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Physics experiments
perform an investigation and gather first-hand information to observe the occurrence of different striation patterns for different
pressures in discharge tubes

Aim
o
To observe the effect that different gas pressures have on an electric discharge tube.
 Risk assessment
Risk
High voltages
Flying glass
Explain the precaution
 High voltages may have painful
effects on the body, cause eye
damage if sparks reach the eye, or
can cause burns to the skin.
 The discharge tubes may implode
when scratched or bumped resulting
in flying glass fragments that can
blind you.
Risk minimisation
 Get an teacher to do the
experiment
 Turn off the induction coil when
changing the electrodes.
 Handle the electric discharge
tubes carefully
Equipment:
 Induction coil
 Electric discharge tubes
 Transformer
Method:
1. Set up an induction coil (6V DC). Switch off the power pack.
2. Record the gas pressures of the tube.
3. Input the positive terminal of the induction coil into the common terminal, the anode (+) at the bottom of the discharge
set.
4. Attach the negative terminal of the induction coil to the cathode (-) marked with the highest pressure. Switch on the power
pack.
5. Record the gas pressures of the tube. Observe what happens
6. Repeat each using of the discharge tubes. Describe each pattern.
Results:
 40 mm mercury- purple streamers
 10mm mercury-cathode glows, pink glow in dark space
 3mm mercury-Glows light purple, gap between cathode and
space. Dark purple glow at end.
 1mm mercury-cathode glows, white streamers
 0.1mm mercury- Light green glow at top
 0.02 mercury- grey white glow fluorescent glow.
Discussion:
 As the pressure is reduced, fewer particles collide with the electrons, causing a varying of patterns. Higher pressure = higher
ionisations.

The amount of dark space between the glowing bands increases with further reductions.
Physics experiments
perform an investigation to demonstrate and identify properties of cathode rays using discharge tubes:
 containing a Maltese cross
 containing electric plates
 with a fluorescent display screen
 containing a glass wheel

Aim
o
To determine some of the properties of the rays which come from the cathode of a discharge tube.
Equipment:
 Induction coil
 Maltese cross
 Transformer
 Paddle wheel
 Tubes with fluorescent screens
 Tubes with electric plates
Method:
1. Set up the induction coil (6V DC). Switch off the power pack.
2. Connect DC 6V to the induction coil primary.
3. Connect the induction coil secondary to the electrodes of the discharge tube containing the Maltese cross (Crookes tube)
4. Ensure that the Maltese cross is vertical.
5. Turn on the voltage supply.
6. Adjust the induction coil circuit break to produce a high voltage output and observe the shadow of the cross at the end of
the discharge tube.
7. Repeat the observations with the cross lying horizontally.
8. Replace the Crookes tube with the fluorescent screen display and record the effect of placing a set of bar magnets around
the cathode ray.
9. Use the diode CRT demonstration tube. Observe the electric field on the cathode rays.
10. Use the paddle wheel at and observe the effect that the cathode rays have on the wheel.
Results + discussion:
Investigation + image
Maltese cross
Tubes with electric plates
Explanation/discussion
 The Maltese cross is placed in the path of the cathode rays, causing a clearly defined
shadow at the end of the tube.
 Shows that cathode rays travel in straight lines and are blocked by solid objects.



Tubes with fluorescent screens


This shows that cathode rays are associated with negative charges.
The force produced by the plates electric fields cause the electrons to bend to the
left or right depending on the polarity.
When there is no force from the electric plates, the line is in the middle due to the
fact that the forces of the electric and magnetic field are equal.
A fluorescent screen shows that cathode rays can cause fluorescence. When the
cathode rays collide with the air particles, the reaction produces light.
This demonstrates that cathode rays have energy.
Physics experiments
Paddle wheel

A lightweight glass paddle wheel, able to rotate freely, is placed in the path of the
cathode rays so that the rays strike one edge of the wheel at a tangent. The cathode
rays cause the wheel to spin and move away from the cathode. This demonstrates
that the cathode rays must have momentum, and therefore mass, and that they are
emitted from the cathode.
Conclusion
 It was concluded in the experiment that cathode rays:
o are electrons
o travel in a straight line and do not go through solid objects
o are negatively charged
o collide with air to produce a fluorescent light
o have momentum and mass.
Physics experiments
perform an investigation to demonstrate the production and reception of radio waves

Aim
o
To demonstrate the production and transmission of radio waves
 Risk assessment
Risk
High voltages
Radiation
Explain the precaution
 High voltages may have painful
effects on the body, cause eye
damage if sparks reach the eye, or
can cause burns to the skin.
 The sparks release long wavelength x
rays and short wavelength ultraviolet
radiation.
Risk minimisation
 Get an teacher to do the
experiment


Get an teacher to do the
experiment
Get students to stand 1 metre
and more away.
Equipment:
 Induction coil
 Transformer rectifier with leads
 Any radio
Method:
1. Adjust the gap on the induction coil to 5mm and adjust the transformer to 6V DC
2. Adjust the tuner of the radio , so that it does not receive a station.
3. Move around the room and try to estimate where the radio can receive the static noise from the spark.
4. Adjust the gap to 10mm and repeat the exercise.
5. Change the tuner of the radio and scan across the range of wavelengths.
Results+ discussions:
 The maximum distance from the induction coil where the radio receives static reduces with the increasing gap distance.
 At different wavelengths, there is a higher frequency, pitch. (larger gap).
 The voltage across the gap produces electromagnetic radiation.
 Energy is transferred from the spark to the radio in the form of electromagnetic radiation which oscillate back and forth.
conclusion:
 Radio waves were produced and detected using a spark produced in an induction coil and received with an AM receiver.
Physics experiments
Perform an investigation to model the behaviour of semiconductors, including the creation of a hole or positive charge on the atom
that has lost the electron and the movement of electrons and holes in opposite directions when an electric field is applied across
the semiconductor




We modelled a semiconductor using marbles in a Petri dish, with each marble representing an electron.
Removing a marble from the dish represented the creation of a hole. As the dish is disturbed by moving it, simulating the
application of an electric field, the position of the hole changed as marbles moved in to fill it, moving the hole elsewhere in
the dish.
The gap and the marble moved in opposite directions, as a new gap was created when a marble moved to fill the old gap.
Then we modelled semiconductors using marbles as atoms and a metal ball bearing as an extra free electron that was capable
of moving around the dish as the dish moved. When we moved the dish, the ball bearing moved from marble to marble,
showing the movement of free electrons.
perform an investigation to demonstrate magnetic levitation
Aim: To demonstrate magnetic levitation of a magnet over a superconducting disc
Equipment:
 Liquid nitrogen,
 plastic tweezers,
 High Temperature Superconducting disk (HTS),
 thick cotton gloves,
 neodymium magnet,
 Styrofoam container
Method:
1. A high temperature superconducting disc was placed in a shallow Styrofoam dish and then liquid nitrogen was
carefully poured over the disk until it was covered by about 3 mm of nitrogen.
2. This set up was left for approximately one minute to allow the disc to cool down to below its critical
temperature
3. Using the plastic tweezers, a neodymium magnet was placed carefully above the superconducting disc
4. Observations were recorded
5. Experiment was repeated twice using two different samples of HTS material
Results
 The magnet floated above the superconductor when the liquid
nitrogen had cooled the magnet enough.
 The magnet dropped when the superconductror returned
back to room temperature.
Discussion
 The magnet floats due to the meissner effect. A magnet
placed near the superconductor will induce a magnetic field
inside it (lenz’s law). The superconductor will expel the field as
it has zero resistance, thus making the magnet float.