Page 94 - Physics 10_Float

CURRENT ELECTRICITY

Galvanometer is very sensitive instrument and can detect
small current in a circuit (Fig.14.3). A current of few
milliamperes is sufficient to cause full scale deflection in it.
While making the connections polarity of the terminals of
the galvanometer should be taken into consideration.
Generally, the terminal of the galvanometer with red
colour shows the positive polarity while that of with black
colour shows the negative polarity. An ideal galvanometer
should have very small resistance to pass the maximum
current in the circuit.
After suitable modification galvanometer can be converted Fig.14.3: A galvanometer
into an ammeter (Fig. 14.4). A large current of the range such
as 1 A or 10 A can be measured by means of ammeter. Like
galvanometer, ammeter is also connected in series, so the
current flowing in the circuit also passes through the
ammeter (Fig.14.5).
Battery Knife switch

Ammeter

Fig.14.4: An ammeter
Light bulb
Electric current
Fig.14.5: Schematic diagram showing the measurement of current

14.2 POTENTIAL DIFFERENCE
When one end A of a conductor is connected to the positive
terminal and its other end B is connected to the negative
Do you know?
terminal of the battery, then the potential at A becomes The galvanometer has been
higher than the potential at B (Fig.14.6). named after Luigi Galvano
Direction of current (1737-1798). He, while
dissecting a frog's leg,
V
discovered that dissimilar
A B metals touching the leg caused
it to twitch. This chance
discovery, the invention of the
chemical cell and the battery.
Direction of electrons
K + -
V
Fig.14.6
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