Page 100 - Chemistry ICSE Class IX

88 ICSE Chemistry – 9
ƒ Charge on an electron (e). An electron possesses one unit negative
charge. It has been found to be the smallest negative charge that any
particle can carry.
Charge on an electron, e = –1.602 × 10 –19 C
C is the symbol of coulomb unit.

EXAMPLE 4.1. A student weighs 30 kg. Suppose his entire body is made up of
electrons. How many electrons are there in his body? Compare the total number
of electrons in his body with the population of India (say 1 billion).
Solution: Mass of the student = 30 kg
Mass of electron = 9.1 × 10 –31 kg
If it is assumed that the body of the student is made up of only electrons, then

30 kg
No. of electrons in student’s body = = 3.3 × 10 31
9.1 × 10 –31 kg
31
Thus, the body of the student will consist of 3.3 × 10 electrons.
Population of India = 1 billion = 1 × 10 9
Total no. of electrons in the body 3.3 × 10 31
So, = = 3.3 × 10 22
Population of India 1 × 10 9
Positive Rays (Anode Rays or Canal Rays)

During his working with cathode rays, Sir J. J. Thomson had noticed a red
glow around the cathode, but on the side opposite to the anode. To know
the reason for this glow, he designed a discharge tube with a perforated
cathode xed in the middle of the tube, as shown in Fig. 4.6.

:͘ :͘ dŚŽŵƐŽŶ ůĂƚĞƌ ƐŚŽǁĞĚ ƚŚĂƚ ƚŚĞƐĞ
ƌĂLJƐ ĐŽŶƐŝƐƚĞĚ ŽĨ ƉŽƐŝƟǀĞůLJ ĐŚĂƌŐĞĚ
ƉĂƌƟĐůĞƐ ĂŶĚ ǁĞƌĞ ƚŚƵƐ͕ ŶĂŵĞĚ ĂƐ
posiƟve Žƌ anode rays͘ dŚĞƐĞ ƌĂLJƐ
ǁĞƌĞ ĂůƐŽ ĐĂůůĞĚ canal rays.

Fig. 4.6 The discharge tube used in the production/detection of the anode rays
On applying electrical potential across the two electrodes, a green
uorescence was seen in the glass tube at one end while on the other end,
a red uorescence was seen. The green uorescence was due to cathode
rays. Obviously, the red uorescence was due to some other type of
emission.

How are positive rays produced
Cathode rays consist of negatively charged particles called electrons. These
electrons move away from the cathode with very high speeds. These fast-
moving electrons split the molecule into atoms and remove one or more
electrons from the atoms. Thus, the atoms get converted into the positive
ions due to the loss of electrons. These positive ions pass through the holes
in the cathode plate to produce a glow on the glass wall of the discharge
tube.
A stream of these positively charged particles is called a positive ray
(or anode ray).