1. Under what condition does an electric current produce a magnetic effect?
Answer:
The magnetic effect is observed only when electric current is flowing through a conductor.
2. Name the scientist associated with the discovery of the magnetic effect of electric current.
Answer:
Hans Christian Ørsted discovered the relationship between electricity and magnetism.
3. What does the movement of a compass needle placed near a current-carrying wire indicate?
Answer:
It indicates that a magnetic field is produced around the current-carrying wire.
4. What is an electromagnet?
Answer:
An electromagnet is a temporary magnet produced when electric current flows through a coil of wire.
5. Why does an electromagnet lose its magnetic property when the switch is turned off?
Answer:
When the switch is turned off, the current stops flowing through the coil. Therefore, the magnetic field disappears.
6. Mention two methods of increasing the strength of an electromagnet.
Answer:
The strength of an electromagnet can be increased by:
* Increasing the number of turns of the coil.
* Placing a soft iron core inside the coil.
7. What happens to the poles of an electromagnet if the direction of current through its coil is reversed?
Answer:
The north and south poles interchange. The north pole becomes the south pole and vice versa.
8. Why are electromagnets useful for lifting heavy pieces of iron or steel?
Answer:
Their magnetism can be controlled. They can be switched on to lift the load and switched off to release it.
9. Where are lifting electromagnets commonly used?
Answer:
They are commonly used in scrap yards for lifting and moving heavy iron and steel objects.
10. State one important difference between a permanent magnet and an electromagnet.
Answer:
A permanent magnet possesses magnetism continuously, whereas an electromagnet acts as a magnet only when electric current flows through it.
11. On which factors does the heating effect of electric current depend?
Answer:
The heating effect depends on factors such as:
* The resistance of the conductor.
* The amount of current flowing.
* The duration for which current flows.
12. Why is nichrome commonly used in heating appliances?
Answer:
Nichrome has high electrical resistance. Therefore, it produces a significant heating effect when electric current passes through it.
13. How does higher resistance affect the heat produced in a conductor?
Answer:
For the same current and time, a conductor with greater resistance produces more heat.
14. Why is the heating element of an electric appliance made from a material having high resistance?
Answer:
A high-resistance material converts more electrical energy into heat, making it suitable for heating appliances.
15. How is electricity produced in a voltaic cell?
Answer:
Electricity is produced due to chemical reactions involving the electrodes and the electrolyte.
16. What material forms the outer container of a dry cell?
Answer:
The outer container of a dry cell is made of zinc.
17. Which terminal of a dry cell is associated with the zinc container?
Answer:
The zinc container acts as the negative terminal.
18. What is the central rod of a dry cell made of?
Answer:
The central rod is made of carbon.
19. What is the function of the carbon rod in a dry cell?
Answer:
The carbon rod acts as the positive terminal of the dry cell.
20. In what physical form is the electrolyte present inside a dry cell?
Answer:
The electrolyte is present in the form of a thick paste.
21. What are rechargeable cells generally called?
Answer:
Rechargeable cells are called secondary cells.
22. Why are ordinary non-rechargeable cells called primary cells?
Answer:
They are called primary cells because they are generally used until their stored chemicals are exhausted and cannot be recharged for repeated use.
23. What happens to the capacity of a rechargeable battery after repeated charging and use, according to the transcript?
Answer:
Its capacity gradually decreases after many recharge cycles.
24. When do we say that a battery has become dead?
Answer:
A battery is considered dead when the chemicals required for the chemical reaction have been used up and it can no longer produce electricity.
25. A crane lifts a large quantity of iron scrap and then releases it at another location. Why is an electromagnet more suitable than a permanent magnet for this purpose?
Answer:
An electromagnet can be switched on to attract and lift the iron scrap. Once the material reaches the required location, the current can be switched off, causing the magnetic effect to disappear and the load to be released.
26. What common property is shared by a permanent magnet and a lifting electromagnet?
Answer:
Both can attract magnetic materials.
27. Can both a permanent magnet and an electromagnet be switched off? Explain.
Answer:
No. An electromagnet can be switched off by stopping the electric current. A permanent magnet cannot normally be switched off because it possesses permanent magnetism.
28. A coil initially has end A as the north pole and end B as the south pole. What will happen when the current direction is reversed?
Answer:
End A will become the south pole, while end B will become the north pole.
29. A student wants to make an electromagnet stronger without changing its basic arrangement. What modification can the student make to the coil?
Answer:
The student can increase the number of turns of the wire in the coil.
30. Why is a fuse connected as a safety device in an electric circuit?
Answer:
A fuse protects the circuit by melting when excessive current flows. This breaks the circuit and prevents possible damage to electrical appliances and wiring.
31. A compass needle is placed close to a wire. It remains undeflected when the circuit is open but moves when the switch is closed. What conclusion can be drawn?
Answer:
The current flowing through the wire produces a magnetic field, which causes the compass needle to deflect.
32. Why is an electromagnet described as a temporary magnet?
Answer:
Its magnetic property exists only while electric current flows through its coil. When the current stops, the magnetism disappears.
33. A scrap-yard operator needs to pick up metal pieces and release them repeatedly. Which property of an electromagnet makes this operation possible?
Answer:
Its magnetic strength can be controlled by controlling the flow of electric current.
34. What would happen if the number of turns in an electromagnet's coil were increased?
Answer:
The electromagnet would become stronger because increasing the number of turns increases its magnetic effect.
35. Why does a fuse create an open circuit during an electrical overload?
Answer:
During excessive current flow, the fuse wire melts. This breaks the conducting path and stops the flow of current through the circuit.
The following MCQs are based on the concepts discussed in the transcript. The questions have been written in fresh wording and are entirely in English.
1. A compass needle changes its direction when placed close to a wire carrying current. This happens because the wire produces:
A. gravitational force
B. a magnetic field
C. chemical energy
D. light energy
Answer: B. a magnetic field
2. An electromagnet behaves like a magnet only when:
A. it is heated
B. it is cooled
C. electric current flows through it
D. it is placed near a permanent magnet
Answer: C. electric current flows through it
3. What happens to an electromagnet when the electric current is switched off?
A. Its strength increases
B. Its magnetic property disappears
C. Its poles become permanent
D. It starts producing more heat
Answer: B. Its magnetic property disappears
4. The poles of an electromagnet can be reversed by:
A. increasing the number of turns
B. increasing the length of the wire
C. reversing the direction of current
D. removing the coil
Answer: C. reversing the direction of current
5. Which of the following is a property of a permanent magnet?
A. Its magnetism exists only when current flows.
B. Its poles can be changed by reversing current.
C. It remains magnetic without an electric supply.
D. It can be switched on and off easily.
Answer: C. It remains magnetic without an electric supply
6. Which change can make an electromagnet stronger?
A. Decreasing the number of turns in the coil
B. Increasing the number of turns in the coil
C. Disconnecting the current supply
D. Removing the conducting wire
Answer: B. Increasing the number of turns in the coil
7. The strength of an electromagnet can also be increased by:
A. decreasing the current
B. increasing the current
C. reversing the current continuously
D. removing the power source
Answer: B. increasing the current
8. Nichrome is commonly used in heating elements mainly because it has:
A. very low resistance
B. high resistance
C. no resistance
D. magnetic properties
Answer: B. high resistance
9. When current passes through a nichrome wire, electrical energy is mainly converted into:
A. chemical energy
B. nuclear energy
C. heat energy
D. gravitational energy
Answer: C. heat energy
10. Heating appliances should not be kept switched on unnecessarily for a long time because:
A. they stop conducting electricity
B. electricity and energy may be wasted, and overheating may occur
C. they become permanent magnets
D. their resistance becomes zero
Answer: B. electricity and energy may be wasted, and overheating may occur
11. Excessive heating of an electrical appliance can increase the possibility of:
A. magnetic levitation
B. fire and accidents
C. freezing
D. loss of gravity
Answer: B. fire and accidents
12. Which feature is common to both a voltaic cell and a dry cell?
A. Both contain a liquid electrolyte.
B. Both have only one electrode.
C. Both convert chemical energy into electrical energy.
D. Both are rechargeable.
Answer: C. Both convert chemical energy into electrical energy
13. The electrolyte in a typical dry cell is present mainly in the form of:
A. a solid metal sheet
B. a paste
C. a gas
D. pure water
Answer: B. a paste
14. In a voltaic cell, the electrolyte is generally:
A. in liquid form
B. absent
C. in the form of a metal cap
D. a permanent magnet
Answer: A. in liquid form
15. In a dry cell, the zinc container acts as the:
A. positive terminal
B. negative terminal
C. insulating layer only
D. heating element
Answer: B. negative terminal
16. The carbon rod in a dry cell is associated with the:
A. negative terminal
B. positive terminal
C. fuse connection
D. outer insulating cover
Answer: B. positive terminal
17. What is the main purpose of a fuse or an MCB in a household circuit?
A. To increase the current continuously
B. To generate electricity
C. To protect the circuit from excessive current
D. To convert electricity into chemical energy
Answer: C. To protect the circuit from excessive current
18. A fuse protects an electrical circuit by:
A. increasing its resistance permanently
B. melting and breaking the circuit during excessive current
C. producing a magnetic field
D. storing electrical energy
Answer: B. melting and breaking the circuit during excessive current
19. What does an MCB generally do when excessive current flows through a circuit?
A. It stores the extra current.
B. It automatically breaks the circuit.
C. It converts the current into chemical energy.
D. It increases the voltage.
Answer: B. It automatically breaks the circuit
20. Transmission wires are made of low-resistance materials mainly to:
A. increase heating
B. reduce energy loss during transmission
C. produce stronger magnets
D. store electrical energy
Answer: B. reduce energy loss during transmission
21. Why are electric transmission wires generally made thick?
A. To increase their resistance
B. To reduce energy loss and allow smooth current flow
C. To make them act as electromagnets
D. To increase the heating effect
Answer: B. To reduce energy loss and allow smooth current flow
22. A dead ordinary dry cell generally cannot be recharged because:
A. it has no electrodes
B. it is designed as a non-rechargeable cell
C. it contains a permanent magnet
D. it has very low resistance
Answer: B. it is designed as a non-rechargeable cell
23. When the chemicals of a dry cell are used up, the cell:
A. becomes an electromagnet
B. starts producing more electricity
C. becomes dead
D. becomes rechargeable
Answer: C. becomes dead
24. Which type of battery is generally used in devices such as mobile phones and laptops?
A. A non-rechargeable dry cell
B. A rechargeable battery
C. A fuse cell
D. A magnetic cell
Answer: B. A rechargeable battery
25. Why are electromagnets preferred over permanent magnets in scrap-handling operations?
A. They are always magnetic.
B. Their magnetism can be switched on and off.
C. They do not require electricity.
D. They cannot attract iron.
Answer: B. Their magnetism can be switched on and off
26. In a scrap yard, an electromagnet can release the lifted metal when:
A. the current is switched off
B. the current is increased
C. the number of turns is increased
D. it is connected to a fuse
Answer: A. the current is switched off
27. Which component forms the outer zinc container of a dry cell?
A. Positive terminal
B. Negative terminal
C. Carbon electrode
D. Metal cap of the positive terminal
Answer: B. Negative terminal
28. The paste electrolyte in a dry cell may contain:
A. sodium chloride and copper
B. ammonium chloride and manganese oxide
C. iron and aluminium
D. zinc and carbon only
Answer: B. ammonium chloride and manganese oxide
29. Which of the following is an advantage of rechargeable batteries?
A. They can be used only once.
B. They can be reused after charging.
C. Their capacity increases indefinitely.
D. They are always lighter than disposable cells.
Answer: B. They can be reused after charging
30. Which is a limitation of rechargeable batteries ?
A. They cannot produce electricity.
B. Their capacity may decrease after repeated charging cycles.
C. They have no electrodes.
D. They cannot be used in electronic devices.
Answer: B. Their capacity may decrease after repeated charging cycles
31. Compared with disposable cells, rechargeable batteries may:
A. become lighter after every use
B. have a higher initial cost
C. never wear out
D. be impossible to reuse
Answer: B. have a higher initial cost
32. Which of the following is an environmental advantage of rechargeable batteries?
A. They increase electrical resistance.
B. They can be reused, reducing battery waste.
C. They produce permanent magnetism.
D. They eliminate the need for electricity.
Answer: B. They can be reused, reducing battery waste
33. The two main effects of electric current discussed are:
A. chemical and nuclear effects
B. magnetic and heating effects
C. gravitational and optical effects
D. cooling and sound effects
Answer: B. magnetic and heating effects
34. Which of the following demonstrates the magnetic effect of electric current?
A. An electric iron becoming hot
B. An electromagnet attracting iron
C. A dry cell becoming dead
D. A fuse melting due to excessive current
Answer: B. An electromagnet attracting iron
35. Which appliance is an example of the heating effect of electric current?
A. Electromagnet
B. Compass needle
C. Electric iron
D. Permanent magnet
Answer: C. Electric iron
36. A cell that cannot normally be recharged is called a:
A. secondary cell
B. primary cell
C. magnetic cell
D. heating cell
Answer: B. primary cell
37. A rechargeable cell is classified as a:
A. primary cell
B. secondary cell
C. dry conductor
D. permanent cell
Answer: B. secondary cell
38. Which of the following is an example of a secondary cell mentioned ?
A. A dry cell used in a remote
B. A rechargeable mobile phone battery
C. A fuse wire
D. A compass needle
Answer: B. A rechargeable mobile phone battery
39. Why are dry cells easier to carry than traditional voltaic cells?
A. They contain a paste-like electrolyte that reduces leakage problems.
B. They have no electrolyte.
C. They produce unlimited electricity.
D. They are permanent magnets.
Answer: A. They contain a paste-like electrolyte that reduces leakage problems
40. Which statement best explains why a dry cell is convenient for portable devices?
A. Its liquid electrolyte can flow easily.
B. Its paste electrolyte makes leakage less likely.
C. It does not use chemical reactions.
D. It has no positive terminal.
Answer: B. Its paste electrolyte makes leakage less likely