Provided here are the most accurate and elaborate RBSE Class 8 Science Chapter 11 Effects of Electric Current solutions for your reference. We are also offering numerous additional questions and their solutions, which are important for your preparation of the examination.
These RBSE solutions for Class 8 are accurate, elaborate and structured according to the standards set by the board. With all these questions and solutions, you will be able to excel in your exams with flying colours.
Rajasthan Board Class 8 Science Chapter 11: BYJU’S Important Questions & Answers
RBSE Class 8 Science Chapter 11 Objective Questions: Textbook Important Questions and Solutions
Q1. Electric bell is based on which electric current effect?
(A) Thermal effect
(B) Magnetic effect
(C) Chemical effects
(D) Joule effect
Answer: (B) Magnetic effect
Q2. What is the object used to collect the magnetic matter from this scrape?
(A) Electric magnet
(B) Electric cell
(C) Fuse
(D) Immersion rod
Answer: (A) Electric magnet
Q3. Which of the following solutions do not pass electric current?
(A) Copper sulphate
(B) Silver nitrate
(C) Pure water
(D) Salted water
Answer: (D) Salted Water
Q4. Which is not a component of an electric bell?
(A) Strip of iron
(B) Coil
(C) Contact nut
(D) Magnetic needle
Answer: (D) Magnetic needle
RBSE Class 8 Science Chapter 11 Fill in the blanks: Textbook Important Questions and Solutions
Q1. The long line represents ___________ and the short line represents ___________ terminal of the electric battery’s symbol.
Answer: Positive terminal, negative terminal
Q2. The safety device based on the heating effect of electric current is called ___________.
Answer: Fuse
Q3. In a battery, the plate connected to the positive terminal is called ___________ and to the negative terminal is called ___________.
Answer: Anode, cathode
Q4. The magnetic effect of electric current is discovered by ___________.
Answer: Hans Christian Oersted
RBSE Class 8 Science Chapter 11 Short Answer Type Questions: Textbook Important Questions and Solutions
Q1. What is a fuse?
Answer: Fuse is a safety device that protects the damage to electrical appliances. It melts when the electric current exceeds the safety limit making the current flow stop in the circuit and thereby, protecting the electrical appliance.
Q2. Write any three applications of an electromagnet.
Answer: Three applications of an electromagnet are as follows:
1. To collect magnetic materials from a scrape.
2. Electromagnetic crane is utilized to lift heavy iron objects.
3. It is used by doctors to draw pieces of iron or magnetic material, which has fallen into the eye of a person.
Q3. What is the thermal effect of electric current? Write down the names of any four appliances based on this effect.
Answer: Conductors become hot when an electric current passes through them. This is the heating effect or the thermal effect of electric current.
Appliances that work based on this effect are:
– Electric oven
– Electric toaster
– Immersion rod
– Electric bulb
RBSE Class 8 Science Chapter 11 Long Answer Type Questions: Textbook Important Questions and Solutions
Q4. Make a diagram of an electric bell and explain its working system.
Answer:
An electric bell has the following elements:
– Coil
– Iron Strip
– Contact Screw
– Hammer
– Bell
The coil is wrapped with many insulated copper wires on the iron core. A strip of iron attached with a hammer at one end is attached to the nearby coil. There is a contact screw near the iron strip.
When the electric switch is switched on, an electric current flows through the coil. Due to the magnetic effect of the electric current, an electromagnet is formed. Then it attracts the electromagnet. The hammer at the end of the strip strikes the gong of the bell to produce a sound. When the electromagnet attracts the iron strips, then the screw does not remain in contact with it and the circuit breaks. The current through the coil stops flowing.
The iron strip gets back to its original position and thus the circuit is completed. The electric current passes through the coil and the gong is struck by the hammer again.
Q5. What is the chemical effect of electric current? Explain the process of electroplating.
Answer: Chemical effect of Electric Current:
When an electric current is allowed to pass through a conducting solution, it forms an effect on that solution.
As a result of this, bubbles of gas may get formed at the electrodes. The colour of the solution too might change. We might see deposits of metals on the electrodes. The changes depend on the solution and electrodes being used. These are some of the chemical effects of electric current.
Electroplating is the process in which the desired metal is deposited on any material due to the chemical effect of electric current. It has wide applications in industry. For instance, to deposit a gold/silver layer on ornaments, chromium plating on some portions of cars, to deposit a layer of zinc on iron to protect it from corrosion, etc.
RBSE Class 8 Science Chapter 11 Additional Important Questions and Solutions
Q6. Explain the relation between the heat produced in the wire with the wire resistance. Also, what are the other factors that affect heat production in a wire?
Answer: The higher the resistance offered by the wire to the current flow, the more will be the heat produced. That is why nichrome and tungsten wires get heated up as they offer high resistance to the flow of current. But, the copper wires do not get heated up as they offer a very little amount of resistance to the flow of current.
Apart from the material used, the amount of heat produced in a wire also relies on the length of the wire as well as its thickness.
Q7. Explain the heating effect of electric current with an activity.
Answer: Take a thin nichrome wire and wrap it around a pencil. Connect one end of the nichrome wire to a cell and the other end with a key.
After plugging in the key, electric current flows through the circuit. We will see that the nichrome wire gets heated up.
If we switch off the key and wait for some time, the nichrome wire will cool down. Thus, we can say that the wire gets heated up when an electric current flows through it. This is called the heating effect of electric current.
Q8. Define phase.
Answer: Three types of wires are used in our homes to supply electricity.
The sockets used have three holes in them. The socket’s end in which the tester is inserted and it lights up is called the electric live wire or the phase.
Usually, a red coloured plastic is wrapped around this wire.
Q9. Define neutral wire.
Answer: The socket’s end near the phase socket in which when the tester is inserted, it does not produce light, is called the neutral wire. The neutral wire is set at zero voltage. Normally, the neutral wire is coated with black-coloured plastic. 220V current is supplied between the two wires: live wire and the neutral wire.
Q10. What are the factors on which the amount of heat produced in a wire depends?
Answer: The amount of heat produced in a wire depends on:
1. The resistance offered by the material used to build the wire
2. The length of the wire
3. The thickness of the wire
Q11. What do we mean by a short circuit?
Answer: When the phase wire and the neutral wire come in contact with each other due to any reason, then a short circuit occurs. During a short circuit, a huge amount of electricity flows through the circuit. Due to overheating, the appliances might catch fire or might even burn. The excess connections into the socket may result in high electric current flow in the circuit. Thus, we should not plug in more devices into a single socket.
12. What are the causes of the short circuit?
Answer: In case the insulation of the wires used in the circuit is destroyed or if the electric device used is faulty, the live wire and the neutral wire can come in direct contact with each other. As a result, current in the circuit rises and the short circuit occurs.
The short circuit can happen because of the wear and tear of old wires.
If the electric current flowing through the circuit is excessive, the wires might melt due to the heat.
Q13. What are the losses due to a short circuit?
Answer: During a short circuit excessive electric current flows through circuits. Due to this, electric appliances might get heated up and catch fire. This, as a result, may even cause a fire accident.
Q14. Define earthing.
Answer: In the socket, the third hole is for the earthing wire. This wire has a green coloured plastic wrapped around it. Earthing wire is connected to the copper plate underground. It is a safety measure to prevent a person from undergoing an electric shock in case the phase wire comes in contact with the metallic body of an appliance.
Q15. What are the effects of electric current?
Answer: The effects of electric current are as follows:
(i) chemical effect of electric current
(ii) heating effect of electric current
(iii) magnetic effect of electric current
Q16. What are the main components of the electric circuit?
Answer: Every electric circuit has three basic components:
(a) Energy source
For instance, an electric cell, a generator, a battery
(b) an output device
For instance, an electric bulb, motor, electric device, lamp etc. to draw current
(c) a conducting device
For instance, a conducting wire, cable, etc.
Q17. In which direction does the electric current flow? Which liquids work as electric conductors?
Answer: The electric current flows where the positive charge moves. The electrons move in the opposite direction through the conducting wire. The current flows from the positive terminal of the battery to the negative terminal of the battery.
The liquids that work as electric conductors are acid solutions, salt solutions and basic solutions.
Q18. What is a fuse made up of? Explain in detail.
Answer: The ends of the fuse wire are kept in porcelain or such other insulator cartridge. The wire is normally made up of mixed metals such as copper, zinc and tin. These metals have a lower melting point than the melting points of metals used in other wires that are used in electrical appliances and circuits.
Q19. What is an MCB?
Answer: MCBs are Miniature circuit breakers. They are used as a substitute for a fuse. They have switches that automatically switch off when the flow of current exceeds a certain limit.
As and when we switch them on, the circuit gets completed and electrical appliances begin to work as usual.
Q20. Define electrolysis and electroplating.
Answer: Electrolysis: Electrolysis is defined as a process of decomposing ionic compounds into their elements by passing a direct electric current through the compound in a fluid form. The cations are reduced at cathode and anions are oxidized at the anode.
Electroplating: Electroplating is the process in which the desired metal is deposited on any material due to the chemical effect of electric current. It has wide applications in industry. For instance, to deposit a gold/silver layer on ornaments, chromium plating on some portions of cars, to deposit a layer of zinc on iron to protect it from corrosion, etc.
Q21. What are conductors of electricity? Give examples.
Answer: In simple terms, an electrical conductor is defined as materials that allow electricity to flow through them easily. This property of conductors that allow them to conduct electricity is known as conductivity.
Some of the common conductor examples include metals such as:
– Copper
– Gold
– Iron
Q22. What are insulators of electricity? Give examples.
Answer: Insulators are materials that hinder the free flow of electrons from one particle of the element to another. If we transfer some amount of charge to such an element at any point, the charge remains at the initial location and does not get distributed across the surface. The common process of charging of such elements includes charging by rubbing (for some elements, with the help of suitable materials) and charging by induction.
Some of the common insulator examples are given below:
– Plastic
– Wood
– Glass
Q23. What are the differences between conductors and insulators?
Answer: The differences between conductors and insulators are as follows:
|
Conductors |
Insulators |
|
Materials that permit electricity or heat to pass through it |
Materials that do not permit heat and electricity to pass through it |
|
A few examples of a conductor are silver, aluminium and iron |
A few examples of an insulator are paper, wood and rubber |
|
The electrons move freely within the conductor |
The electrons do not move freely within the insulator |
|
The electric field exists on the surface but remains zero on the inside |
The electric field doesn’t exist |
Q24. Why is it so that ordinary water conducts electricity but distilled water does not?
Answer: Normal or ordinary water is said to have impurities present in the form of ions called minerals etc. These ions are known to be responsible for the conduction of electric current in the water. The electrical current in water is transported by the ions present in them, and the conductivity is said to increase with the increase in the concentration of ions in them.
Distilled water is free of salt. That’s why it does not conduct electricity.
Q25. What is a tester?
Answer: A tester is an electrical instrument that is used to examine the flow of electric current. The tester is brought in contact with the terminals of the electric circuit.
The tester has a bulb. If this bulb glows when the tester is brought in contact with the terminals, it implies that an electric current is flowing through the circuit.
Q26. How does an electric bulb glow when the electric current passes through it?
Answer: When an electric current is passed through an electric bulb, it makes the bulb get hot as a result of the heating effect of electric current. The bulb starts to glow. If the intensity of the current is too low, then the bulb does not get enough heat and thus, does not glow.
Q27. What do we mean by electrolysis?
Answer: Electrolysis is defined as a process of decomposing ionic compounds into their elements by passing a direct electric current through the compound in a fluid form. The cations are reduced at cathode and anions are oxidized at the anode.
Q28. How was the magnetic effect of electric current discovered?
Answer: The magnetic needle deflects when it is brought near a wire in which electric current is passing through. By these observations, Oersted discovered the magnetic effect of electric current.
Q29. Describe the chemical effect of electric current.
Answer: When an electric current is allowed to pass through a conducting solution, it forms an effect on that solution. As a result of this, bubbles of gas may get formed at the electrodes. The colour of the solution too might change. We might see deposits of metals on the electrodes. The changes depend on the solution and electrodes being used. These are some of the chemical effects of electric current.
Q30. Explain the concept of a short circuit in detail along with the factors responsible for a short circuit.
Answer: When the phase wire and the neutral wire come in contact with each other due to any reason, then a short circuit occurs. During a short circuit, a huge amount of electricity flows through the circuit. Due to overheating, the appliances might catch fire or might even burn. The excess connections into the socket may result in high electric current flow in the circuit. Thus, we should not plug in more devices into a single socket.
The causes of a short circuit are:
If the insulation of the wires used in the circuit is damaged or the appliance used is faulty due to which the live wire and the neutral wire comes in direct contact as a result current in the circuit rises and the short circuit occurs.
The short circuit can happen because of the wear and tear of old wires.
If the electric current flowing through the circuit is excessive, the wires might melt due to the heat.
Q31. What is the difference between a permanent magnet and an electromagnet?
Answer: Electromagnets are the magnets that function based on electricity.
In contrast to a permanent magnet, an electromagnet’s strength can be altered by making changes to the amount of electric current that passes through it. The electromagnetism of the electromagnet stops to exist when the current flow is stopped.
Q32. Define magnetic effect of electric current. Give examples of the same.
Answer: The magnetic needle deflects when it is brought near a wire in which electric current is passing through. By these observations, Oersted discovered the magnetic effect of electric current.
When electric current passes through a wire, it acts like a magnet. This is the magnetic effect of electric current.
Examples include:
– electric crane
– electric bell
– telephone
– telegraph
Q33. What is an electromagnet?
Answer: Electromagnets are prepared from a coil of wire, which means a wire coiled in series. The coiled wire is more effective in generating a magnetic field than a wire that is running straight. The effect of coiled wire can be made stronger by winding a wire firmly around a powerful core that is built of a magnetic item, such as iron.
The picture above shows a wire wound around an iron nail. On its own, the iron nail is not magnetic.
Q34. What are the uses and applications of an electromagnet?
Answer: Some electromagnet uses are given below:
– Particle Accelerators
– Amplifiers
– Magnetic Separation
– Electric Motors and Generators
– MRI machines
– Control Switches in Relays
– Transportation
– Spacecraft Propulsion Systems
– Induction Heating
– Hard Drives
Q35. What are the disadvantages of electromagnet?
Answer: A few disadvantages of electromagnetism are as follows:
– They heat up very fast
– It consumes a lot of energy
– They can store huge amounts of energy in their magnetic field. If the electric current is interrupted, the energy will discharge
Q36. What happens when electricity is passed through water?
Answer: When an electric current is passed through water, electrolysis of water happens. Water i.e. H2O is decomposed into the gases – Hydrogen and Oxygen i.e H2 and O2.
At the cathode, hydrogen gas is formed.
At the anode, oxygen is formed.
Q37. Fuse protects the circuit from overload. Explain.
Answer: Fuse is a safety device that protects the damage to electrical appliances. It melts when the electric current exceeds the safety limit making the current flow stop in the circuit and thereby, protecting the electrical appliance.
The ends of the fuse wire are kept in porcelain or such other insulator cartridge. And, the wire is normally made up of mixed metals such as copper, zinc and tin. These metals have a lower melting point than the melting points of metals used in other wires that are used in electrical appliances and circuits.
When there is an excessive flow of current in the circuit, then fuse wire gets heated up. Due to this heat, the fuse wire melts and this breaks the electrical circuit. Usually, the ends of the fuse wire are kept in porcelain or such other insulator cartridges. And, the wire is normally made up of mixed metals such as copper, zinc and tin. These metals have a lower melting point than the melting points of metals used in other wires that are used in electrical appliances and circuits.
Q38. Give examples of devices that work on the magnetic effect of electric current.
Answer: Examples of devices that operate on the magnetic effect of electric current include:
– Electric crane
– Electric bell
– Telephone
– Telegraph
Q39. Explain the working of a fuse in detail.
Answer: Fuse is a safety device that protects the damage to electrical appliances. It melts when the electric current exceeds the safety limit making the current flow stop in the circuit and thereby, protecting the electrical appliance.
When there is an excessive flow of current in the circuit, then fuse wire gets heated up. Due to this heat, the fuse wire melts and this breaks the electrical circuit. Usually, the ends of the fuse wire are kept in porcelain or such other insulator cartridges. The wire is normally made up of mixed metals such as copper, zinc and tin. These metals have a lower melting point than the melting points of metals used in other wires that are used in electrical appliances and circuits.
Q40. What are the wires used in our homes? Explain them all in detail.
Answer: Three types of wires are used in our homes to supply electricity: electric live wire, the neutral wire and earthing.
Phase or electric live wire:
The sockets used have three holes in them. The socket’s end in which the tester is inserted and it lights up is called the electric live wire or the phase.
Usually, a red coloured plastic is wrapped around this wire.
Neutral wire:
The socket’s end near the phase socket in which when the tester is inserted, it does not produce light, is called the neutral wire. The neutral wire is set at zero voltage. Normally, the neutral wire is coated with black-coloured plastic. 220V current is supplied between the two wires: live wire and the neutral wire.
Earthing wire:
In the socket, the third hole is for the earthing wire. This wire has a green coloured plastic wrapped around it. Earthing wire is connected to the copper plate underground. It is a safety measure to prevent a person from undergoing an electric shock in case the phase wire comes in contact with the metallic body of an appliance.
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