Ans: The electricity which is possessed due to the flow of charges in bodies is called current electricity.
2. What is an electric charge?
Ans: The electrical property of a particle of a body is called an electric charge.
3. What is an electric charge?
Ans: The electrical property of a particle of a body is called an electric charge.
4. What is cell?
Ans: A cell is a device which converts chemical energy into electrical energy.
5. What are primary cells?
Ans: The cells which cannot be recharged are called primary cells.
6. What is an open circuit?
Ans: An electrical circuit through which no electricity flows is called an open circuit.
7. What is polarization?
Ans: The defect of a simple cell due to the formation of layer of hydrogen bubbles on the copper plate is called polarization.
8. What is leclanche cell?
Ans: An improved form of simple cell in which MnO2 is used as a depolarizer is called leclanche cell.
9. What is a fuse?
Ans: A circuit breaker with low melting point and high resistivity is called a fuse.
10. What are conductors?
Ans: The substances through which the electric current passes are called conductors.
11. What is static electricity?
Ans: The electricity which is possessed by the change in the number of electrons in bodies is called static electricity.
12. What is an insulator?
Ans: The substance which does not allow electric current to pass through it is called insulator.
13. What is a semi- conductor?
Ans: The substance which allows electric current to pass through it partially is called semi- conductor.
14. What is a closed circuit?
Ans: The electric circuit through which current flows is called closed circuit.
15. What is conventional direction of current?
Ans: The representation of flow of charge from positive to negative is called conventional direction of current.
16. What is fuse wire?
Ans: A short piece of wire having low melting point is called fuse wire.
17. What is parallel combination of cells?
Ans: If the positive terminals of all cells are connected at one side and the negative terminals at the other side, it is called parallel combination of cells.
18. What is parallel combination of cells?
Ans: If the positive terminals of all cells are connected at one side and the negative terminals at the other side, it is called parallel combination of cells.
19. What is series combination of cells?
Ans: If the positive terminal of one cell is connected with the negative terminal of the second and so on, it is called series combination of cells.
20. What is mixed combination of cells?
Ans: When both of the parallel and series combination of cells are used in a combination, it is called mixed combination of cells.
21. What is short circuit?
Ans: The circuit in which positive and negative terminals of a cell are directly connected to each other is called short circuit.
22. Name the cathode, anode and electrolyte in a dry cell. Write any three properties of a magnet.
Ans: In a dry cell,
cathode = carbon
anode = zinc
electrolyte = ammonium chloride
Any three properties of a magnet are:
a. A freely suspended bar magnet always points North-South direction.
b. Magnetic poles cannot be isolated.
c. Like poles of a magnet repel while its unlike poles attract.
23. Write any three reasons of using dry cell in a torch light.
Ans: The reasons of using dry cell in a torch light are:
i. They are compact and portable.
ii. They are cheaper to manufacture.
iii. They are found in variable shapes and sizes.
24. What is electricity? Write two defects of simple cell.
Ans: Electricity is a type of energy fueled by the transfer of electrons from negative and positive points with a conductor.
The two defects of simple cell are:
i. Polarization
ii. Local action
25. What type of combination of loads is used in domestic wiring? Write two advantages of this type of combination. In which wire should we connect switch?
Ans: Parallel type of combination of loads is used in domestic wiring.
The two advantages of parallel type of combination are:
i. They can be conducted independently by an individual switch.
ii. They ensure all components in the circuit have the same voltage as the source.
We should connect switch in neutral wire.
26. Polarization does not take place in dry cell, why? Write two advantages of using MCB in a house.
Ans: Polarization does not take place in dry cell because manganese dioxide that is rich in oxygen is used in dry cell which supplies free oxygen to combine with the hydrogen and form water and prevents from forming hydrogen bubbles on the surface of the anode.
The advantages of using MCB in a house are:
i. MCB is quick work against short circuit.
ii. It works quickly on overloading and under voltage.
27. What is an electric cell? How many types of cell are there?
Ans: A cell is a device which maintains a potential difference between the positive and the negative terminals. Cells convert chemical energy into electrical energy.
There are two types of cells namely:
a) Primary Cell
b) Secondary Cell
28. What is static electricity? Give some examples of static electricity.
Ans: Static electricity is the electricity that does not move. The word ‘static’ means standing still. Therefore, static electricity refers to electrical charges that remain on materials.
For example:
a) A balloon rubbed with wool attracts paper.
b) A plastic comb rubbed against dry hair attracts small pieces of paper.
29. Define Conductors and insulators.
Ans: Those substances through which electrons can pass are known as conductors. There are two types of conductors:
a. Good Conductors: Iron, Copper, Aluminuium etc.
b. Bad Conductors: Human Body, wet piece of wood, water etc.
Whereas, insulators are those substances which do not favors the transfer of electrons through them. Insulators are used to prevent the unnecessary flow of electric current. Example: Ceramic, rubber, plastics, wood etc.
30. Write down advantages of dry cell.
Ans: Some of the advantages of dry cell are as follows:
a) They are compact and portable.
b) They do not contain liquid which otherwise could spill.
c) They are cheaper to manufacture.
d) They are found in variable shapes and sizes.
31. What is combination of cells? How many types of cell combinations are there?
Ans: A single cell is unable to give a desired current or voltage, so two or more cells are used together. This grouping of two or more cells together in a circuit is called combination of cells.
The cells are usually combined in two ways. They are:
a) Series Combination
b) Parallel Combination
32. Why do we hear crackling sound while taking off our sweaters?
Ans: Woolen or synthetic sweaters develop static charges (electrons) on them due to friction. While taking off our sweater, these charges move in streams between the sweater and our body, i.e. electric discharge takes place. This results in crackling sound and tiny sparks of lightning.
33. There is no polarization in a dry cell. Why?
Ans: The carbon rod in the dry cell is surrounded by a compressed mixture of carbon powder and manganese dioxide (MnO2) which acts as a depolarizing agent. Hence, there is no polarization in a dry cell.
34. Explain colour coding in wires in brief.
Ans: Electrical appliances such as TV, electric iron, etc. have three core flexible cables, which have different colour insulation. This is known as the colour coding of wires.
If all the wires have same colour of insulation, it will be difficult to locate the two ends of any wire.
Colour coding has the following advantages:
i. It makes easy to identify the type of wire in underground wiring.
ii. It makes easy to identify the phase (live), neutral and earth wire.
Colour convention given to wires:
Wire | Old Convention | New International Convention |
Live | Red | Brown |
Neutral | Black | Light Blue |
Earth | Green | Green and Yellow |
35. Define conventional and actual direction of current with figure.
Ans: Before 18th century the scientists thought that charge (electrons) flows from positive terminal to negative terminal. But it has been revealed that the charge flows from negative terminal to positive terminal. The representation of flow of charge from positive to negative terminal is called conventional direction of current and the representation of flow of charge from negative to positive terminal is called actual direction of current. The direction of current flow in both cases is shown in figure below:
36. Differentiate between Series and Parallel combination.
Ans: The difference between series and parallel combination are as follows:
Series Combination | Parallel Combination |
1. When positive terminal of one cell is connected to the negative terminal of the next cell and so on, the cells are said to be connected in series. | 1. When positive terminals of every cell are connected together and negative cells are connected together in a cell, then we call the cells as parallel cells |
2. The total voltage is equal to the sum of voltage of the individual cells. i.e. V= V1+V2+V3 | 2. The total voltage does not increase. The total voltage is equal to the voltage of a single cell. V=V1=V2=V3 |
3. In a series circuit, the current through each of the components is the same. i.e. I=I1=I2=I3 | 3. The total current is equal to the sum of the current through single cell. i.e. I = I1+I2+I3 |
4. The bulb glows for a short time in this type of combination. | 4. The bulb glows for a longer time in this type of combination. |
37. Differentiate between Static Electricity and Current Electricity.
Ans: The differences between static and current electricity are as follows:
Static Electricity | Current Electricity |
1. It is caused due to the change in number of electrons in bodies. | 1. It is caused due to flow of electrons in bodies. |
2. It is produced in insulators. | 2. It occurs in good conductors. |
3. It cannot be transported from place to place through conducting wires. | 3. It can be transported from place to place through conducting wire. |
4. It has no useful work in our daily life. | 4. It is useful in our daily life. |
38. What is a simple cell? Explain with figure.
Ans: A simple cell is called a voltaic cell. It is used to get small current. It consists of a vessel containing dilute sulphuric acid with a copper plate and a zinc plate dipped in it. The two metals act differently in the presence of the acid and a potential difference of about 1 volt is developed. The metal plates are called electrodes and the dilute acid is called the electrolyte. The copper plate is at higher potential and is called the positive electrode. The zinc plate is at low potential and is called the negative electrode.
When two plates are connected by wire, the bulb connected in it glows. The bulb does not glow for a long time because it has two defects. They are polarization and local action.
39. What is a dry cell? How is a dry cell made?
Ans:
A dry cell is a portable cell. A dry cell consists of a zinc container whose base acts as the negative electrode. The carbon rod placed at the centre with a brass cap (metal cap) acts as the positive electrode. This is surrounded by a mixture of manganese dioxide and charcoal in a muslin bag. The electrolyte uses is a moist paste of ammonium chloride. The outer body (excluding the base) of the zinc container is insulated with cardboard.
When the dry cell is connected in a circuit comprising a bulb, current flows in the circuit due to the chemical reaction that takes place in the cell. This makes the bulb glow. The dry cell is a primary cell and it cannot be recharged.
40. Write short notes on fuse.
Ans: A fuse is a safety device which is made of thin wire with high resistance and a low melting point. It is an alloy of tin and lead and is always connected in the live wire. If current flowing through it is more than the required amount, it gets heated and melts breaking the circuit.
The capacity of the fuse used should be slightly more than the maximum current that flow over it. If a fuse of lower rating than the required is used, it will blow out unnecessarily. If the fuse of much higher rating is used then the appliances becomes unsafe because more electric current flows through it resulting the damage of appliance and also risk of fire in some cases. Thus, the fuse of nearest high value should be used.
41. What is polarization? How can it be minimized?
Ans: During chemical reaction hydrogen bubbles gather around the copper plate. These bubbles behave as insulator and prevent the flow of current. This effect is known as polarization.
Methods to minimize polarization are:
a) The mechanical method of removing polarization is to take out copper and brush it several times to remove the layer of hydrogen.
b) The chemical method is to use depolarizer such as potassium dichromate (K2Cr2O7) which oxidizes hydrogen to water.
42. Differentiate between: Fuse Wire and Simple Wire.
Ans: The differences between fuse wire and simple wire are as follows:
Fuse Wire | Simple Wire |
1. It is a short piece of wire having low melting point. | 1. It is a long piece of wire having high melting point. |
2. It is a thin wire of an alloy of tin and lead. | 2. It is a wire available in variable size and is made of copper, aluminium, silver etc. |
3. It is a safe device and melts when excess current flows in the circuit. | 3. It is an agent through which current flows from one point to another through the circuit. |
4. It has higher resistivity. | 4. It has lower resistivity. |
43. Differentiate between Simple and Dry Cell.
Ans: The differences between simple and dry cell are:
Simple Cell | Dry Cell |
Dilute sulphuric acid is used as an electrolyte. | Ammonium chloride paste is used as electrolyte. |
A zinc plate is used as negative electrode and copper as a positive. | A zinc container is used as negative electrode and a carbon rod as positive electrode. |
Two defects of simple cell are local action and polarization. | Polarization is prevented by depolarizer but local action exists. |
It is not compact and portable. | It is compact and portable. |
44. Differentiate between: Open Circuit and Closed Circuit.
Ans: The differences between open and closed circuit are as follows:
Open Circuit | Closed Circuit |
1. An electrical circuit through which no current flows is called an open circuit. | 1. An electrical circuit through which electrical current flows is called closed circuit. |
2. In open circuit potential difference is not established. | 2. Potential difference is established in closed circuit. |
3. Open circuit is represented by the symbol: | 3. Closed circuit is represented by the symbol: |
45. What is electrical current? Write its SI unit and its relation with charge.
Ans: Electric current is defined as the rate of flow of charge.
The SI unit of electric current is Ampere (A).
The relation between electric current and charge is given by the formula:
46. A balloon rubbed on woolen clothes stick to walls. Why?
Ans: The balloon rubbed against woolen clothes collects negative electrical charge on its surface. When the balloon is brought near to the wall it attracts positive charge. This attraction of positive and a negative charge makes the balloons rubbed on woolen clothes stick to the wall.
