Q A current of 0.5 A is drawn by a filament of an electric bulb for 10 minutes. Find the amount electric charge that flows through the circuit.
Sol: Given, I = 0.5 A, t = 10 min =10×60 = 600 s
I = Qt
, Q = I × t =0.5 × 600 = 300 C
Q A lightning strike transfers 10 C of charge to the ground in 2 ms. Calculate the current during the lightning strike.
Sol:- Given, Q = 10 C , t = 2 ms = 2 ×60 = 120 s, I = ?
I = Qt = 10120
= 0.083 A
Q Calculate the charge when current of 36 ampere is flowing through a wire in 12 second.
Sol:- I =36 ampere , t = 12 s, Q = ?
I = Qt , Q = I × t = 36 × 12 = 432 coulomb
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Direction of Current The flow of current is assumed to be from positive to negative direction. The flow of electrons is from negative to positive.
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Classification of Solid Substances:- on the basis of current flow
Good Conductor(Conductor):-Substances which allow electric current to pass through them are called conductor. NOTE:-Conductors have free electrons due to which they conduct electricity.
EX:-Metals: copper, aluminium, silver, iron etc
Non-metals: Graphite Bad Conductor (Insulator):- Substances which do not allow electric current to pass through them are called insulators. They have no free electrons. Most of the non-metals are insulators, e.g. asbestos, rubber, wood, glass, plastics, sugar, pure water etc.
Conductivity in liquid:
Liquids which are good conductors: Some liquids too can conduct electricity, e.g. tap water, lemon juice, vinegar, salt solution, etc. Most of the liquids which conduct electricity are solutions of acid, base or salt.
Liquids which are bad conductors: Some liquids are bad conductors of electricity, e.g. distilled water, honey, milk, vegetable oil, etc.
Tap water conducts electricity because it contains various salts dissolved in it. Hence, it is advised not to touch an electric switch with wet hands.
NOTE:-
In Solid, flow of electric current is due to movement of electrons while
In liquid, flow of electric current is due to movement of negative and positive ions.
Q How one can test that given substance is good or poor conductor?Sol:-By the use of tester Tester:-It is the instrument that can test that given substance is conducting and non conducting.Activity showing how to check that tester is working or not?
Join free ends of a tester together, This joining will complete the circuit
If bulb will glow then tester is working otherwise tester is not working
Do liquid conduct electricity?
Sol:- to test take any liquid say lemon juice in a beaker.
Adjust the apparatus as show in figure.
(i) To check if the liquid is conducting or not, connect the liquid between the two ends of tester by completing the connection of the circuit properly.
Testing conduction of electricity in liquid
(ii) Most liquids that conduct electricity are solutions of acids, bases and salts.
Heating effect of current:
The heating effect of current is responsible for the glowing of the bulb.
To test whether substance is conducting or not using heating effect:-Due to the heating effect of current the filament of bulb gets heated to a high temperature and it starts glowing. But, if current is very small then the filament will not get heated sufficiently and so will not glow.
How to check the weak current in circuit? LED (Light Emitting Diodes)
LED’s can be used to detect weak currents, since; their filament does not require much temperature to glow.
They have two terminals called called leads attached to an LED. One lead is longer (Anode) and other is slightly short (Cathode). Longer lead is always connected to the positive terminal of the battery. On the hand, Shorter lead and is connected to the negative terminal of the battery.
LED
Magnetic effect of current:
The magnetic effect of current is responsible for the deflection in magnetic compass when current passes nearby it. It can detect weak currents.
To test whether substance is conducting or not using magnetic effect:
For a closed circuit, when current passes nearby a magnetic needle and if the deflection is observed in the needle then it means the substance is conducting; otherwise it is non-conducting.
Magnetic Compass
Tester By using Magnetic Compass:
(i) Take the tray from inside a blank matchbox.
(ii) Wrap an electric wire a few times around the tray.
(iii) Insert a small compass needle inside it.
(iv) Now connect one free end of the wire to the terminal of a battery. Leave the other end free.
(v) Take another piece of wire and connect it to the other terminal of the battery
Tester by using the magnetic compass
Join the free ends of two wires momentarily. The compass needle should show deflection. Your tester with two free ends of the wire is ready.
Touch the both ends of tester to any substance to check whether the substance is conducting the electricity or not. If the deflection is observed in the needle then it means the substance is conducting; otherwise it is non-conducting.
Tap Water:
The water obtained from various sources like rivers, wells, taps, etc. is not in its purest form. It contains many impurities in it. These impurities include different salts too. As a result of these salts, the tap water becomes a good conductor of electricity.
Distilled Water:
It is the purest form of water and does not contain any kind of impurities in it. Hence, it is a poor conductor of electricity.
Distill Water
We can check the conductivity of tap water or distill water via the magnetic tester.
Chemical Effects of Electric Current: -The chemical changes that takes place when an electric current passes through ionic solution is called chemical effect of electric current.
Electrodes:
These are conducting materials through which current enters or leaves a substance.
Types of Electrodes:
(i) Positive Electrode: It is the electrode which is connected to the positive terminal of the battery. It is also known as Anode.
(ii) Negative Electrode: It is the electrode which is connected to the negative terminal of the battery. It is also known as Cathode.What is an electrolyte?A solution that breaks into its ions on passing electricity through it is called an electrolyte. Electrolytes are used in the process of electroplating.
What are an anode and cathode?
The positively charged electrode is called anode and the negatively charged electrode is called cathode.
What are anions and cations?
An anion is a negatively charged ion and a cation is a positively charged ion.
There can be various chemical effects observed on passing electric current depending on the type of solution and electrodes:
1. Formation of Gas Bubbles:
A British Chemist named William Nicholson performed an experiment showing that if current is passed through water, then, bubbles of oxygen and hydrogen were produced. The oxygen bubbles will be present on positive electrode and hydrogen bubbles on the negative electrode. The passage of an electric current through a conducting solution causes chemical reactions. As a result, bubbles of a gas may be formed on the electrodes
2. Deposits of metal may be visible on the electrodes.
3. The color of solution might change.
William Nicholson
Passing current through water
Electroplating:
The process using which layer of some metal is deposited on another material by using electricity is known as electroplating.
Experiment: We need to take copper sulphate and two copper plates of same size. Take 250 mL of distilled water in a clean and dry beaker. Dissolve two teaspoonful of copper sulphate in it. Add a few drops of dilute sulphuric acid to copper sulphate solution to make it more conducting. Connect the copper plates to the terminals of a battery and immerse them in copper sulphate solution.
Connect the circuit as shown in the figure.
When current is allowed to pass through the copper sulphate solution, then the solution will separate into the copper and sulphate. The separated free copper of the solution will get deposited on the negative electrode. And the same amount of copper will get dissolved in the solution from the positive electrode. Hence, we can say that copper from positive electrode got transferred to the negative electrode. This kind of transfer is known as electroplating.
Applications of Electroplating:
(i) It is used in industries for coating different metals on other metal objects. For example, chromium which is a lustrous, corrosion free, scratch resistant, etc. but being costly is deposited on materials like car parts, taps, burners, etc. to lower the manufacturing cost.
(ii) Silver and gold are deposited on cheaper materials by jewelers to lower the jewellery cost, but, keeping the appearance intact.
(iii) Iron cans are electroplated with tin used for storing food, as iron gets easily rusted and so protects the food from spoiling.
(iv) Zinc is deposited on iron used for the construction of bridges, vehicles, etc. to protect it from rust and corrosion.
