Polarity Test and Identification of AC and DC
According to the
nature of flow of current and magnitude of voltage with respect to time voltage
and current are of two types. In this article I will describe various methods
available to identify ac and dc and there polarity too.
Polarity Test of DC Using Voltmeter Method:
The polarity of
dc can be test using a very simple method known as voltmeter method. In this
method we have to simply connect the voltmeter to the dc supply. Connect the
positive or red wire of the voltmeter to any one terminal of the supply and
connect the negative or black wire to the other terminal of the supply voltage.
Remember that for this process we have to use moving iron type instrument. If
the needle or pointer deflects in clockwise direction this indicates that the
terminal connected to the positive of voltmeter is positive of dc supply and
the terminal connected to the negative of voltmeter is negative of supply. If
the voltmeter deflects in reverse direction this indicates that the supply
terminal are just opposite of voltmeter terminal.
The same test can
be done using a digital multimeter. All the process will be same as in case of
analog voltmeter, only you have to rotate the selector switch to the high value
of dc range if you don’t know the rating of supply or if you know the rating
than place the selector switch just higher than the rating of supply. If the
digital multimeter shows positive reading this means that positive wire of
multimeter is connected to the positive of supply terminal and the negative
wire of multimeter is connected to the negative of supply terminal. If the
reading is negative this means this the digital multimeter terminal are just
opposite of supply. In simple positive of supply is connected to negative of
multimeter and negative of the supply is connected to the positive of the
multimeter.
Polarity Test of DC Using Potato Method:
Take a piece of
potato and cut the potato into two equal pieces. Insert the two supply wire
leads in the potato about 1 cm to 2 cm deep as shown in the picture. Remember
that the distance between the two wires not too close as this will cause direct
short circuit. Switch on the power supply. As soon as you switch on the power
supply you will see greenish color circle around one of the wire. The wire
which is surrounded by greenish color is the positive one and the rest one is
negative.
Polarity Test of DC Using Salt Water Method:
Take a glass of
water and add few drop of salt in it and stir the salt in water. Remember the vessel used for this test should
not be metal, glass vessel is best for this test. Solder each supply terminal
with a piece of iron rod and insert the two supply terminal inside the salt
water solution. To avoid short circuit you can use an insulator like rubber or
glass in between the two iron rod. Switch on the power supply. As soon as you
switch on the power supply you will see gas bubbles are produced from one of
the rod, this is the positive wire and the rest one is negative. If you add sulfuric
acid in the water instead of salt gas bubbles will produce from the negative
wire.
Polarity Test of AC Using Neon Lamp Method:
This is a very simple
test just simply touch one of supply wire using a neon lame tester. If the neon
lamp glows this means that the touched wire is phase and the rest one is
neutral. If the neon lamp does not glow just switch the neon tester to the next
one. Sometime neon tester glows in both the wire this does not means that both
the wire is phase. I will explain it in my next article briefly. Remember that
neon tester operate at 60 volt onward. So if you will test the polarity using a
neon lamp make sure that the supply voltage is greater than 60 volt. To test ac
below this voltage we have two different methods.
Identification of AC or DC Using Potato Method:
This test is very
similar to polarity test of dc using potato method. The only difference in this
test is in the result. In simple you will observe greenish color circle in the
wires unlike dc. A beautiful sketch is shown below for better understanding.
Identification of AC or DC Using Salt Water Method:
This test is
similar to polarity test of dc using salt water method. Arrange all the things
as described above and switch on the power supply. In this test you will
observe gas bubbles are produced from both the wire. The same observation is
for both salt water solution and for sulfuric acid and water solution.
