electricty

1. CURRENT ELEC

2. CURRENT ELECTRICITY
SS1PHY
LESSON CONTENTS
 PRODUCTION OF
CONTINUOUS CHARGES
 ELECTRIC CELL
 PRIMARY CELLS
 SECONDARY CELLS

3. PRODUCTION OF CONTINUOUS CHARGES
SS3PHY
A continuous flow of charges is produced from
primary & secondary cells.
ELECTRIC CELL: An electric cell is a device used to
generate the required force to move the electron
through the internal & external circuit. There are two
types of electric cell. They are the PRIMARY &
SECONDARY CELLS.
PRIMARY CELL: The primary cells are cells that
produce current as a result of non-reversible chemical
changes taking place b/w the various components of
the cell. They give out electrical energy directly from
their store energy for some time. The primary cells
have high internal resistance E.g. Simple cell, Daniel

4. SIMPLE CELL ( VOLTAIC CELL)
SS3PHY
A simple cell consists of a glass vessel containing
dilute H2SO4 acid, two electrodes of Zn(-) & Cu(+) that
are immersed in the dilute acid. The bulb light up when
the Zn (cathode) & Cu (anode) plates are connected to it
throw wire showing current is flowing through it.
Defects of the
simple cell
 Polarization:
Formation of H2
bubbles around the
Cu plate
 Local action: Due
to impurities on the
Zn plate

5. THE DANIEL CELL
SS3PHY
It consists of a Cu vessel filled with a saturated
CuSO4 soln., a porous pot containing H2SO4 acid & an
amalgamated Zn rod immersed in the acid. Dilute H2SO4
is the electrolyte, Zn (-), Cu (+) & CuSO4 acts as the
depolarizer for the cell

6. THE LECLANCHE CELL
SS1PHY
In 1866 George Laclanche invented a dry cell
which was named after him. The Leclanche cell are of two
types namely Dry & Wet Leclanche cells.
The wet Leclanche cell: Consists of a carbon rod (+) in a
porous pot with mixture of Manganese dioxide & powered
carbon parked around the carbon rod, a glass jar filled
with a soln of NH4Cl & a Zn (-) rod immersed in the
NH4Cl soln. NH4Cl is the elect
rolyte & the Manganese dioxide
is the Depolarizer.
Disadvantages
 Too cumbersome to carry about
 Rate of depolarizer slower
than rate of H2 liberation

7. THE LECLANCHE CELL
SS1PHY
The Dry Leclanche Cell: This is the
common radio/torch battery. It consists of a
carbon rod (+) in a muslin bag containing a
mixture of manganese dioxide (depolarizer) &
powdered carbon around the carbon rod; a Zn (-)
container that contains a paste NH4Cl
(electrolyte) surrounding the muslin bag.
Cardboard disc at the bottom prevent the carbon
rod from touching the Zn(-) container. Pitch seal
& a brass cap over the carbon rod at the top. It
has the same disadvantages just like the wet

8. THE LECLANCHE CELL
SS3PHY

9. SECONDARY CELLS ( ACCUMULATORS)
They are cells from which current are
produced due to reversible chemical change
within the cell. They can be charged or restored
with current. They have very low internal
resistance & so can provide large currents for a
long time.. The change in p.d is very small.
Uses: (a) To start engines in vehicle
(b) Provide sparks for ignition
(c) Provide current in telephone cable.
Types of Secondary Cells
(1) Lead-Acid Accumulator

10. It consists of a positive pole of PbO5 (+) , Pb (-)
pole & dilute H2SO4 (electrolyte).
ALKALINE or NICKEL-IRON (NiFe)
Consists of Ni(+) plate, Fe (-) plate
& KOH as electrolyte.
LEAD-ACID ACCUMULATOR
SS1PHY

11. Using or discharging an Accumulator
SS1PHY
When in use or discharging, it supply current to
external loads. Current flows from the (+) to (-) terminal
conventionally as the key is closed.
The load goes dim &
off after sometime with
ammeter indicate no reading
when discharging.
When fully disharged, the relative
density of the acid fall to 1.15

12. Charging or Recharging an Accumulator
SS3PHY
Direct current (d.c.) is passed through it in
opposite direction to which it supplies current. When the
key is closed, current flows through the (+) terminal & out
through the (-) terminal. A variable resistor is used to
regulate the flow of current. It has an e.m.f. of 2.2V& a
relative density of 1.25 when fully charged.

13. Differences b/w Primary and secondary cells
SS1PHY
S/N Primary Cell Secondary Cell
1 Low initial cost Higher initial cost
2 Disposable after
use
Regular maintenance
required
3 Not all are
periodically
recharge
Periodically recharge
4 Suitable of portable
applications
Not suitable for portable
applications

14. SS3PHY
1. Draw a primary cell & explain the
common defects of a primary cell.
2. State two advantages of a secondary cell
over a primary cell.
3. Draw a labeled diagram to show the
essential parts of a dry Leclanche cell.
4. With a diagram, chemical symbols and
equations, explain processes of charging
and discharging of an accumulator.
SUBJECT: PHYSICS
TOPIC: ELECTRIC FILED II
ASSIGNMENT N0. 4

15. THANK YOU