Chemical EFFECTS of Electric CURRENTS Part 1 – Physics Class 8th CBSE #11

Chemical EFFECTS of Electric CURRENTS Part 1 – Physics Class 8th CBSE #11


In your previous grade you must have learnt
about electrical conductivity in solids. There are good conductors of electricity,
weak conductors of electricity and bad or non-conductors of electricity. Here we’ll see how they behave. In this set up, all the connections are there,
only one part is missing and that will tell us about the electrical conductivity of the
3 materials. Good conductors, like copper, are the materials
that easily let electricity flow through them. Lets try it. The bulb is nice and bright. Weak conductors allow electricity to pass,
but a lot of it is lost during this transfer. The lead from a pencil is a good example of
a weak conductor and you can see that the bulb is not as bright. Bad or non-Conductors don’t allow any electricity
to pass, like rubber or plastic. Here the bulb does not glow at all. Thats why its good to wear rubber slippers
or shoes when touching any electrical item. In this lesson we will see that even liquids
can be of all 3 types, as they were in solids. they can be good, weak or poor conductors
of electricity. Liquids that are good conductors of electricity
are solutions of Acids, bases and salts in water. Solutions of Acids can be prepared by adding
sulphuric acid, hydrochloric acid or any other acid in water. Vinegar and lemon juice is can also be used
as vinegar has acetic acid and lemon juice has citric acid. Solutions of bases can be prepared by adding
sodium hydroxide potassium hydroxide or any other base in water. Solutions of salts can be prepared by adding
copper sulphate or sodium chloride, which is common salt, or any other salt in water. Lets also prepare ourselves with liquids that
are poor or weak conductors of electricity, for that we need distilled water or a sugar
solution. Before we do the experiments to actually see
the conductivity, you should know a few more things related to electrical conductivity
in liquids. Firstly, Liquids conduct electricity through
themselves in a way that’s different from solids. First difference is: In solids, electricity
is carried by the electrons through the solid, but in liquids it is carried by the positively
charged and negatively charged ions. For example in the copper sulphate solution,
electricity is carried by the copper ions (Cu2+) and Sulphate ions (SO42-). Second difference is: in solids there is no
chemical change taking place when electricity is passed through it. In liquids, there is a chemical change taking
place when electricity passes through it. For example when electricity passes through
water, H2O, a chemical change takes place where the water decomposes into hydrogen and
oxygen gases. Secondly: Liquids or solutions that conduct
electricity are called electrolytes. Therefore its obvious that a strong electrolyte
means that it’s a good conductor of electricity, and thats because it has more ions. These are all strong electrolytes Sulphuric
acid solution, Nitric acid solution, Sodium Hydroxide solution, Potassium Hydroxide solution,
Common Salt solution, Copper sulphate solution, Silver nitrate solution, etc. Once again its obvious that a weak electrolyte
means that it conducts electricity, but to a lesser extent,it’s weaker and thats because
it has a lesser number of ions. These are called weak electrolytes. Vinegar or acetic acid solution, Lemon juice
which is citric acid solution, Ammonium chloride solution, tap water, rain water, etc. Thirdly: To conduct electricity through liquids,
there needs to be 2 sets of solid electrical conductors that are in contact, or dipped
in the liquid. These are called an electrodes. Since any DC current has a positive and negative
terminal, like all batteries have, the electrode connected to the positive side is called the
anode, and the electrode connected to the negative side is the cathode. “A” of anode comes before “C” of cathode,
plus comes before minus, this is how i used to remember it. Lastly: If we have this electrolyte in a container,
and have these electrodes in place, this whole arrangement is called an electrolytic cell
(show). Keep in mind one thing, these electrolytes
are not as good conductors of electricity as solids. This means we’ll need more than one electric
cell, in fact we need a battery of cells, to pass electric current through the electrolyte
to study the chemical effects of electric current. Instead of the battery we can also use whats
called an eliminator that can convert alternate current to direct current at the required
voltage. Now we know all the parts and factors that
we need to consider when we study electrical conductivity in liquids. So heres a nice looking set-up. And i’ll show you how to make it in the
TIY of the lesson. You can see that this circuit is complete
and the light is coming on. Now when i turn this, the two electrodes are
not touching each other anymore and you can see that the light has gone off, and it means
now that the circuit is broken only from this part, and now what we’ll do is we’ll dip
these electrodes into various solutions to see which ones conduct electricity and how
much. And are they strong, weak or poor conductors
of electricity. In some situations, it might be that the bulb
doesn’t glow because there is not enough current flowing through the circuit to heat the filament
of the bulb enough to make it glow, but then there might still be a weak current passing
through. To detect the weak current, we can use a very
low power LED, you can see that the LED glows even with the low current passing through
the circuit. In fact the LED looks quite bright actually. Now I’m putting some copper sulphate into
distilled water and lets see the bulb now. With just 6volts battery the solution didn’t
manage to get the torch bulb to light up, but the LED lights up once again. Now let’s try the vineger. Once again, the LED lights up quite well. Now let’s put drinking water, the LED is
also just about lighting up, its not as bright as it was before. This time I have squeezed 3 limes and have
put equal amount of water, let’s see how well this solution conducts electricity. Hey, the LED is bright again. Now i’ve put some sugar into distilled water
and dissolved most of it, and the LED is glowing mildly. Not too bright though. Now’s the turn of distilled water which
is supposed to be a poor conductor, and yes, even the LED doesn’t glow And if this LED also doesn’t glow, then we
can a magnetic compass with a decent amount of wire of this circuit wrapped around the
compass. If there is a current passing through the
wire, it will create a magnetic field, and that will disturb the magnetic field of the
compass and the needle will get deflected. In these weak conductors of electricity, there
is a small deflection that we can see. We can also change the conductivity of a liquid. The distilled water was not conducting electricity
but then if we add some salt to it and start stirring it, lets see what happens. Now there is a weak current passing through
it. We can do the same thing by even adding acids
to the solution or base to the solution to increase the electrical conductivity in a
non conducting liquid. We can even increase the amount of electricity
passing through the circuit by increasing the amount of current passing through it. Regular tap water manages to conduct electricity
because of mineral salts dissolved in it. This is why its dangerous to touch electric
points with wet hands. In fact even rain water conducts electricity
because when it falls through the air, it reacts with the many gases on the way, mainly
carbon dioxide to form a weak carbonic acid. During the rainy seasons, some animals and
humans die because of getting electrocuted when they touch electric poles even if they’re
made of cement. And this happens because the pole is wet with
the rain and the wetness can connect the live wire at the top to the point where they’re
touching it. This is also the same reason why the firemen
first switch off the electricity of a building on fire, before they start throwing water
on it. Let me show you an example of this as an experiment. Here the water is flowing out. One electrode is inside the container, and
the other is on the flowing stream outside. Will it conduct? Well, it does! It conducts even here when i touch one electrode
to the stream and other to the place its falling into. This means that if the fireman uses a hose,
the electricity could travel all the way up to him through the steam of water itself. Now lets do a recap and move on to the TIY
project. Similar to solids, liquids can also conduct
electricity Liquids can be good, weak or poor of electricity. Liquids that are good conductors of electric
are solutions of acids, bases and salts. Weak conductors of electric are liquids like
Vinegar, lemon juice etc Poor conductors or non conductors of electric
are liquids are like sugar solution and distilled water. Liquids conduct electricity differently from
solids. First difference is: In liquids the electricity
is carried by the positively charged and negatively charged ions.
and the second difference is: In liquids, there is a chemical change taking place when
electricity passes through it. Liquids or solutions that conduct electricity
are called electrolytes. Strong electrolyte means that it’s a good
conductor of electricity. A weak electrolyte means that it’s a weak
conductor of electricity. To conduct electricity through liquids, there
needs to be 2 sets of solid electrical conductors, called electrodes, dipped in the liquid. The electrode connected to the positive side
is called the anode. The electrode connected to the negative side
is the cathode. This whole arrangement with the electrolyte
and the electrodes is called an electrolytic cell. The current flowing through the electrolytic
cell can be best detected by using a filament based torch bulb. A weaker current can be detected by a very
low power LED bulb. The weakest of the currents can be detected
by the disturbance of the magnetic field of a compass. Tap water can conduct electricity because
it has natural minerals dissolved in it. Rain water conducts electricity because of
reactions with gases when it falls though the air. It is dangerous to touch any electrical point
if your hands are wet, or even if the place is wet. Firemen first switch off the electricity of
a building on fire, before they start throwing water on it. Now let us see how to make the nice looking
set up that i used in the lesson. And we’ll also try and understand other
factors that can improve or cause problems to the experiments that you can do with this
set up. You’ll need these PVC pipes and joints. All the lengths are given on screen. All the pipes are of 20mm diameter (thats
about 3/4 of an inch). Now while you can see how I’m putting things
together, let me tell you that some of these kinds of pipes are sold under the name of
pipes and some are called tubes, like when you buy pipes for furniture, you are buying
tubes. The difference is, when we talk about a pipe
then if i say the diameter is 20mm, it means the “inner diameter” is 20mm. The thickness of the pipe will add to it. This is because when it comes to pipes, material
has to flow through it, so the inside space is important. But when it comes to tubes, like in furniture,
nothing is flowing inside, so a diameter of 20mm will mean that the outer diameter is
20mm. So thats the difference in buying pipes or
tubes. So now that our structure looks like a cute
animal, you can glue a pack of 4 AA batteries as shown. 4 AA at 1.5 volts each means a total of 6
volts. We tried with 2 batteries and even a 9 volt
battery, but found the 6 volts giving the best results. Be very careful using hot glue. In the earlier lesson i showed how to use
a glue stick even if you don’t have a glue gun. You could even tape the battery pack too instead
of using glue. Now we need to glue the filament based torch
bulb holder on the smallest piece of pvc pipe as shown. We could have directly glued it on the “animal”
but then changing it would be difficult and later you’ll see that we have to change
it. The positive terminal of the battery is connected
to the positive terminal of the bulb holder. On the other side is connected to a crocodile
clip, which is glued to the pvc pipe as shown. The negative of the battery is connected to
another clip and glued to the same pvc pipe at a little distance. The distance could be 2.5 to 3 cm between
the clips. Make sure you glue only one half of the crocodile
clips otherwise if you glue both sides, then it wont open its mouth. But make sure your finger doesn’t touch the
glue. You could hold it with something else so that
your fingers are safe. Put some glue on the back of the structure
also, to hold the wires so that they don’t keep floating around. Now you can clip two long iron nails to each
of these clips and you are ready to start experimenting. To check if the rest of the connection is
fine, connect the nails to each other by another metal piece, there, it’s all working. And if it doesn’t work then check the batteries
and if the batteries are fine then all the connections, and importantly the bulb as well. Because these bulbs keep getting fused. In some liquids that are poor conductors of
electricity, the bulb doesn’t come on, but you can see the bubbles in the solution, it
means the current IS flowing. For those experiments, you can use LEDs to
see if the current is passing, because these bulbs take a lot less current than these filament
based torch bulbs. But then we use these bulbs because they show
a much better range of glowing light. LEDs have a positive and negative connection
too. The longer arm of the LED needs to be connected
to the positive of the battery. Also don’t connect the LED directly to the
battery because if its a less voltage LED, the 6 volt pack might burn it. When the current is really small, and even
the LED doesn’t come on, then you can also show the current by creating a deflection
in the magnetic field of a compass. This can b done by winding a coated copper
wire on a compass, around 30-40 times as shown. Remember to remove the coating from the ends
of the wire where you will clip it to the circuit and then attach this instead of the
bulb to the circuit. Now i’m sure you can see why we didn’t glue
the bulb holder directly on the stand. Also note that the deflection will happen
only once when the circuit gets completed. So you will have to disconnect it and then
connect it once again to show the deflection if you want to do it again. You can also connect the circuit to a battery
eliminator if you have one, because then you don’t have to waste money on batteries that
you have to keep throwing away once they’re finished. Now you’re armed with all the material and
information to test out electrical conductivity in different liquids. Always do these experiments in well ventilated
rooms and DO NOT USE ACIDS. Just use safe liquids like juices, vinegar,
tap water, distilled water, oils, etc. Things required for the TIY project:
PVC plumbing items, the dimensions were given earlier. 4 Pencil batteries and connectors. Filament bulb with holder. Four crocodile clips. Iron Nails. Metal strip. LED light bulb. Glue gun, you can do without the glue gun. A mallet. Bowl for different solution. Different liquid solutions as mentioned. Magnetic compass. Double sided tape. Copper wire. Sandpaper. Thats all for now, in the next lesson we will
start experimenting with chemical effects of electric currents. It’s going to be electrifying, but it’s
safe. Join me there.

1 comment / Add your comment below

  1. Dear sir explanation and diy project is very good one. I solute for your efforts. Your video is very useful for secondary students. 👌👌👌.👍👍👍 I think that it will be better to leave the wires inside the tubes to make your project more smart.

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