CBSE Class 8 Science Chapter 04 Electricity Magnetic And Heating Effects MCQs Set 01

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

Review structured MCQ sets for Class 8 Science Chapter 04 Electricity Magnetic And Heating Effects. Built according to official CBSE guidelines, these downloadable questions support daily revision and core concept reinforcement.

Access Chapter 04 Electricity Magnetic And Heating Effects Questions and Solutions

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 electric current flows through a conductor, it produces a magnetic field around it. This phenomenon was first discovered by which scientist in 1820?
A. Luigi Galvani
B. Hans Christian Oersted
C. Alessandro Volta
D. Michael Faraday
Show Answer & Explanation

Answer: (B) Hans Christian Oersted

Explanation:
The chapter explicitly states that Hans Christian Oersted, a professor at a university in Denmark, made this discovery in 1820 when he noticed that a compass needle deflected whenever an electrical circuit was closed or opened.

Question: In Activity 4.3, when the electromagnet was connected to the cell, the compass needles placed near the coil showed deflection. What additional change made the magnetic effect much stronger?
A. Increasing the length of the wire
B. Inserting an iron nail in the core of the coil
C. Using thicker connecting wires
D. Adding more cells to the battery
Show Answer & Explanation

Answer: (B) Inserting an iron nail in the core of the coil

Explanation:
The chapter describes that when an iron nail was inserted in the core of the coil, the deflection of the compass needle became much more pronounced, and the coil was able to attract iron clips. An iron core makes electromagnets stronger for practical applications.

Question: What is the primary reason why nichrome wire becomes warm when electric current passes through it?
A. The wire is made of a material that naturally generates heat
B. The current faces resistance as it flows through the wire, converting electrical energy to heat energy
C. The magnetic field around the wire causes friction
D. The wire loses its structural integrity under current flow
Show Answer & Explanation

Answer: (B) The current faces resistance as it flows through the wire, converting electrical energy to heat energy

Explanation:
The chapter explains that different conductors offer different levels of resistance to current flow. Nichrome wire offers higher resistance compared to copper wire of the same size and length, causing electrical energy to be converted into heat energy—this is the heating effect of electric current.

Question: In the lemon cell experiment (Activity 4.6), which components serve as the electrolyte?
A. The copper wire and iron nail
B. The lemon juice
C. The LED and connecting wires
D. The metal cap and carbon rod
Show Answer & Explanation

Answer: (B) The lemon juice

Explanation:
In Activity 4.6, the lemon juice acts as the electrolyte that helps conduct electricity between the copper wire (positive electrode) and iron nail (negative electrode), similar to how an electrolyte works in a Voltaic cell.

Question: Why are lifting electromagnets widely used in factories and scrap yards instead of permanent magnets?
A. They are cheaper to manufacture than permanent magnets
B. They can be turned on and off by controlling the electric current, allowing controlled lifting and releasing of metal objects
C. They produce a stronger magnetic field than any permanent magnet
D. They do not require any power source to operate
Show Answer & Explanation

Answer: (B) They can be turned on and off by controlling the electric current, allowing controlled lifting and releasing of metal objects

Explanation:
The chapter states that lifting electromagnets are strong electromagnets hung to cranes, and the operator can control the magnet by switching the current ON and OFF. When current is ON, the electromagnet lifts objects; when OFF, the magnetic field disappears and objects are released.

Question: According to the 'Think like a scientist' section, if you repeat Activity 4.3 with 2 cells instead of 1 cell using the same coil, what change would you observe?
A. The compass needle deflection would decrease
B. The compass needle deflection would remain the same
C. The compass needle deflection would increase and the coil would attract more clips
D. The wire would become warm but the magnetic effect would disappear
Show Answer & Explanation

Answer: (C) The compass needle deflection would increase and the coil would attract more clips

Explanation:
• A battery with more cells provides larger current than a single cell
• Larger current creates a stronger magnetic field
• Stronger magnetic field causes more deflection of compass needle and attracts more iron clips

Question: Which of the following is NOT a practical application of the heating effect of electric current mentioned in the chapter?
A. Electric room heaters
B. Electric irons
C. Water heating immersion rods
D. Electromagnets used in electric bells
Show Answer & Explanation

Answer: (D) Electromagnets used in electric bells

Explanation:
The chapter lists electric room heaters, stoves, kettles, irons, water heating immersion rods, and hair dryers as household appliances that work on the heating effect principle. Electromagnets in electric bells work on the magnetic effect of electric current, not the heating effect.

Question: What is a key difference between a Voltaic cell and a dry cell in terms of the electrolyte used?
A. Voltaic cells use electricity while dry cells use chemicals
B. Voltaic cells contain a liquid electrolyte while dry cells contain a thick moist paste
C. Dry cells cannot produce electricity while Voltaic cells can
D. Voltaic cells are rechargeable while dry cells are not
Show Answer & Explanation

Answer: (B) Voltaic cells contain a liquid electrolyte while dry cells contain a thick moist paste

Explanation:
The chapter describes that a Voltaic cell uses a liquid electrolyte (usually a weak acid or salt solution), whereas a dry cell uses a thick moist paste as the electrolyte, despite both operating on similar chemical principles.

Question: If you reverse the direction of current in an electromagnet, what happens to its poles?
A. The poles become weaker
B. The poles remain in the same position
C. The poles reverse or swap their positions
D. One pole disappears completely
Show Answer & Explanation

Answer: (C) The poles reverse or swap their positions

Explanation:
The chapter explicitly states in the 'Think like a scientist' section that an electromagnet's poles can be reversed by changing the direction of the current flowing through the coil.

Question: In the scenario described at the end of the chapter, when Sumana's electromagnet stopped picking up clips but the wire remained warm, what can be inferred?
A. The battery had completely died and no current was flowing
B. The cell was still providing current but the magnetic field was somehow disrupted
C. The heating effect continued while the magnetic effect was lost, suggesting possible chemical depletion or wire damage
D. The iron nail had become permanently magnetized and no longer needed current
Show Answer & Explanation

Answer: (C) The heating effect continued while the magnetic effect was lost, suggesting possible chemical depletion or wire damage

Explanation:
The question asks students to consider why the wire is warm (heating effect still present) but clips are not being lifted (magnetic effect lost). This suggests the cell is still supplying current (causing heat through resistance) but something prevents the electromagnet from functioning—possibly depleted chemicals affecting magnetism while not completely stopping current flow, or damage to the coil affecting its magnetic properties.

Question: What makes rechargeable batteries different from dry cells in terms of their lifespan and usage?
A. Rechargeable batteries can only be used once like dry cells
B. Rechargeable batteries can be recharged and reused multiple times, though they eventually wear out after many charge-discharge cycles
C. Rechargeable batteries never lose their effectiveness
D. Dry cells are more environmentally friendly because they cannot be recharged
Show Answer & Explanation

Answer: (B) Rechargeable batteries can be recharged and reused multiple times, though they eventually wear out after many charge-discharge cycles

Explanation:
The chapter explains that rechargeable batteries can be recharged and reused multiple times, preventing wastage and saving money, but they do not last forever and slowly wear out after being charged and used many times.

Question: Based on the Earth's magnetism discussion in 'A step further,' what creates Earth's magnetic field?
A. Permanent magnets buried deep inside Earth's crust
B. The movement of liquid iron in Earth's core, which creates electric currents and generates a magnetic field
C. The rotation of Earth around the Sun
D. Solar wind interacting with Earth's atmosphere
Show Answer & Explanation

Answer: (B) The movement of liquid iron in Earth's core, which creates electric currents and generates a magnetic field

Explanation:
The chapter states that deep inside the Earth, the movement of liquid iron in the core creates electric currents, which generate a magnetic field. This demonstrates how the magnetic effect of electric current applies even on a planetary scale.

Question: Why might the deflection of a compass needle be less pronounced when using a single copper wire compared to a coil of the same wire?
A. Copper does not conduct electricity well enough
B. A coil concentrates the magnetic field effect over multiple turns, creating a stronger cumulative magnetic effect than a single straight wire
C. Compass needles are repelled by coils but attracted to straight wires
D. Single wires generate heat while coils do not
Show Answer & Explanation

Answer: (B) A coil concentrates the magnetic field effect over multiple turns, creating a stronger cumulative magnetic effect than a single straight wire

Explanation:
When wire is wrapped into a coil with multiple turns, the magnetic fields from each turn add together, creating a much stronger overall magnetic field. A single straight wire produces a weaker magnetic field that would deflect the compass needle less noticeably.

Question: In Activity 4.4, to determine whether end A of an electromagnet is a north or south pole, students observe which pole of the compass is attracted to it. Why does this method work?
A. The compass needle has no magnetic poles and simply responds to electrical signals
B. Unlike poles of magnets attract each other, so if the compass's north pole is attracted to end A, then end A must be a south pole
C. All electromagnet poles are the same regardless of which pole the compass points toward
D. The compass pole that points away indicates the electromagnet's pole type
Show Answer & Explanation

Answer: (B) Unlike poles of magnets attract each other, so if the compass's north pole is attracted to end A, then end A must be a south pole

Explanation:
The chapter explains that when two magnets are brought close, their unlike poles attract. Therefore, if the north pole of the compass needle is attracted toward end A of the electromagnet, end A must be a south pole—this is a direct application of magnet pole behavior.

Question: Which statement best explains why using appropriate wires, plugs, and sockets rated for specified electric current is important in households?
A. It makes the appliances work faster and more efficiently
B. It prevents unnecessary overheating in switchboards, reducing fire risk and damage to connections
C. It ensures the current flows in only one direction through the circuit
D. It increases the lifespan of batteries used in the home
Show Answer & Explanation

Answer: (B) It prevents unnecessary overheating in switchboards, reducing fire risk and damage to connections

Explanation:
The chapter warns that the heating effect of current can cause problems including energy loss in wires and overheating in appliances, which may damage plugs and sockets or lead to fires. Using appropriately rated components prevents excessive heating by ensuring they are designed to handle the specified current safely.

Question: When a current-carrying wire is placed near a magnetic compass, the compass needle deflects. According to the chapter, what causes this deflection?
A. The wire becomes magnetized permanently due to the current.
B. The flowing electric current produces a magnetic field around the wire.
C. The heat generated in the wire attracts the compass needle.
D. The wire and compass interact through their chemical properties.
Show Answer & Explanation

Answer: (B) The flowing electric current produces a magnetic field around the wire.

Explanation:
The chapter explains that when electric current flows through a conductor, it produces a magnetic field around it, and this magnetic field is what deflects the compass needle. This was discovered by Hans Christian Oersted in 1820.

Question: In the electromagnet experiments, why does inserting an iron nail into the coil make the electromagnet significantly stronger?
A. The nail conducts electricity better than the coil wire.
B. The nail amplifies the magnetic field produced by the current-carrying coil.
C. Iron nails generate heat that strengthens the magnetic effect.
D. The nail prevents the current from flowing through the coil.
Show Answer & Explanation

Answer: (B) The nail amplifies the magnetic field produced by the current-carrying coil.

Explanation:
• The iron core concentrates and amplifies the magnetic field
• The chapter states that for practical electromagnets, an iron core is used to make them stronger
• Without the core, the magnetic field is weaker and attracts fewer iron clips

Question: In Activity 4.5 with the nichrome wire, when the switch is moved to ON position for 30 seconds and then back to OFF, students observe the wire becomes warm. Which of the following best explains this observation?
A. Nichrome wire is made of materials that generate heat spontaneously.
B. The resistance in the nichrome wire causes some electrical energy to convert to heat energy.
C. The magnetic field created by the current heats the wire.
D. Friction between the wire and air causes the heating.
Show Answer & Explanation

Answer: (B) The resistance in the nichrome wire causes some electrical energy to convert to heat energy.

Explanation:
The chapter explains that different conductors offer different levels of resistance to current flow. Nichrome wire has higher resistance than copper, so when current flows through it, the resistance causes electrical energy to be converted into heat energy, making the wire warm.

Question: What is the main structural difference between a Voltaic cell and a dry cell?
A. A Voltaic cell uses two metal rods and a liquid electrolyte, while a dry cell uses a zinc container and paste-like electrolyte.
B. A Voltaic cell is rechargeable, but a dry cell is not.
C. A Voltaic cell produces more current than a dry cell.
D. There is no structural difference; they are the same device with different names.
Show Answer & Explanation

Answer: (A) A Voltaic cell uses two metal rods and a liquid electrolyte, while a dry cell uses a zinc container and paste-like electrolyte.

Explanation:
According to the chapter, a Voltaic cell contains two metal electrodes and a liquid electrolyte (weak acid or salt solution), whereas a dry cell has a zinc container (negative terminal) and a carbon rod covered with a metal cap (positive terminal) surrounded by a paste-like electrolyte.

Question: In the lemon cell activity, when students connect multiple lemons in series and the LED glows, what role does the lemon juice play in this setup?
A. It acts as the electrical power source.
B. It serves as the electrolyte that enables electrical conduction between the electrodes.
C. It prevents the copper and iron from oxidizing.
D. It generates heat that powers the LED.
Show Answer & Explanation

Answer: (B) It serves as the electrolyte that enables electrical conduction between the electrodes.

Explanation:
The lemon juice acts as an electrolyte—a conductor that allows ions to move between the copper wire (positive electrode) and iron nail (negative electrode), completing the circuit and allowing current to flow through the LED.

Question: Based on the chapter's discussion about the Earth's magnetism, how is Earth's magnetic field generated?
A. Permanent magnets buried deep within the Earth produce the field.
B. The rotation of Earth creates the magnetic field.
C. Movement of liquid iron in Earth's core creates electric currents that generate the magnetic field.
D. Radioactive minerals in Earth's crust produce magnetic radiation.
Show Answer & Explanation

Answer: (C) Movement of liquid iron in Earth's core creates electric currents that generate the magnetic field.

Explanation:
The 'A step further' section explicitly states that deep inside the Earth, the movement of liquid iron in the core creates electric currents, which in turn generate a magnetic field. This is analogous to how electricity can produce magnetism, which is the main principle discussed throughout the chapter.

Question: When an electromagnet is used in practical applications like lifting scrap metal, why is it advantageous to turn the current ON and OFF with a switch rather than using a permanent magnet?
A. It saves electricity because the magnet is only active when needed.
B. The electromagnet strength cannot be adjusted, so switching is necessary.
C. Turning the current off makes the magnetic field disappear, allowing the objects to be released.
D. Permanent magnets are too heavy to be used in cranes.
Show Answer & Explanation

Answer: (C) Turning the current off makes the magnetic field disappear, allowing the objects to be released.

Explanation:
The chapter explains that in lifting electromagnets, the operator can control the magnet by switching the current ON and OFF. When current is on, the electromagnet lifts objects; when switched off, the magnetic field disappears and objects are released. This control is not possible with permanent magnets.

Question: In the experiment where students compared heating with one cell versus two cells using the same nichrome wire for 30 seconds, what conclusion can be drawn?
A. The amount of heat generated depends only on the wire's material and length.
B. More cells provide a greater amount of current, producing more heat.
C. Two cells generate less heat because they divide the current between them.
D. The number of cells does not affect the heating of the wire.
Show Answer & Explanation

Answer: (B) More cells provide a greater amount of current, producing more heat.

Explanation:
The 'Think like a scientist' section states that with 2 cells, more heat is generated than with 1 cell because the heat generated depends on the magnitude of the electric current. A battery with more cells provides a larger current, which creates more heat.

Question: If a student reverses the battery terminals in an electromagnet setup, what would happen to the electromagnet's properties?
A. The electromagnet would stop working immediately.
B. The strength of the electromagnet would decrease.
C. The poles of the electromagnet would be reversed.
D. The electromagnet would become a permanent magnet.
Show Answer & Explanation

Answer: (C) The poles of the electromagnet would be reversed.

Explanation:
The chapter states that an electromagnet's poles can be reversed by changing the direction of the current. Reversing the battery terminals changes the direction of current flow, which causes the magnetic poles to switch positions—what was a north pole becomes a south pole and vice versa.

Question: Household electrical appliances like heaters and kettles operate on the heating effect of electric current. However, the chapter mentions safety concerns related to this effect. What is one such concern?
A. The devices become too bright when heated.
B. Overheating in appliances may damage plugs and sockets, or cause fires if not properly managed.
C. The heating effect only works in cold climates.
D. Heating appliances cannot be used safely in homes.
Show Answer & Explanation

Answer: (B) Overheating in appliances may damage plugs and sockets, or cause fires if not properly managed.

Explanation:
• The heating effect can cause energy loss in transmission wires
• Overheating may cause plastic parts in plugs and sockets to melt
• This can potentially lead to fires
• Safety devices are installed in household circuits to minimize these incidents

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