1. Electronic symbols
and ohm’s law

3. An electronic symbol is
a pictogram used to represent
various electrical and electr
onic devices (such as wires,
batteries, resistors,
and transistors) in
a schematic diagram of an
electrical or electronic
circuit. Circuit symbols are

5. A 'blob' should be
drawn where wires are
connected (joined), but it is
sometimes omitted. Wires
connected at 'crossroads'

6. In complex
diagrams it is often
necessary to draw wires
crossing even though they
are not connected.

7. Supplies
electrical energy. A
single cell is often
wrongly called a
battery, but strictly a

8. Supplies
electrical energy. A
battery is more than one
cell.

9. A safety device
which will 'blow' (melt) if
the current flowing
through it exceeds a

10. A transducer
which converts electrical
energy to light. This
symbol is used for a lamp
providing illumination, for
example a car headlamp

11. An on-off switch
allows current to flow
only when it is in the
closed (on) position.

12. A resistor
restricts the flow of
current, for example to
limit the current passing
through an LED. A resistor

13. This type of
variable resistor with 2
contacts (a rheostat) is
usually used to control
current. Examples include:
adjusting lamp brightness,

14. A voltmeter is
used to measure voltage
or potential difference.

15. An ammeter is
used to measure current.

16. A galvanometer
is a very sensitive meter
which is used to measure

17. According to ohm’s law, under
constant physical condition
i.e. constant temperature,
pressure etc. the applied
potential difference is
directly proportional to the
current flowing in the
circuit.
Or, V = RI
Where R is a constant of

18. 

19. hence, according to ohm’s
law, current is
Directly proportional to
potential difference.
Inversely proportional to
resistance.
If the potential difference
is doubled (keeping
resistance the same),
current will also get
doubled. On the other hand,
if resistance is doubled
(keeping potential