CBSE Class 8 Science Chapter 04 Electricity Magnetic And Heating Effects MCQs Set 02

Multiple Choice Questions (MCQs) for Class 8 Science: Chapter 04 Electricity Magnetic And Heating Effects

Explore reliable objective questions for Chapter 04 Electricity Magnetic And Heating Effects tailored for Class 8 learners. Utilizing these Science multiple-choice formats ensures thorough preparation and strengthens problem-solving speed for upcoming school assessments.

Practice Chapter 04 Electricity Magnetic And Heating Effects MCQs for Class 8 Science

Navigate directly to the 50 objective questions for Chapter 04 Electricity Magnetic And Heating Effects using the digital viewer below. Each practice set includes verified answer keys, allowing students to instantly cross-check their work and identify areas requiring further revision.

Question: When a compass needle is placed below a straight wire carrying electric current, the needle deflects. According to the chapter, what does this deflection specifically indicate?
A. The wire has become magnetic due to the flowing current
B. The compass needle is damaged and cannot function properly
C. The compass was not calibrated correctly before the experiment
D. Magnetic materials within the wire are being attracted outward
Show Answer & Explanation

Answer: (A) The wire has become magnetic due to the flowing current

Explanation:
The deflection of the compass needle shows that the current-carrying wire produces a magnetic field around it. This magnetic field exerts a force on the compass needle (which is itself a tiny magnet), causing it to move away from its normal north-south orientation. The chapter defines this region of magnetic influence as a magnetic field.

Question: In the exhibition, Sumana's lifting electromagnet fascinated Mohini and Aakarsh because the iron nail wrapped with wire could attract paper clips without being a permanent magnet. Which statement best explains how this temporary magnetic effect is achieved?
A. a) The iron nail itself generates electricity when wrapped with wire
B. b) Electric current flowing through the wire creates a magnetic field around it
C. c) The wire becomes hot and transfers thermal energy to the nail
D. d) The metal in the wire undergoes a permanent chemical change
Show Answer & Explanation

Answer: (B) b) Electric current flowing through the wire creates a magnetic field around it

Explanation:
When electric current flows through a conductor like the wire, it produces a magnetic field around it. This is the magnetic effect of electric current. The nail becomes magnetic only while current flows; once the circuit opens, the magnetic effect disappears and the clips fall off.

Question: During Activity 4.3, students wound insulated wire around a cylindrical coil and observed compass deflections at both ends. After inserting an iron nail through the centre, the compass deflections increased significantly. What is the reason for this increased deflection?
A. a) The iron nail conducts electricity better than the paper cylinder
B. b) The iron nail strengthens the magnetic field produced by the current-carrying coil
C. c) The temperature of the wire increases when iron is inserted
D. d) The iron nail reduces the resistance of the circuit, causing more current to flow
Show Answer & Explanation

Answer: (B) b) The iron nail strengthens the magnetic field produced by the current-carrying coil

Explanation:
• Iron core amplifies the magnetic field generated by the coil
• Most practical electromagnets use iron cores to make them stronger
• The increased compass deflection indicates a stronger magnetic effect, not more current or heat
• This principle is why electromagnets with iron cores can attract more clips than coils without cores.

Question: In Activity 4.5, students touched a nichrome wire at room temperature and felt nothing unusual. After passing current for 30 seconds and turning it off, the wire felt noticeably warm. Which sequence of energy transformations occurs in the nichrome wire?
A. a) Electrical energy → kinetic energy → thermal energy
B. b) Electrical energy → thermal energy (due to resistance) → dissipated as heat
C. c) Thermal energy → electrical energy → light energy
D. d) Mechanical energy → electrical energy → thermal energy
Show Answer & Explanation

Answer: (B) b) Electrical energy → thermal energy (due to resistance) → dissipated as heat

Explanation:
The nichrome wire offers resistance to the flow of electric current. This resistance converts electrical energy into heat energy, warming the wire. Different conductors offer different levels of resistance; nichrome offers higher resistance than copper, generating more heat for the same current.

Question: In the lemon cell experiment (Activity 4.6), when students connected five lemons in series with copper wires and iron nails as electrodes, an LED eventually glowed. Which role does the lemon juice specifically perform in this cell?
A. a) It provides the electrons that flow through the external circuit
B. b) It acts as an electrolyte, enabling ions to move between the electrodes
C. c) It generates heat that powers the LED
D. d) It prevents oxidation of the metal electrodes
Show Answer & Explanation

Answer: (B) b) It acts as an electrolyte, enabling ions to move between the electrodes

Explanation:
Lemon juice is a weak acid solution that serves as the electrolyte in a Voltaic cell. It allows ions to move internally between the two metal electrodes (copper and iron), which is essential for chemical reactions to generate electric current. Without this ionic movement, no current could flow.

Question: According to the chapter's 'Be a scientist' section about Hans Christian Oersted's discovery in 1820, why was his finding that electricity and magnetism are linked considered important?
A. a) It showed that electricity and magnetism were completely unrelated phenomena
B. b) It proved that magnetic fields could only be produced by permanent magnets
C. c) It revealed a fundamental connection between electricity and magnetism, leading to further scientific investigation
D. d) It demonstrated that electric current always causes heating
Show Answer & Explanation

Answer: (C) c) It revealed a fundamental connection between electricity and magnetism, leading to further scientific investigation

Explanation:
Oersted's observation that a compass needle deflected when an electrical circuit was opened or closed revealed an unexpected link between electricity and magnetism. This inspired other scientists to repeat and extend his work, deepening our understanding of electromagnetism and its applications.

Question: A student constructs two electromagnets: one using 50 turns of wire around an iron nail, and another using 100 turns of wire around an identical nail. Both are connected to the same cell. Which electromagnet will attract more iron paper clips, and why?
A. a) The 50-turn electromagnet, because fewer turns reduce heat loss
B. b) The 100-turn electromagnet, because the increase in number of turns strengthens the magnetic field
C. c) Both will attract the same number of clips, since the current and nail are identical
D. d) The 50-turn electromagnet, because it allows current to flow faster
Show Answer & Explanation

Answer: (B) b) The 100-turn electromagnet, because the increase in number of turns strengthens the magnetic field

Explanation:
The chapter's 'Think like a scientist' section explicitly states that increasing the number of turns of the coil makes the electromagnet stronger. More turns mean a stronger magnetic field is generated by the same current, allowing it to attract more iron clips.

Question: In households, overheating in electrical circuits can cause damage to plugs and sockets where plastic parts melt or even lead to fires. According to the chapter, what is the recommended safety measure to prevent such incidents?
A. a) Use thinner wires to reduce current flow
B. b) Keep electrical appliances turned off most of the time
C. c) Use appropriate wires, plugs, and sockets rated for the specified electric current
D. d) Avoid using heating appliances altogether
Show Answer & Explanation

Answer: (C) c) Use appropriate wires, plugs, and sockets rated for the specified electric current

Explanation:
The chapter's 'A step further' section specifically recommends using appropriate wires, plugs, and sockets that are rated for the specified electric current of the connections. This prevents excessive heat generation due to inappropriate resistance in the circuit.

Question: In the introduction story, when Sumana opened the circuit by moving the switch to OFF, the iron paper clips fell from the electromagnet's nail. This observation demonstrates which concept about electromagnets?
A. a) Electromagnets have permanent magnetic properties like bar magnets
B. b) The magnetic effect of an electromagnet depends on current flowing through it
C. c) Iron paper clips cannot be attracted by electromagnets
D. d) Once magnetized, an iron nail retains its magnetism indefinitely
Show Answer & Explanation

Answer: (B) b) The magnetic effect of an electromagnet depends on current flowing through it

Explanation:
The instant loss of magnetic effect when the switch opens shows that an electromagnet's magnetism is temporary and dependent on electric current. Unlike permanent magnets, electromagnets lose their magnetic properties immediately when current stops flowing.

Question: In Activity 4.4, a compass needle placed near end A of an electromagnet showed that the north pole of the compass was attracted to end A. What can be concluded about end A of the electromagnet?
A. a) End A is the north pole of the electromagnet
B. b) End A is the south pole of the electromagnet
C. c) End A has no magnetic polarity
D. d) End A attracts both north and south poles equally
Show Answer & Explanation

Answer: (B) b) End A is the south pole of the electromagnet

Explanation:
Since unlike poles attract, if the north pole of the compass is attracted to end A, then end A must be the south pole of the electromagnet. This principle—that opposite poles attract—is used to determine the polarity of electromagnets.

Question: The chapter compares dry cells with Voltaic cells. Which statement accurately reflects the key distinction between these two types of cells in terms of their practical use?
A. a) Voltaic cells are more portable because they use liquid electrolytes
B. b) Dry cells are more convenient for everyday use because the electrolyte is a thick paste
C. c) Both are equally convenient, but Voltaic cells last longer
D. d) Dry cells are unreliable and should never be used in circuits
Show Answer & Explanation

Answer: (B) b) Dry cells are more convenient for everyday use because the electrolyte is a thick paste

Explanation:
Unlike Voltaic cells with liquid electrolytes that can spill, dry cells have a thick moist paste as the electrolyte, making them safer and more suitable for portable devices. This convenience made dry cells widely adopted for everyday applications despite the fact that Voltaic cells were discovered earlier.

Question: Based on the Earth's magnetism discussion in the chapter's 'A step further' section, which statement correctly explains how Earth maintains its magnetic field?
A. a) Earth's magnetic field comes from permanent magnets buried deep underground
B. b) Movement of liquid iron in Earth's core creates electric currents that generate a magnetic field
C. c) Earth's rotation alone is responsible for producing a magnetic field
D. d) Earth's magnetic field is artificially maintained by human technology
Show Answer & Explanation

Answer: (B) b) Movement of liquid iron in Earth's core creates electric currents that generate a magnetic field

Explanation:
The chapter explicitly states that movement of liquid iron in Earth's core creates electric currents, which generate a magnetic field. This natural electromagnet-like phenomenon protects life on Earth and helps organisms like migratory birds navigate.

Question: In the 'Ever heard of...' section about steel manufacturing, high-temperature furnaces use electric current to generate heat for melting and recycling scrap steel. This application is based on which effect of electric current?
A. a) The magnetic effect of electric current
B. b) The mechanical effect of electric current
C. c) The heating effect of electric current
D. d) The chemical effect of electric current
Show Answer & Explanation

Answer: (C) c) The heating effect of electric current

Explanation:
The industrial furnace uses electric current to produce heat for melting steel. This is a direct application of the heating effect of electric current—when current flows through a conductor with resistance, electrical energy converts to heat energy. This industrial use demonstrates the practical importance of understanding resistance and heat generation.

Question: A student observes that when nichrome wire and copper wire of the same size and length carry the same current for 30 seconds, the nichrome wire becomes much hotter. What explains this difference in heating?
A. a) Copper conducts heat away faster than nichrome
B. b) Nichrome has higher electrical resistance than copper, generating more heat
C. c) The current through nichrome wire is actually stronger than through copper
D. d) Nichrome is thinner than copper, so it heats up faster
Show Answer & Explanation

Answer: (B) b) Nichrome has higher electrical resistance than copper, generating more heat

Explanation:
The chapter states that different conductors offer different levels of resistance. Nichrome offers higher resistance compared to copper wire of the same size and length. Since heat generation is related to resistance, nichrome produces more heat for the same current, which is why it's commonly used in heating appliances.

Question: Rechargeable batteries can be charged and discharged multiple times, yet the chapter notes they eventually 'slowly wear out' even after being recharged many times. What is implied about the lifespan of rechargeable batteries?
A. a) They can be recharged infinitely without any degradation
B. b) They retain full capacity throughout their entire lifespan
C. c) Although reusable, they have a finite lifespan and eventually become unable to hold charge
D. d) Once they start to wear out, they become completely unusable instantly
Show Answer & Explanation

Answer: (C) c) Although reusable, they have a finite lifespan and eventually become unable to hold charge

Explanation:
The chapter explains that rechargeable batteries can be recharged multiple times, preventing wastage and saving money. However, after repeated charging and use cycles, the internal chemical materials gradually degrade, causing the battery to wear out and eventually lose its ability to hold charge effectively. This is why older phone batteries need charging more frequently.

Question: If an electromagnet with a coil of wire wrapped around an iron nail is connected to a cell with the positive terminal at end A and negative terminal at end B, and then the battery terminals are reversed (positive at B, negative at A), what happens to the electromagnet?
A. a) The electromagnet becomes weaker because the current direction changes
B. b) The electromagnet retains the same polarity at both ends
C. c) The magnetic poles at the ends reverse their positions—end B becomes north and end A becomes south
D. d) The electromagnet stops working completely and cannot be restarted
Show Answer & Explanation

Answer: (C) c) The magnetic poles at the ends reverse their positions—end B becomes north and end A becomes south

Explanation:
The chapter's 'Think like a scientist' section states that the poles of an electromagnet can be reversed by changing the direction of the current. Reversing battery terminals reverses current direction, which reverses which end becomes the north pole and which becomes the south pole.

Question: In the scenario at the end of the chapter (question 8), Sumana forgets to turn off her electromagnet. After some time, the electromagnet stops picking up clips, but the wire is still warm. Which statement best explains this observation?
A. a) The electrical cell has become completely dead and no longer provides current
B. b) The iron nail has become permanently magnetized and no longer responds to the coil
C. c) The cell may have weakened, reducing the current strength below what is needed to attract clips, though residual current still heats the wire
D. d) The wire has melted and can no longer carry current to the electromagnet
Show Answer & Explanation

Answer: (C) c) The cell may have weakened, reducing the current strength below what is needed to attract clips, though residual current still heats the wire

Explanation:
If the wire is still warm, current is still flowing through it (causing the heating effect). However, if the electromagnet cannot pick up clips, the current may be too weak to generate a sufficient magnetic field. This could happen if the cell weakened over time, leaving just enough current for heating but not enough for magnetism. Alternatively, the electromagnet's core may have demagnetized due to prolonged heating or fatigue.

Question: In Activity 4.1, when students closed the switch to allow electric current to flow through the wire stretched between two nails, they observed that a magnetic compass placed beneath the wire showed deflection. What does this deflection reveal about the relationship between electricity and magnetism?
A. Electric current repels magnetic needles in all directions equally
B. A flowing electric current creates a magnetic field around the conductor
C. Magnetic fields can only be created by permanent magnets made of iron
D. The compass needle deflects randomly without any connection to the current
Show Answer & Explanation

Answer: (B) A flowing electric current creates a magnetic field around the conductor

Explanation:
The chapter explicitly states that the deflection of the compass needle indicates a magnetic field exists around the current-carrying wire. This observation demonstrated that when electric current flows through a conductor, it produces a magnetic field—the foundational concept of the magnetic effect of electric current that Oersted discovered in 1820.

Question: When Sumana's electromagnet in the science exhibition picked up iron paper clips as long as current flowed, but the clips fell off when she opened the circuit, what property of electromagnets does this behaviour demonstrate?
A. Electromagnets are stronger than all permanent magnets
B. The magnetic effect of an electromagnet depends on continuous current flow
C. Iron nails become permanently magnetized after being used in electromagnets
D. Electromagnets can only attract non-ferrous metals like copper
Show Answer & Explanation

Answer: (B) The magnetic effect of an electromagnet depends on continuous current flow

Explanation:
This directly illustrates that electromagnets lose their magnetic effect when current stops flowing. Unlike permanent magnets, their magnetic properties are temporary and depend entirely on the presence of electric current through the coil.

Question: When students tested a nichrome wire by passing current through it for 30 seconds in Activity 4.5, the wire became noticeably warm. Which of the following best explains why this heating occurs?
A. The wire expands when current flows, creating friction that generates heat
B. Nichrome wire vibrates at high frequencies when carrying electric current
C. Current encounters resistance in the wire, converting electrical energy into heat energy
D. The magnetic field created around the wire causes its atoms to move faster
Show Answer & Explanation

Answer: (C) Current encounters resistance in the wire, converting electrical energy into heat energy

Explanation:
The chapter explains that when electric current flows through any conductor, it faces opposition or resistance. This resistance causes some electrical energy to be converted into heat energy—the heating effect of electric current. Nichrome wire specifically offers higher resistance than copper wire of the same size, which is why it heats up more.

Question: In the 'Ever heard of...' section about Alessandro Volta and Luigi Galvani, Volta disagreed with Galvani's interpretation of their frog-leg experiment. How did Volta test his different hypothesis about where the electricity originated?
A. He repeated the experiment with different frog species to see if results varied
B. He used saltwater-soaked paper instead of a frog's leg and still obtained electric current
C. He inserted copper and iron wires directly into the frog's muscle tissue
D. He measured the electrical current using an instrument that Galvani had invented
Show Answer & Explanation

Answer: (B) He used saltwater-soaked paper instead of a frog's leg and still obtained electric current

Explanation:
The chapter states that Volta used saltwater-soaked paper instead of a frog's leg and still got electric current, proving the electricity came from the metals and liquid combination, not the frog itself. This ingenious modification led to the invention of the first battery.

Question: In Activity 4.6, students connected five lemons in series with copper wires and iron nails, and an LED eventually glowed. If a student had used pure distilled water instead of lemon juice and kept everything else identical, what would most likely happen?
A. The LED would glow much brighter because pure water is a better conductor
B. The LED would not glow because pure water does not conduct electricity well
C. The number of lemons needed would double to achieve the same brightness
D. The copper wire would corrode faster and weaken the electrical connection
Show Answer & Explanation

Answer: (B) The LED would not glow because pure water does not conduct electricity well

Explanation:
Lemon juice contains dissolved salts and acids that make it a conductor of electricity. Pure distilled water lacks these ions and does not conduct electricity effectively, so no current would flow through the circuit and the LED would remain dark. The electrolyte's role is critical to generating electric current in a Voltaic cell.

Question: A dry cell differs from a Voltaic cell primarily in the nature of its electrolyte. Based on the chapter's description, what is the practical advantage of a dry cell over a Voltaic cell?
A. A dry cell generates much stronger electric current than a Voltaic cell
B. A dry cell's paste-like electrolyte prevents the liquid from spilling, making it portable for everyday use
C. A dry cell can be recharged multiple times while Voltaic cells cannot
D. A dry cell works only in outdoor environments while Voltaic cells work indoors
Show Answer & Explanation

Answer: (B) A dry cell's paste-like electrolyte prevents the liquid from spilling, making it portable for everyday use

Explanation:
The chapter explains that dry cells have a thick moist paste as electrolyte instead of liquid, making them much more convenient and portable for everyday applications compared to Voltaic cells, which contained liquid electrolyte in open containers.

Question: When an iron nail is inserted into the cylindrical coil in Activity 4.3, the magnetic compass needles show much greater deflection compared to when no nail is present. Which statement best explains why the iron nail causes this significant increase in the compass deflection?
A. The iron nail reduces the resistance of the wire, allowing more current to flow
B. The iron nail becomes magnetized by the current and amplifies the magnetic field produced by the coil
C. The iron nail attracts the compass needle directly, making deflection more visible
D. The iron nail conducts electricity better than the wire, creating a stronger field
Show Answer & Explanation

Answer: (B) The iron nail becomes magnetized by the current and amplifies the magnetic field produced by the coil

Explanation:
The iron nail becomes magnetized when current flows through the surrounding coil and amplifies the magnetic field that would otherwise be produced by the coil alone. The chapter explicitly states that when an iron nail is inserted in the core of the coil, 'the coil becomes a stronger magnet' and the magnetic compass needle deflection is 'much more.' This amplification is the defining characteristic of using an iron core in electromagnets for practical applications.

Question: In the lemon cell experiment (Activity 4.6), if a student constructed a working cell with copper wires and iron nails inserted in lemon juice, but then accidentally used pure water instead of lemon juice while keeping all other materials identical, what would most likely occur?
A. The LED would glow as brightly as before because pure water also conducts electricity
B. The LED would not glow because pure water does not conduct electricity well enough to allow current to flow
C. The LED would glow dimly at first but then become brighter as the pure water slowly becomes acidic
D. The LED would glow only if the student used thicker copper wires to compensate for water's resistance
Show Answer & Explanation

Answer: (B) The LED would not glow because pure water does not conduct electricity well enough to allow current to flow

Explanation:
Pure water is a poor conductor of electricity, while lemon juice contains acids and ions that enable electrical conductivity. The electrolyte in a Voltaic cell must conduct ions between the electrodes to complete the circuit. Without an effective electrolyte like lemon juice or a salt solution, the cell cannot generate sufficient current for the LED to glow, even though the metal electrodes and basic structure remain the same.

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Multiple Choice Questions (MCQs) for Class 8 Science Chapter 04 Electricity Magnetic And Heating Effects

Class 8 Science Chapter 04 Electricity Magnetic And Heating Effects Objective Test Questions

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