Electricity: Magnetic and Heating Effects
Each subtopic includes About section, revision page link, 10 preview questions, and practice CTAs.
Heating Effect of Electric Current
SubtopicHeating Effect of Electric Current under Electricity: Magnetic and Heating Effects for Grade 8 CBSE.
Preview questions (no answers)
- 1.
The presence of argon or nitrogen gas inside an electric bulb is intended to:
A.Make the bulb colorful
B.Prevent the filament from burning out
C.Increase the current
D.Reduce the light produced
- 2.
Why does the bulb of an electric torch not get as hot as a room heater?
A.It uses more current
B.It has very low resistance and current
C.It is made of wood
D.It has no heating element
- 3.
What happens to the heating element immediately after the switch is turned off?
A.It gets hotter
B.It starts cooling down
C.It continues to glow
D.It melts
- 4.
Which of the following will produce the most heat if the same current flows through them for 5 minutes?
A.A short thick copper wire
B.A long thin nichrome wire
C.A short thick silver wire
D.A long thick aluminum wire
- 5.
If you replace a 5A fuse with a copper wire of the same thickness, what is the most likely danger?
A.The circuit will not work at all
B.The copper wire will melt too quickly
C.The copper wire will not melt during a current surge, potentially causing a fire
D.The appliances will use less electricity
- 6.
Which of the following is NOT an application of the heating effect of current?
A.Electric Oven
B.Electric Room Heater
C.Electric Fan
D.Electric Press
- 7.
The 'heating element' in an appliance is the part that:
A.Transfers electricity to the plug
B.Converts electrical energy into heat
C.Protects the user from electric shock
D.Controls the amount of current entering the device
- 8.
A fuse is always connected in 'series' with the live wire. If it were connected in 'parallel' with an appliance, what would happen?
A.The fuse would protect the appliance better.
B.The fuse would create a short circuit and blow immediately when the power is on.
C.The appliance would consume less power.
D.The heating effect would be eliminated.
- 9.
What is the role of 'Mica' in an electric iron in relation to the heating effect?
A.It is a good conductor of electricity and heat.
B.It is a poor conductor of electricity but a good conductor of heat.
C.It is a good conductor of electricity but a poor conductor of heat.
D.It is a poor conductor of both electricity and heat.
- 10.
Which part of an electric bread toaster is responsible for the 'Heating Effect' that toasts the bread?
A.The plastic outer casing.
B.The spring mechanism.
C.The nichrome ribbons wound around mica sheets.
D.The copper power cord.
Download the worksheet for Electricity: Magnetic and Heating Effects - Heating Effect of Electric Current to practice offline. It includes additional chapter-level practice questions.
Electric Fuse and Safety Devices
SubtopicElectric Fuse and Safety Devices under Electricity: Magnetic and Heating Effects for Grade 8 CBSE.
Preview questions (no answers)
- 1.
To protect a household circuit from damage caused by excess current, a safety device like a fuse must be placed where it can monitor the total current flow. In the following diagram, at which position should the fuse be installed to protect both the bulb and the heater simultaneously?
A.At Point X (Main Line)
B.Only in the wire connected to the Bulb
C.Only in the wire connected to the Heater
D.At the very end of the heater's connection
- 2.
When a fuse blows, it means the circuit has become:
A.Closed
B.Broken
C.Short-circuited and dangerous
D.More efficient
- 3.
Why do we use copper for connecting wires in household circuits?
A.It is a very good conductor of electricity
B.It is a very good insulator
C.It has a very low melting point
D.It is magnetic
- 4.
What prevents a fuse from catching fire when it melts?
A.It is enclosed in a non-combustible casing like porcelain
B.It is kept in water
C.It is made of wood
D.It never gets hot enough
- 5.
What is the primary reason why we see light from an electric bulb when current passes through its filament?
A.The filament creates a magnetic field that glows.
B.The filament is heated to such a high temperature that it starts glowing.
C.The gas inside the bulb reacts with the electricity.
D.The current itself is a form of light.
- 6.
Which of the following is NOT a safety component in a domestic electrical circuit?
A.Earth wire
B.Fuse
C.MCB
D.Electromagnet
- 7.
A student makes an electromagnet using a copper wire and an iron nail. If they replace the iron nail with a glass rod, what will happen?
A.The glass rod will become a stronger magnet.
B.The glass rod will not become a magnet.
C.The glass rod will melt due to the current.
D.The glass rod will attract only plastic objects.
- 8.
A technician wants to make a fuse that blows at a lower current. He should use a wire that is:
A.Thinner and made of the same material.
B.Thicker and made of the same material.
C.Shorter and made of the same material.
D.Made of a material with a higher melting point.
- 9.
An electric bell is working. What energy transformation is taking place in the electromagnet part of the bell?
A.Electrical energy Mechanical energy
B.Electrical energy Magnetic energy
C.Magnetic energy Sound energy
D.Chemical energy Electrical energy
- 10.
Which of the following statements about the magnetic field of a current-carrying straight wire is FALSE?
A.The field lines are concentric circles.
B.The direction of the field depends on the direction of the current.
C.The magnetic field is strongest at the center of the wire's cross-section.
D.The field strength decreases as we move away from the wire.
Download the worksheet for Electricity: Magnetic and Heating Effects - Electric Fuse and Safety Devices to practice offline. It includes additional chapter-level practice questions.
Magnetic Effect of Electric Current: Oersted’s Observation
SubtopicMagnetic Effect of Electric Current: Oersted’s Observation under Electricity: Magnetic and Heating Effects for Grade 8 CBSE.
Preview questions (no answers)
- 1.
The magnetic effect of current was discovered ________.
A.Deliberately after many years of search
B.By accident during a lecture
C.While studying the stars
D.While inventing the telephone
- 2.
If the needle does not deflect when the switch is closed, what could be the reason?
A.The battery is dead
B.The wire is broken
C.The needle is jammed
D.Any of the above
- 3.
The phenomenon where a compass needle moves due to current is the basis for making an ________.
A.Electric heater
B.Electromagnet
C.Electric oven
D.Electric bulb
- 4.
What happens to the needle if the current in the circuit is doubled?
A.It deflects more
B.It deflects less
C.It stops moving
D.It points only towards the battery
- 5.
In Oersted's observation, when a steady current flows through a wire placed above a compass, the needle deflects and soon comes to rest at a specific new angle. What is the primary reason the needle stops at this fixed position instead of rotating continuously?
A.The magnetic field produced by the electric current is only momentary and disappears once the needle moves.
B.The friction at the needle's pivot is the only force that eventually stops the needle's motion.
C.The needle reaches a state of equilibrium where the magnetic field of the wire and the Earth's magnetic field balance each other.
D.The magnetic needle loses its magnetism temporarily due to the heat generated by the wire.
- 6.
Which of the following describes the nature of the force that deflects the compass needle?
A.Electrostatic force
B.Gravitational force
C.Magnetic force
D.Frictional force
- 7.
If a compass needle is placed near a wire and the current is increased by adding more cells in series, what happens to the deflection?
A.The deflection decreases
B.The deflection increases
C.The deflection remains the same
D.The needle points to the South pole
- 8.
Oersted's observation showed that a current-carrying wire behaves like a magnet. Does this mean the wire will attract small non-magnetized iron filings?
A.No, only permanent magnets can attract iron filings.
B.Yes, the wire will attract iron filings just like a bar magnet.
C.Only if the wire is made of iron or steel.
D.Yes, but only if the wire is insulated.
- 9.
If you use a compass with a very weak internal magnet for Oersted's experiment, how will the deflection angle compare to a standard compass for the same current?
A.The angle will be larger.
B.The angle will be smaller.
C.The angle will be the same, but the needle will move slower.
D.The needle will not move at all.
- 10.
Why is the deflection of the compass needle usually small in a standard classroom Oersted experiment using a single cell?
A.The Earth's magnetic field is very strong compared to the field produced by a small current.
B.Magnetic fields from wires are always weak regardless of current.
C.The copper wire absorbs the magnetic field lines.
D.The compass needle is too heavy to move.
Download the worksheet for Electricity: Magnetic and Heating Effects - Magnetic Effect of Electric Current: Oersted’s Observation to practice offline. It includes additional chapter-level practice questions.
Electromagnets: Construction and Uses
SubtopicElectromagnets: Construction and Uses under Electricity: Magnetic and Heating Effects for Grade 8 CBSE.
Preview questions (no answers)
- 1.
The discovery that electric current can produce magnetism was made by observing the movement of a ______.
A.Clock
B.Magnetic compass needle
C.Thermometer
D.Barometer
- 2.
In an electric bell, the hammer is attached to a flexible metal strip called the:
A.Armature
B.Gong
C.Switch
D.Battery terminal
- 3.
If the insulation of the wire in an electromagnet is damaged and the wires touch each other, it might cause a:
A.Better magnet
B.Short circuit
C.Cooler wire
D.Stronger battery
- 4.
Which device is used to 'open' or 'close' the circuit for an electromagnet?
A.Wire
B.Bulb
C.Switch
D.Core
- 5.
In an electromagnet, the magnetic field lines inside the solenoid are:
A.Circular
B.Parallel straight lines
C.Intersecting each other
D.Randomly distributed
- 6.
Which of the following is a common application of electromagnets in daily life security systems?
A.Magnetic door locks
B.Smoke detectors
C.Glass windows
D.Solar panels
- 7.
In a circuit containing an electromagnet, a rheostat (variable resistor) is added. If the resistance is increased, the magnetic strength will:
A.Increase
B.Decrease
C.Stay the same
D.Reverse
- 8.
If the current in an electromagnet is kept constant, but the number of turns is increased from to , what happens to the magnetic field strength?
A.It becomes three times stronger.
B.It becomes nine times stronger.
C.It remains the same because current is constant.
D.It becomes three times weaker.
- 9.
In industrial scrap sorting, how does an electromagnet distinguish between iron and aluminum?
A.Aluminum is attracted more strongly than iron.
B.Iron is ferromagnetic and is attracted, while aluminum is not and is left behind.
C.The electromagnet changes polarity when it touches aluminum.
D.Aluminum causes the electromagnet to turn off automatically.
- 10.
What is the function of the soft iron armature in an electric bell?
A.To produce the sound when it hits the gong.
B.To act as a bridge that is attracted by the electromagnet to move the hammer.
C.To provide the electrical resistance needed for the circuit.
D.To house the battery and switch.
Download the worksheet for Electricity: Magnetic and Heating Effects - Electromagnets: Construction and Uses to practice offline. It includes additional chapter-level practice questions.
Working of an Electric Bell
SubtopicWorking of an Electric Bell under Electricity: Magnetic and Heating Effects for Grade 8 CBSE.
Preview questions (no answers)
- 1.
When the armature is pulled by the electromagnet, which part is hit by the hammer?
A.Contact screw
B.Soft iron core
C.Gong
D.Spring
- 2.
In an electric bell, the magnetism is produced only when:
A.The hammer hits the gong
B.The current flows through the coils
C.The battery is new
D.The switch is open
- 3.
What is the role of the iron core inside the coils?
A.To stop the current
B.To increase the strength of the magnetic field
C.To act as a hammer
D.To provide sound
- 4.
The repetitive action in a bell is known as the _____ mechanism.
A.Push and pull
B.Make and break
C.Heat and cold
D.Fast and slow
- 5.
In a standard electric bell circuit, the contact screw and the armature's springy metal strip are designed to touch and separate repeatedly. If these two components were permanently joined together with a conductive wire (bypassing the contact point), what would be the result when the switch is pressed?
A.The armature would vibrate much faster than usual, making a high-pitched sound.
B.The hammer would strike the gong once and remain stuck toward the electromagnet.
C.The bell would not ring at all because the circuit would become an open circuit.
D.The electromagnet would lose its magnetism immediately due to the permanent connection.
- 6.
What is the purpose of using insulated wire for the coil in an electric bell?
A.To prevent heat from escaping
B.To ensure that the current flows through the length of the wire and not directly through the core
C.To make the wire more flexible
D.To protect the user from electric shock only
- 7.
Which part of the electric bell ensures that the circuit is 'broken' periodically?
A.The battery
B.The movement of the armature away from the contact screw
C.The switch
D.The gong
- 8.
In a diagram of an electric bell, if the wire is broken between the electromagnet and the contact screw, what will be the result?
A.The bell will ring continuously.
B.The electromagnet will still work, but the hammer won't move.
C.The circuit will be incomplete, and the bell will not function.
D.The battery will overheat.
- 9.
How does the 'Magnetic Effect of Current' differ from the 'Heating Effect of Current' in the context of an electric bell?
A.The magnetic effect is essential for the bell to work, while the heating effect is a wasted byproduct.
B.The heating effect moves the hammer, while the magnetic effect resets the screw.
C.The magnetic effect depends on resistance, while the heating effect depends on turns.
D.There is no heating effect in an electric bell.
- 10.
What would happen if the electromagnet in the bell was a permanent magnet instead?
A.The hammer would strike the gong and stay there; the bell would not ring repeatedly.
B.The bell would ring continuously as long as the battery is connected.
C.The hammer would be repelled away from the gong.
D.The permanent magnet would lose its magnetism immediately.
Download the worksheet for Electricity: Magnetic and Heating Effects - Working of an Electric Bell to practice offline. It includes additional chapter-level practice questions.
Does an Electric Current Have a Magnetic Effect?
SubtopicDoes an Electric Current Have a Magnetic Effect? under Electricity: Magnetic and Heating Effects for Grade 8 CBSE.
Preview questions (no answers)
- 1.
Electromagnets can be made very strong to lift many tonnes of weight. This makes them useful in:
A.Toy shops
B.Scrapyards
C.Kitchens
D.Libraries
- 2.
Magnetic effect of current is discovered by chance by Hans Christian Oersted while he was:
A.Teaching a class
B.Sleeping
C.Eating
D.Building a house
- 3.
Why is tungsten used in bulbs?
A.It is very cheap
B.It has a very high melting point
C.It is a liquid at room temperature
D.It is magnetic
- 4.
The symbol for a battery consists of:
A.A single long and short line
B.Two or more cells connected in series
C.A circle with a cross
D.A wavy line
- 5.
A student conducts an experiment where they wind an insulated copper wire around a plastic tube instead of an iron nail. When the switch is turned ON, the student observes that the setup cannot lift iron pins, but a magnetic compass placed nearby shows a deflection. What does this experiment demonstrate?
A.The magnetic effect of an electric current can only be produced when using a metallic core.
B.The magnetic field is an inherent property of the electric current itself, regardless of the core material.
C.Plastic becomes a magnetic material when an electric current flows through a wire wrapped around it.
D.The deflection of the compass needle is caused by the heat produced in the wire, not by magnetism.
- 6.
The magnetic field around a current-carrying wire exists:
A.Only when the wire is very hot
B.Only when the circuit is closed and current flows
C.All the time, even when the battery is removed
D.Only in a vacuum
- 7.
Which of the following would produce the strongest magnetic field?
A.A straight wire with 1A current
B.A coil with 10 turns and 1A current
C.A coil with 100 turns and 1A current
D.A coil with 100 turns and 0.1A current
- 8.
What is the effect of increasing the 'frequency' of the make-and-break cycle in an electric bell?
A.The sound becomes a higher pitch.
B.The sound becomes louder.
C.The hammer strikes the gong more times per second.
D.The electromagnet becomes weaker.
- 9.
A student makes two electromagnets. Electromagnet A has 50 turns and 2A current. Electromagnet B has 100 turns and 1A current. Which one is stronger?
A.Electromagnet A is stronger.
B.Electromagnet B is stronger.
C.They are approximately equal in strength.
D.Strength cannot be determined without knowing the core material.
- 10.
A magnetic crane in a scrapyard is picking up a large iron beam. If the generator providing current fails, what will happen to the beam?
A.It will remain attached because of residual magnetism.
B.It will drop immediately because the electromagnet loses its magnetism.
C.It will slowly descend.
D.It will become permanently magnetized and stay stuck.
Download the worksheet for Electricity: Magnetic and Heating Effects - Does an Electric Current Have a Magnetic Effect? to practice offline. It includes additional chapter-level practice questions.
Electromagnets
SubtopicElectromagnets under Electricity: Magnetic and Heating Effects for Grade 8 CBSE.
Preview questions (no answers)
- 1.
The magnetic effect of current was discovered by observing the deflection of a:
A.Bar magnet
B.Magnetic compass needle
C.Iron nail
D.Copper plate
- 2.
Which device automatically turns off the supply when there is a fault in the circuit?
A.Switch
B.MCB
C.Generator
D.Transformer
- 3.
What happens to the heating effect if the current in a wire is increased?
A.Heat produced increases
B.Heat produced decreases
C.No heat is produced
D.Heat becomes cold
- 4.
Which of the following can be used to detect current in a circuit if a bulb is too dim to glow?
A.An eraser
B.A magnetic compass
C.A piece of wood
D.A plastic ruler
- 5.
Which of the following components is used to measure the amount of electric current flowing in a circuit?
A.Voltmeter
B.Ammeter
C.Galvanometer
D.Ohm meter
- 6.
What happens when the switch is in the 'OFF' position in a circuit?
A.The circuit is closed and current flows
B.The circuit is open and no current flows
C.The circuit is closed and no current flows
D.The circuit is open and current flows
- 7.
In an electromagnet, the strength of the magnetic field can be increased by:
A.Increasing the current
B.Increasing the number of turns of wire
C.Using a soft iron core
D.All of the above
- 8.
Which scientist first discovered the magnetic effect of electric current?
A.James Watt
B.Hans Christian Oersted
C.Michael Faraday
D.Thomas Edison
- 9.
If you reverse the terminals of the battery connected to an electric bell, what will happen to its operation?
A.The bell will not ring at all.
B.The hammer will strike the gong with more force.
C.The bell will ring normally because the electromagnet works regardless of polarity.
D.The bell will ring in the opposite direction.
- 10.
In which of the following cases will the heating effect be most pronounced?
A.Low current and low resistance.
B.High current and high resistance.
C.High current and low resistance.
D.Low current and high resistance.
Download the worksheet for Electricity: Magnetic and Heating Effects - Electromagnets to practice offline. It includes additional chapter-level practice questions.
Lifting electromagnets
SubtopicLifting electromagnets under Electricity: Magnetic and Heating Effects for Grade 8 CBSE.
Preview questions (no answers)
- 1.
A lifting electromagnet is often used to separate which metal from aluminum cans?
A.Gold
B.Silver
C.Iron/Steel
D.Copper
- 2.
If you reverse the direction of current in an electromagnet, what happens to its poles?
A.They disappear
B.They remain the same
C.They are reversed
D.They become stronger
- 3.
The 'Magnetic Effect of Current' means that a wire carries a magnetic field only when ________.
A.It is cold
B.It is hot
C.Current flows through it
D.It is painted red
- 4.
Is an electromagnet a permanent magnet?
A.Yes
B.No
C.Only if it is made of iron
D.Only if it is very large
- 5.
What effect does increasing the diameter of the iron core have on a lifting electromagnet's performance?
A.It generally allows for a stronger magnetic field up to a saturation point
B.It makes the magnet weaker
C.It has no effect on magnetism
D.It turns the magnet into an insulator
- 6.
Which material would be best to use as a 'fuse' wire to protect the lifting electromagnet's circuit from overheating?
A.A material with a very high melting point
B.A material with a low melting point
C.Copper
D.Silver
- 7.
A crane operator finds that some iron pieces are sticking to the electromagnet even after switching off the current. This suggests that:
A.The current is still leaking
B.The core material has high retentivity (like steel)
C.The iron scrap is magnetized
D.The gravity is low
- 8.
A crane lifting electromagnet uses a DC supply. What would be the effect of ripples (fluctuations) in the DC voltage?
A.The magnet would rotate rapidly.
B.The lifting force would fluctuate, potentially causing the load to vibrate or slip.
C.The magnet would start producing a high-pitched sound but lift perfectly.
D.The scrap metal would be repelled every few seconds.
- 9.
Why do the coils of a lifting electromagnet exert a 'bursting force' on themselves when carrying a very high current?
A.Because the wires are trying to get closer to the core.
B.Because parallel wires carrying current in the same direction attract, but opposite sides of the coil carry current in opposite directions and repel.
C.Because the heat makes the copper expand rapidly.
D.Because of the air pressure inside the magnet.
- 10.
In an electromagnet, the magnetic field strength () inside the core is given by . What does represent?
A.The resistance of the wire.
B.The magnetic permeability of the core material.
C.The speed of light in the core.
D.The number of turns per unit length.
Download the worksheet for Electricity: Magnetic and Heating Effects - Lifting electromagnets to practice offline. It includes additional chapter-level practice questions.
Does a Current Carrying Wire Get Hot?
SubtopicDoes a Current Carrying Wire Get Hot? under Electricity: Magnetic and Heating Effects for Grade 8 CBSE.
Preview questions (no answers)
- 1.
When electric current flows through a coil, it creates a ________ around it.
A.Electric field only
B.Magnetic field
C.Vacuum
D.Water field
- 2.
Who is famous for the 'Compass Needle' experiment?
A.Galileo
B.Oersted
C.Newton
D.Dalton
- 3.
The phenomenon where a wire melts and breaks due to excessive current is used in a:
A.Switch
B.Fuse
C.Cell
D.Bulb
- 4.
Which of the following does NOT result in the heating of a wire?
A.High current
B.High resistance
C.Switching the current off
D.Thin wire
- 5.
If you bring a bar magnet near a current-carrying wire, what will happen?
A.Nothing will happen
B.The wire and magnet will exert a force on each other
C.The wire will melt instantly
D.The magnet will lose its magnetism permanently
- 6.
A fuse wire has a specific 'current rating'. This means:
A.The maximum voltage it can handle
B.The maximum current that can safely flow through it
C.The time it takes to melt
D.The length of the wire
- 7.
The magnetic effect of electric current is used in:
A.Electric heaters
B.Electric fuses
C.Cranes used to move scrap iron
D.Immersion rods
- 8.
A fuse wire is rated 10A. If the circuit it protects suddenly draws 15A, what happens to the wire and why?
A.It melts because the rate of heat production exceeds the rate of heat dissipation
B.It becomes a magnet and breaks the circuit via magnetic force
C.It expands and disconnects from the terminal without melting
D.It glows brighter but allows the current to pass to avoid interruption
- 9.
A magnetic compass is placed near a wire. As the current in the wire is gradually increased, the deflection of the compass needle:
A.Increases linearly with current
B.Decreases as current increases
C.Remains constant once it deflects
D.Reverses direction at high currents
- 10.
Which component in an electric bell is responsible for converting electrical energy into mechanical movement?
A.The Electromagnet
B.The Gong
C.The Switch
D.The Contact Screw
Download the worksheet for Electricity: Magnetic and Heating Effects - Does a Current Carrying Wire Get Hot? to practice offline. It includes additional chapter-level practice questions.
How Does a Battery Generate Electricity?
SubtopicHow Does a Battery Generate Electricity? under Electricity: Magnetic and Heating Effects for Grade 8 CBSE.
Preview questions (no answers)
- 1.
Electric current is the flow of:
A.Atoms
B.Protons
C.Electrons
D.Neutrons
- 2.
Which of these is a source of electric current?
A.Bulb
B.Switch
C.Cell
D.Wire
- 3.
When you turn off the switch in a room, you are ________ the circuit.
A.Closing
B.Completing
C.Opening
D.Shortening
- 4.
How many terminals does a standard electric cell have?
A.One
B.Two
C.Three
D.Four
- 5.
How does a battery 'die' or become exhausted?
A.It loses all its electrons to the air
B.The chemicals inside are used up and the reaction stops
C.The wires inside the battery melt
D.The magnet inside loses its strength
- 6.
Which of these factors does NOT affect the magnitude of the magnetic field produced by a straight current-carrying wire?
A.Current in the wire
B.Distance from the wire
C.Thickness of the insulation
D.Nature of the medium around it
- 7.
An electromagnet is a:
A.Permanent magnet
B.Natural magnet
C.Temporary magnet
D.Non-magnetic material
- 8.
Which energy transformation takes place in an electromagnet?
A.Magnetic energy to Electrical energy
B.Electrical energy to Magnetic energy
C.Chemical energy to Light energy
D.Mechanical energy to Electrical energy
- 9.
The melting point of a fuse wire should be:
A.Higher than the melting point of the connecting wires.
B.Lower than the melting point of the connecting wires.
C.Exactly the same as the connecting wires.
D.Infinite.
- 10.
What happens if the current in an electromagnet is increased while the number of turns is kept constant?
A.The magnetic field strength increases.
B.The magnetic field strength decreases.
C.The magnetic poles reverse.
D.Nothing happens to the magnetic field.
Download the worksheet for Electricity: Magnetic and Heating Effects - How Does a Battery Generate Electricity? to practice offline. It includes additional chapter-level practice questions.
Voltaic cell
SubtopicVoltaic cell under Electricity: Magnetic and Heating Effects for Grade 8 CBSE.
Preview questions (no answers)
- 1.
The flow of conventional current in a circuit connected to a Voltaic cell is from:
A.Negative terminal to Positive terminal
B.Copper plate to Zinc plate
C.Zinc plate to Copper plate
D.Electrolyte to Zinc plate
- 2.
What happens to the Zinc plate in a Voltaic cell over time during discharge?
A.It gets thicker
B.It remains unchanged
C.It gradually dissolves into the electrolyte
D.It turns into copper
- 3.
Which of these is a major disadvantage of a simple Voltaic cell for practical use?
A.It is too expensive
B.It produces very high voltage
C.It suffers from local action and polarization
D.It uses solid electrolytes
- 4.
When a wire connects the two plates of a Voltaic cell, in which direction do the electrons flow in the external circuit?
A.From Copper to Zinc
B.From Zinc to Copper
C.From Electrolyte to Copper
D.They do not flow
- 5.
To convert a Voltaic cell into a practical battery, which component is usually added to prevent polarization in modern variations like the Daniell cell?
A.A switch
B.A depolarizer (like Copper Sulfate)
C.More sulfuric acid
D.A thicker Zinc plate
- 6.
Which of the following describes the 'Local Action' defect in a voltaic cell?
A.Hydrogen gas preventing current flow
B.Formation of small cells on the Zinc surface due to impurities
C.The cell heating up too much
D.The electrolyte turning into a solid
- 7.
Why does the current from a simple Voltaic cell decrease rapidly after some time?
A.The Zinc is all gone
B.The electrolyte evaporates
C.Hydrogen bubbles increase the internal resistance (Polarization)
D.The Copper plate becomes negative
- 8.
Consider a voltaic cell where the electrolyte is a paste rather than a liquid (similar to a dry cell). If the paste dries out over time, how will the magnetic effect produced by a wire connected to this cell change when placed near a compass needle?
A.The compass needle will deflect more because dry paste is a better conductor
B.The compass needle will not deflect because the lack of moisture prevents ion movement, stopping the current
C.The magnetic effect will become permanent even after the wire is disconnected
D.The deflection will remain constant because the electrodes are still metal
- 9.
A student compares two cells: Cell A (Zinc and Copper in ) and Cell B (Zinc and Silver in ). Both are connected to identical heating coils. Why does the coil connected to Cell B get hotter than the coil connected to Cell A in the same amount of time?
A.Silver is a better conductor of heat than Copper
B.The chemical potential difference between Zn and Ag is greater than between Zn and Cu
C.Cell B produces AC current which generates more heat than DC
D.Silver ions in the electrolyte provide less resistance than Copper ions
- 10.
A technician uses a voltaic cell to create a temporary electromagnet. They find that after a short duration, the magnetic field strength weakens. Upon inspection, they see the Zinc electrode has thinned and 'pitted' even in areas not connected to the wire. This waste of material is primarily due to:
A.The magnetic field stripping atoms off the electrode surface
B.Small local circuits formed between Zinc and impurities on its surface
C.The heating effect of the current melting the Zinc metal
D.Oxygen from the air reacting with the Copper electrode
Download the worksheet for Electricity: Magnetic and Heating Effects - Voltaic cell to practice offline. It includes additional chapter-level practice questions.
Dry cells
SubtopicDry cells under Electricity: Magnetic and Heating Effects for Grade 8 CBSE.
Preview questions (no answers)
- 1.
In a common dry cell used in flashlights, which component acts as the negative terminal (anode)?
A.Carbon rod
B.Manganese dioxide paste
C.Zinc container
D.Ammonium chloride solution
- 2.
Which of these is a safety device based on the heating effect of current?
A.Electric bell
B.Electric fuse
C.Electromagnet
D.Dry cell
- 3.
Which scientist discovered the magnetic effect of electric current?
A.Isaac Newton
B.Hans Christian Oersted
C.Thomas Edison
D.James Watt
- 4.
In a dry cell, the carbon rod is topped with a brass cap. This cap serves as the:
A.Positive terminal
B.Negative terminal
C.Insulator
D.Electrolyte
- 5.
In an electromagnet powered by a dry cell, the core is usually made of:
A.Steel
B.Soft Iron
C.Copper
D.Aluminum
- 6.
Why is a dry cell not rechargeable?
A.It doesn't have enough chemicals
B.The chemical reactions are irreversible
C.The carbon rod is too thick
D.The zinc container is too thin
- 7.
The heating effect of current in a dry cell circuit depends on:
A.Only the voltage
B.Only the resistance
C.Both the current and the resistance
D.The color of the wire
- 8.
A heavy-duty dry cell is used to drive a motor. As the motor runs, the cell becomes warm. If the motor stalls (stops turning but remains connected), the cell gets much hotter. Why does the heating effect increase when the motor stalls?
A.The motor begins to act as a generator and sends current back to the cell.
B.The magnetic effect of the motor turns into thermal energy.
C.The back-EMF of the motor disappears, causing a massive increase in current through the cell's internal resistance.
D.The zinc in the cell reacts faster when the motor is not moving.
- 9.
While investigating a dry cell, a student notices that the carbon rod is surrounded by a black paste of and carbon powder. What is the specific purpose of adding carbon powder (charcoal) to the manganese dioxide?
A.To increase the voltage of the cell from to .
B.To prevent the zinc container from corroding too quickly.
C.To improve the electrical conductivity of the mixture.
D.To absorb moisture from the ammonium chloride paste.
- 10.
A series of dry cells is used to power a heating coil in a miniature heater. If the polarity of one of the four cells is reversed by mistake, what will be the effect on the heat produced by the coil ()?
A.The heat produced will increase because the reversed cell adds more resistance.
B.The heat produced will remain the same because the voltage is the same.
C.The heat produced will significantly decrease because the total effective voltage of the battery is reduced.
D.The coil will produce magnetic flux instead of heat.
Download the worksheet for Electricity: Magnetic and Heating Effects - Dry cells to practice offline. It includes additional chapter-level practice questions.
Rechargeable batteries
SubtopicRechargeable batteries under Electricity: Magnetic and Heating Effects for Grade 8 CBSE.
Preview questions (no answers)
- 1.
What is the benefit of using rechargeable batteries over dry cells?
A.They are cheaper to buy initially
B.They reduce environmental waste
C.They never run out of charge
D.They are made of paper
- 2.
When the switch is in the 'OFF' position, the circuit is said to be:
A.Closed
B.Open
C.Complete
D.Short
- 3.
Why do we use nichrome in heating appliances?
A.It has a low melting point
B.It has high resistance and high melting point
C.It is very cheap
D.It is a good magnet
- 4.
Secondary cells are used in:
A.Calculators (small button cells)
B.Toys (disposable dry cells)
C.Inverters and cars
D.Small flashlights
- 5.
The IS (International System) unit of electric current is:
A.Volt
B.Watt
C.Ampere
D.Joule
- 6.
Which metal is usually used to make the core of a powerful electromagnet?
A.Steel
B.Soft Iron
C.Aluminium
D.Copper
- 7.
When a current is passed through a coil of wire, the coil acts as a magnet. This coil is called a:
A.Insulator
B.Resistor
C.Solenoid
D.Capacitor
- 8.
What determines the polarity of the magnetic field produced by a solenoid?
A.The length of the solenoid.
B.The magnitude of the current.
C.The direction of the current flow through the coils.
D.The material of the wire's insulation.
- 9.
A fuse is rated at . If the voltage is , what is the maximum power that can be drawn through this fuse without it melting?
A.44 W
B.1100 W
C.220 W
D.25 W
- 10.
What is the purpose of using a 'parallel' circuit for home appliances in relation to the heating effect?
A.To ensure that if one appliance blows a fuse, the others keep working and that each gets the same voltage.
B.To increase the total resistance of the house to save money.
C.To make sure all appliances produce the same amount of heat.
D.To reduce the magnetic field interference between appliances.
Download the worksheet for Electricity: Magnetic and Heating Effects - Rechargeable batteries to practice offline. It includes additional chapter-level practice questions.