NCERT-Solutions-Class-6-Science-Electricity and Circuits
NCERT notes along with solutions for class 6: science – Chapter “Electricity and Circuits” are provided here. The notes as well as solutions are very much helpful for the students to understand the topic. The solutions will be handy for quickly completing the homework and preparing for exams.
Electricity is a type of energy that power many things that we use daily in our life like televisions, geysers, fans, refrigerators, music systems etc. We use electricity on a large scale to lip up street lights, to run machines in factories, to run trains, metros etc.
Have you ever wondered from where do you get this electricity? How does this electricity work? Come on, let us descend into this lesson to learn more about electricity.
Electricity
Electric current is the amount of charge that flows past a point in a circuit or through a component in a given time period i.e. the rate of flow of charge.
The formula of electric current = charge/ time
Or I = Q/ T
Where, I = current (in Ampere)
q = charge (in coulomb)
t = time taken (in seconds)
Sources of electricity
The major sources of electricity are: thermal power, hydel power, wind power, solar power, tidal power etc. Apart from these sources of electricity, we also get small amount of electricity from cells or batteries for running our small appliances like torch, radio, TV remote, clock etc.
Electric Cell
- An electric cell is a device that converts chemical energy into electrical energy. It produces electricity from the chemicals stored inside it.
- The main components of electric cells are the anode (negative electrode, where oxidation takes place) and the cathode (positive electrode, where reduction takes place).
- Electric cells work on the fundamental principle of redox reaction (a combination of reduction and oxidation). The resulting electron flow from the anode to the cathode generates an electric current.
- Different electric cells use different materials as the anode and cathode, which influences their performance, application and energy output.
- All electric cells have two terminals labelled as (+) and (-) on it. The metal cap is the positive terminal whereas the metal disc is the negative terminal.
Types of Electric Cell
- Primary Cells – It cannot be recharged. So it can be used only once. cells used in clocks, watches, toys, etc., are generally primary cells.
- Secondary Cells – A cell that can be recharged many times is called a secondary cell. These cells are also called storage cells or accumulators. Secondary Cells are used in Mobile phones, laptops, emergency lamps and vehicle batteries.
Chemical Reaction in Electric Cell
- The chemical reaction inside the cell tends to push electrons to one electrode (creating an excess) and away from the other electrode (generating a deficit).
- The electrode with electron excess acquires a negative charge and becomes the anode, while the electrode with electron deficit acquires a positive charge and becomes the cathode.
- When a wire joins the anode and cathode externally (forming an electric circuit), electrons flow from the anode to the cathode through the wire, creating an electric current.
Battery
A battery is a collection of cells.
Electric Circuit
- The path along which electric current flows is called an electric circuit. In an electric circuit, electric current flows from the positive terminal to the negative terminal of the battery.
A circuit generally has:
a) A cell or a battery- a source of electric current
b) Connecting wires- for carrying current
c) A bulb- a device that consumes the electricity
d) A key or a switch- this may be connected anywhere along the circuit to stop or allow the flow of current.
Symbols for some electric circuit components
Types of Circuit
Series and Parallel Connection
In an electric circuit or arrangement, its components can be connected in two different ways. One is called a parallel connection and the other is called a series connection.
Series Connection
- In a series circuit there is a single loop, the current has only one path to take.
- In a series connection, the current is same in all the components.
- In a series connection, the potential difference is shared between the components.
- In a series connection, the total resistance is the sum of the individual resistances of the components.
- In series connection, a break in one component ruins the whole circuit.
Point to be noted when bulbs are connected in series
- In series circuit, all bulbs work when the circuit is closed or all bulbs stop working when the circuit is open. If any one of the bulbs gets fused, then the other bulbs also stop working.
- In series connection, the bulbs do not glow brightly. In this case the electrical energy drawn from the battery is shared by all the bulbs connected in series. In fact, when connected in series, the appliances do not work to their capacity.
Parallel Connection
A parallel connection is a branched electrical system with multiple paths (branches) for the current to flow along.
The following points are to be noted about the bulbs connected in parallel.
1. All the bulbs are connected directly to a battery, and hence, work independently. Even if one bulb is fused out, the remaining bulbs work normally.
2. All the bulbs derive the required electrical energy and glow brightly.
3. Potential difference (PD) is the same across all branches.
PD of power supply=PD of each branch
4. Current is shared between each of the branches.
Current through source=sum of current through each branch
5. The total resistance of two resistors in parallel is less than the resistance of the smallest individual resistor.
Points to be noted when bulbs are connected in parallel
- All the bulbs are connected directly to a battery, and hence, work independently. Even if one bulb is fused out, the remaining bulbs work normally.
- All the bulbs derive the required electrical energy and glow brightly.
Electric Switch
- An electric switch is a device used to close or open an electric circuit. A switch in a circuit can be placed anywhere.
- When the switch is in the ‘ON’ position, the circuit from the positive terminal of the battery to the negative terminal is complete. The circuit is then said to be closed and the current flows through out the circuit instantly.
- When the switch is in the ‘OFF’ position, the circuit is incomplete. It is said to be open and no current flows through any part of the circuit. Thereby the electric bulb will not glow.
Electric Conductors
The materials which allow electric charges to pass through them are called conductors. For example: Copper, iron, aluminium, impure water, earth etc.
Insulators
The materials which do not allow electric charges to pass through them are called insulators or non-conductors. For example: plastic, glass, wood, rubber, china clay, ebonite etc.
Solution of the Exercise
1. Fill in the blanks
(a) A device that is used to break an electric circuit is called ________.
(b)An electric cell has______ terminals.
Solution
(a) switch
(b) two
2. Mark "True" or "False" for following statements:
(a) Electric current can flow through metals.
(b) Instead of metal wires, a jute string can be used to make a circuit.
(c)Electric current can pass through a sheet of thermocol.
Solution:
(a) True (Metals are good conductors of electricity.)
(b) False (Jute is a bad conductor of electricity. Hence, strings made of Jute cannot be used to make a circuit.)
(c) False (Electric current cannot pass through a sheet of thermocol because thermocol is a bad conductor of electricity.)
3. Explain why the bulb would not glow in the arrangement shown in Fig. 9.13.
Answer:
The back part of the tester is made up of plastic which is an insulator and it does not allow electricity to pass through it. So, electricity will not flow from one terminal to the other terminal of the tester. As a result, the bulb will not glow.
4. Complete the drawing shown in Fig. 9.14 to indicate where the free ends of the two wires should be joined to make the bulb glow.
Answer:
The black wire should be connected to the bottom of the bulb and the green wire should be connected to one end of the cell as shown in the picture given below to make the bulb glow.
5. What is the purpose of using an electric switch? Name some electrical gadgets that have switches built into them.
Answer:
The main purpose of using an electric switch is either to break the electric circuit or complete it. Hence, by turning the electric switch in “ON” or “OFF” mode, we can use the appliances or machines according to our desire. Some electric gadgets that have switches built into them are: TV, Refrigerator, Toaster, Washing Machine etc.
6. Would the bulb glow after completing the circuit shown in Fig.9.14 if instead of safety pin we use an eraser?
Answer:
No, the bulb will not glow if we use an eraser because an eraser is an insulator. And we all know that an insulator does not allow electric current to pass through it. Whereas, a safety pin is made up of a metal which is a good conductor of electricity and in this case the bulb will glow.
7. Would the bulb glow in the circuit shown in Fig.9.15?
Answer:
The bulb will not glow. If we closely look at the connection of the two wires with the bulb we will find that both the wires – blue wire as well as red wire, are connected with only one terminal of the bulb which makes the circuit incomplete or incorrect. A bulb has two terminals. One terminal is present at the side lower part of the bulb whereas the second terminal is present at the bottom of the bulb. For the bulb to glow, one wire (either blue or red) should be connected to one terminal (side lower part) of the bulb and the other wire should be connected to the second terminal (bottom) of the bulb.
8. Using the "Conduction Tester" on an object it was found that the bulb begins to glow. Is that object a conductor or an insulator? Explain.
Answer:
Since the bulb begins to glow, it tells that the object allows current to pass through itself. And we know that a conductor allows electric current to pass through itself. Hence, the object is a conductor not an insulator.
9. Why should an electrician use rubber gloves while repairing an electric switch at your home? Explain.
Answer:
A rubber gloves is an insulator. So, it also does not allow electric current to pass through it. Knowing this property of rubber gloves, an electrician generally uses rubber gloves while repairing an electric switch to prevent his body from electric shocks.
10. The handles of the tools like screwdrivers and pliers used by electricians for repair work usually have plastic or rubber covers on them. Can you explain why?
Answer:
Plastic or rubber covers are insulators which means that these things do not allow electric current to pass through them. So, the handles of the tools like screwdrivers and pliers used by electricians usually have plastic or rubber covers on them to prevent the electrician from electric shocks.