AC – a current that is continuously changing
between positive (+) and negative (-) voltage.
Mains AC has the shape of a sine wave, because of
the way it is generated.
Wavelength and Amplitude
•Period (distance between two
equivalent points on wave)
0V
•Voltage peak-peak
•Amplitude
of wave
Frequency
•Frequency of a wave is the number of waves passing
a fixed point per second.
•Measured in Hz – number per second.
frequency = number of waves / time for waves to pass
•One Hz
•Two Hz
•X-axis 0.005s
per division. ?Hz
Frequency
frequency = number of waves / time for waves to pass
= period / time
•X-axis 0.005s
per division.
•One wave passes in 4 x 0.005s = 0.02s
•Frequency = 1 wave / 0.02s = 50Hz
Mains in the UK
•UK mains supply is 230V amplitude, 50Hz.
•The ‘live’ voltage supply is the one which is
continuously changing between +230V and -230V
at 50Hz. *This varies above and below neutral which
is at approximately 0V but can be different as
neutral is earthed at the sub-station which can be
some distance away.
*HT only