The document describes how a gold leaf electroscope works. It has three main parts: the cap, connecting rod, and gold leaf enclosed in a vacuum. When the cap is charged, the similar charges on the cap and leaf repel each other, causing the leaf to rise away from the plate. The leaf can be discharged by touching the cap to earth it. The electroscope can be charged by contact or induction. It indicates the type of charge on the electroscope based on the direction the leaf diverges.

4. It is a device that is used to detect charges. It has 3 main parts, the cap, the
connecting rod and the gold leaf enclosed in a vacuum. When the cap is
charged. The gold leaf will diverge away from the rod
How does a gold leaf electroscope works?
When a charge is put on the disc at the top it spreads down to the leaves.
This means that both the disc and leaves will have the same charge. Similar
charges repel each other and so the leaves rise away from the plate - the
bigger the charge the more the leaves rise

5. The leaf can be made to fall again by touching the disc - you have earthed the
electroscope. An earth terminal prevents the case from becoming live. The
electroscope can be charged in two ways:
(a) by contact - a charged rod is touched on the surface of the disc and some of
the charge is transferred to the electroscope. This is not a very effective method
of charging the electroscope.
(b) by induction - a charged rod is brought up to the disc and then the
electroscope is earthed, the rod is then removed.The two methods give the gold
leaf opposite charges.
The following diagrams show you how the charges spread over the plate and
gold leaf in different conditions.

8. In the last Unit we saw that there are good electrical conductors,
bad electrical conductors and some which lay in between which we
called semiconductors.
Activity I
• Charge a gold leaf electroscope with either a positive or
negative charge using the methods you learned in past Grades,
• What happens to the leaves of the electroscope? What does
this indicate? (
• Now bring a lighted candle near the electroscope plate. What
happens? What does this indicate? (Fig I)

9. • Under normal conditions (at room temperature & atmospheric pressure) the
gas atoms are electrically neutral so the gas does not conduct electricity
(Gases are insulators) as shown by the electroscope remaining charged.
• When heated however, the gas atoms become ionized as a result of their
rapid motion and colliding with each other causing electrons to be displaced
from one atom to another which form positive ions and negative ions and
free electrons that can now move under the influence of an electric field i.e.
can now conduct electricity.(Gases become conductors when they are
ionized )
• The charge carriers in this case are electrons and positive ions and negative .
• The electrical conduction in gases increase when the temperature increases

10. This was studied using a glass tube in which gas could be reduced in pressure(using
the vacuum pump), fitted with two electrodes to which a high voltage could be
applied(The voltage across the tube was changed by changing the variable resistor).
1. At standard pressure (1atm) there was no current (No emitted light from the tube)
2. When the pressure was reduced, and a voltage of about 5 x 104 volts applied a
light was seen inside the tube. This is due the ionization of gas under low
pressure and high voltage (5 x 104 volts ). which will make the gas a conductor
Fig 2

11. 3. When the pressure was reduced further. (See Fig 2)
In the year 1808 a German scientist (Plucker ) discovered that
when the pressure was reduced to 1.3 x 10-4 atm (or 1.3 x 10-4 bar or 0.1
mm Hg) the light will disappear and a new phenomena was observed that
is the cathode sent invisible rays through the tube which were only
detected when they struck the anode or the glass of the tube causing a
bluish glow. These were called cathode rays and the name has stuck,
though now we know them to be a stream of electrons.
Fig 2

12. When the potential difference is increased more. The high voltage between
the electrodes accelerates the electrons so, the kinetic energy of the
electrons will increase to a specific value as a result of the high electric
field that produced of the high voltage difference inside the tube. Then one
of the following cases might occur.
1. The electrons will collide with the gas atoms and excite them to a higher
energy state. The excited atom returns back to ground state which will
release the energy as light.

13. 2. If the kinetic energy of the electrons increased more the electrons will ionize the
gas atoms, electrons may collide with the atom with high energy that it will cause
another electrons to be emitted from the atom. They too will strike other atoms
and further electrons/ions will be formed so the gas ionization will continue and
the overall result is that the gas conducts electricity.

14. What causes the emission of light in the electric discharge tube?
When an electron collides with an atom, the atom will either be excited or
ionized. This can create two possibilities to the emitted light
1) When the excited atom returns back to ground state which will release the
energy as light.
2) 2) During the recombination process when a positive ion meets an
electron, energy will be released as light
What causes the bluish glow near the anode in the electric
discharge tube?
When the cathode rays (electrons) hit the anode or hit the glass and
loss their energy, , the tube releases a bluish glow

15. How does electric conduction occur in solids,
electrolytes ,gases, and semiconductors?
• Solids conduct electricity by the motion of free electrons
(Electric conduction).
• electrolytes conduct electricity by the motion of positive &
negative ions (Ionic conduction).
• Gases conduct electricity by the motion of positive ions and
negative ions and free electrons.
• semiconductors conduct electricity by the motion of
electrons and holes.

16. In order to gases conduct electricity, two conditions are required. First, the normally
neutral gas must create charges or accept them from external sources, or both. Second,
an electric field should exist to produce the directional motion of the charges.
Note