⚛️ Physics · Topic 6 of 10
Start with the study notes on Electric Current & its Effects (definitions, examples and a quick revision), then work through 60 practice questions, each with the correct answer and a clear explanation of why it is right. When you are ready, take this topic as an interactive quiz to test yourself.
Topic overview
When current flows, it can produce three effects:
Example: A heater (heating effect), an electric bell (magnetic effect) and electroplating (chemical effect).
Every wire carrying current gets warm. How much heat is produced depends on the material, length and thickness of the wire and on the amount of current.
Example: Electric irons, room heaters, toasters, kettles and geysers all use the heating effect.
The hot coil in a heater is made of nichrome, an alloy of nickel and chromium. It gets very hot without melting.
Example: The nichrome coil of a heater glows red-hot, while the copper wires leading to it stay fairly cool, because copper lets current through very easily.
A bulb's filament is made of tungsten, which can glow white-hot without melting. The glass bulb holds an unreactive gas, or no air at all, so the filament does not burn away.
Too much current makes wires dangerously hot. This happens with overloading (too many appliances on one circuit) or a short circuit (the live and neutral wires touching).
A fuse is a short wire with a low melting point, connected so that all the current passes through it. If the current becomes too large, the wire melts and breaks the circuit before the wiring overheats.
Remember: Replace a blown fuse with one of the correct rating, never with a thicker wire.
An MCB (miniature circuit breaker) does the same job, but it simply switches off. Once the fault is fixed, it can be switched back on.
In 1820, Hans Christian Oersted noticed that a compass needle moved when current flowed through a nearby wire. This showed that electric current produces a magnetic effect.
An electromagnet is a coil of insulated wire wound round a soft-iron core. It is a magnet only while current flows.
You can make it stronger by:
Examples:
When current flows, the electromagnet pulls an iron strip (the armature), and the hammer strikes the gong. This breaks the circuit, so the magnet lets go. The circuit closes again, and the cycle repeats very quickly.
Some liquids conduct electricity; others do not:
When current passes through a conducting liquid, it can cause chemical changes: gas bubbles at the metal rods (electrodes), a layer of metal on one rod, or a change of colour.
Example: Passing current through acidified water produces bubbles of hydrogen and oxygen.
Remember: An LED is better than a bulb for testing liquids, because it glows even with a very weak current.
Electroplating is coating an object with a thin layer of another metal using electricity. The object to be coated is connected to the negative terminal.
Examples:
| Misconception | Correct understanding |
|---|---|
| A thicker fuse wire is safer. | It may not melt during a fault, so the wiring can overheat and catch fire. |
| An electromagnet stays magnetic after it is switched off. | It is magnetic only while current flows. |
| All water conducts electricity well. | Distilled water is a poor conductor; the salts in tap water make it conduct. |
| Household copper wires get hot like a heater coil. | Copper lets current pass easily, so it stays cool; nichrome is chosen because it gets hot. |
| An MCB must be replaced after it trips. | An MCB is simply switched back on; a fuse must be replaced. |
Name the three effects of electric current.
The heating, magnetic and chemical effects.
Why is nichrome used in heaters?
It gets very hot without melting.
How does a fuse protect a house?
Its low-melting wire melts when the current is too high, which breaks the circuit.
Who discovered the magnetic effect of current?
Hans Christian Oersted, in 1820.
Give two ways to make an electromagnet stronger.
Use more turns of wire, and pass a bigger current.
Why does a scrap-yard crane use an electromagnet?
It can be switched off to drop the load.
In electroplating, which terminal is the object connected to?
The negative terminal.
Why are food cans coated with tin?
Tin stops the iron rusting and keeps food safe.
Key takeaway: One current, three effects: heat for heaters and fuses, magnetism for bells and cranes, and chemistry for electroplating.
Notes written by Velnov for Class 6–8 students, following the topics of the NCERT science syllabus.
Q1. easy
When electric current passes through a wire, the wire becomes hot. This is called the:
Answer: A — Heating effect of electric current
The heating effect of current is the production of heat when current flows through a wire. It is used in heaters, irons, geysers, toasters and bulbs.
Q57. easy
The three main effects of electric current are:
Answer: A — Heating, magnetic and chemical effects
Electric current can produce three effects: the heating effect (heaters, bulbs), the magnetic effect (electromagnets, bells) and the chemical effect (electroplating, electrolysis).
Q2. medium
Which of these appliances works on the HEATING effect of electric current?
Answer: A — Electric iron / room heater / toaster
Electric irons, room heaters, geysers, toasters and hair dryers all use the heating effect - current passes through a coil that becomes hot and produces heat.
Q5. medium
Why do the connecting wires of a heater (usually copper) NOT get very hot, while the nichrome coil does?
Answer: A — Copper has low resistance; nichrome has high resistance
Copper has very low resistance, so little heat is produced in it. Nichrome has high resistance, so it produces a lot of heat and glows - which is why it is used as the heating element.
Q6. medium
A device that protects electrical circuits and appliances by breaking the circuit when too much current flows is a/an:
Answer: A — Electric fuse
An electric fuse is a safety device. If the current becomes dangerously high (due to overloading or a short circuit), the fuse wire melts and breaks the circuit, preventing fires and damage.
Q8. medium
A modern safety device that automatically switches off the circuit during a fault (and can be reset instead of replaced) is a:
Answer: A — MCB (Miniature Circuit Breaker)
MCBs (Miniature Circuit Breakers) are switches that automatically turn off (trip) when the current is too high. Unlike a fuse (which must be replaced), an MCB can simply be switched back on after fixing the fault.
Q9. medium
The Danish scientist who discovered that an electric current produces a MAGNETIC effect was:
Answer: A — Hans Christian Oersted
In 1820, Hans Christian Oersted discovered that a compass needle placed near a current-carrying wire is deflected - showing that electric current produces a magnetic effect. This linked electricity and magnetism.
Q11. medium
A coil of insulated wire wound around an iron piece, which becomes a magnet only when current flows, is called an:
Answer: A — Electromagnet
An electromagnet is made by winding an insulated wire (coil) around a soft-iron core. When current flows, the iron becomes strongly magnetic; when the current stops, it loses its magnetism.
Q14. medium
Which of these uses an electromagnet?
Answer: A — An electric bell, cranes lifting scrap iron, and loudspeakers
Electromagnets are used in electric bells, cranes to lift heavy iron/steel scrap, loudspeakers, electric motors, and even by doctors to remove tiny iron pieces from the eye.
Q16. medium
An advantage of an electromagnet over a permanent magnet is that its magnetism can be:
Answer: A — Switched on and off, and its strength changed
An electromagnet's magnetism can be turned on or off (by controlling the current) and made stronger or weaker. This control makes it very useful in cranes, bells, motors and many machines.
Q17. medium
Doctors sometimes use an electromagnet to:
Answer: A — Remove small iron/steel splinters from a patient's eye
A small electromagnet can gently pull out tiny iron or steel splinters that have entered a patient's eye or body, because it attracts the magnetic metal without harming the surrounding tissue.
Q18. medium
Passing an electric current through some liquids can produce a CHEMICAL effect. Which of these is a sign of the chemical effect?
Answer: A — Bubbles of gas, deposits of metal, or colour changes at the electrodes
The chemical effect of current in a liquid can show up as gas bubbles forming, a metal being deposited on an electrode, or a change in colour of the liquid or electrodes.
Q19. medium
Liquids that ALLOW electric current to pass through them are called:
Answer: A — Conducting liquids (like salt water and acids)
Conducting liquids (such as salt solution, acids and bases) let current pass through, showing a chemical effect. Distilled (pure) water and oils do not conduct well.
Q22. medium
To detect a WEAK current passing through a liquid, it is better to use a ______ instead of a bulb.
Answer: A — LED (light-emitting diode)
An LED glows even with a very small current, so it is a better indicator than a bulb (which needs more current) when testing whether a liquid conducts electricity weakly. The LED must be connected the correct way round.
Q24. medium
Shiny CHROMIUM plating on car parts, taps and bicycle handles is done by electroplating because chromium:
Answer: A — Is shiny, does not rust easily, and resists scratches
Chromium has a shiny appearance, resists corrosion (rust) and scratches, and is hard. But chromium is expensive, so a thin layer is electroplated onto cheaper metals like iron to get these benefits at lower cost.
Q26. medium
Jewellery made of cheaper metal is often coated with a thin layer of gold or silver by electroplating to:
Answer: A — Give it the look of gold/silver at a lower cost
Gold and silver are costly. Electroplating a thin layer of them onto cheaper metal jewellery gives the appearance and shine of pure gold/silver at a much lower price.
Q28. medium
Which effect of current is used in an electric TOASTER?
Answer: A — Heating effect
A toaster uses the heating effect - current through a high-resistance coil produces heat that toasts the bread.
Q29. medium
Which effect of current is used in a crane that lifts scrap IRON in a junkyard?
Answer: A — Magnetic effect (electromagnet)
The crane uses a powerful electromagnet (the magnetic effect of current). Switched on, it lifts heavy iron scrap; switched off, it drops the load - very useful in junkyards and steel plants.
Q30. medium
Which effect of current is used in ELECTROPLATING?
Answer: A — Chemical effect
Electroplating uses the chemical effect of current - passing current through a solution deposits a metal layer on an object connected to the negative terminal.
Q32. medium
The filament of an electric bulb is usually made of which metal, because it can glow at high temperature without melting?
Answer: A — Tungsten
Bulb filaments are made of tungsten, which has a very high melting point. It can be heated until it glows white-hot to give light without melting.
Q34. medium
An electric FUSE is always connected in a circuit so that:
Answer: A — The whole current passes through it (in series with the appliance)
A fuse is connected in series so that all the current flows through it. If the current becomes too high, the fuse melts and breaks the whole circuit, protecting the appliance and wiring.
Q36. medium
A SHORT CIRCUIT (live and neutral wires touching directly) is dangerous because it causes:
Answer: A — A sudden very large current, which can overheat wires and start a fire
In a short circuit, current bypasses the appliance through a low-resistance path, so a huge current flows. This produces intense heat that can melt insulation and start fires. Fuses/MCBs protect against this.
Q38. medium
In electroplating, the object to be plated is connected to the ______ terminal of the battery.
Answer: A — Negative terminal
In electroplating, the article to be coated is made the cathode (connected to the negative terminal), so metal ions from the solution deposit onto it. The pure plating metal forms the anode (positive terminal).
Q40. medium
Which of the following statements about a fuse is TRUE?
Answer: A — It must be replaced after it melts (blows)
Once a fuse wire melts (blows) to protect the circuit, it must be replaced with a new one of the correct rating. An MCB, by contrast, can just be switched back on.
Q42. medium
An electric bell rings continuously because the circuit is repeatedly:
Answer: A — Made and broken by the movement of the armature
In an electric bell, when the electromagnet pulls the armature to strike the gong, it breaks the circuit; the magnet then releases the armature, closing the circuit again. This make-and-break repeats fast, so the bell rings continuously.
Q44. medium
Which safety practice helps prevent electrical fires at home?
Answer: A — Using proper fuses/MCBs and not overloading sockets
Using correctly rated fuses or MCBs and avoiding socket overloading prevents dangerous currents that cause fires. Bare wires and overloaded sockets are hazards to avoid.
Q46. medium
Which of these is an example of the chemical effect of electric current in daily life?
Answer: A — Electroplating of jewellery and car parts
Electroplating is a common use of the chemical effect. A glowing bulb and hot iron use the heating effect, and an electric bell uses the magnetic effect.
Q48. medium
Which of these correctly matches the appliance with the effect of current it uses?
Answer: A — Room heater - heating; electric bell - magnetic; electroplating - chemical
A room heater uses the heating effect, an electric bell uses the magnetic effect (electromagnet), and electroplating uses the chemical effect. Matching devices to effects is a common exam question.
Q50. medium
Which household appliance mainly uses the MAGNETIC effect of current?
Answer: A — Electric fan (motor)
An electric fan works by an electric motor, which uses the magnetic effect of current (interaction of magnets and current-carrying coils) to produce rotation. Geysers, irons and bulbs use the heating effect.
Q52. medium
Rubber gloves and rubber-soled shoes protect electricians because rubber is a/an:
Answer: A — Insulator (does not conduct electricity)
Rubber is an insulator, so it prevents current from passing through the electrician's body to the ground. This protects them from electric shocks while working with live wires.
Q54. medium
Which statement about LEDs is TRUE?
Answer: A — An LED glows only when connected the correct way and uses very little current
An LED (light-emitting diode) allows current in only one direction, so it glows only when connected correctly. It is energy-efficient, produces little heat and lasts long - which is why LEDs are used to detect weak currents and for modern lighting.
Q56. medium
The overall importance of studying the effects of electric current is that it explains how:
Answer: A — Everyday devices like heaters, bells, motors and electroplating work
The heating, magnetic and chemical effects of electric current explain the working of countless everyday devices - heaters, irons, bulbs, electric bells, motors, cranes, and electroplating processes - making this a very practical topic.
Q58. medium
A fuse melts and breaks the circuit when the current is:
Answer: A — Too high (more than the safe limit)
A fuse is a safety device with a low-melting-point wire. When the current rises above the safe limit (due to overload or short circuit), the fuse wire melts and breaks the circuit, preventing damage.
Q60. medium
Which of these is used to protect a house from damage due to excessive electric current?
Answer: A — A fuse or an MCB
Fuses and MCBs (miniature circuit breakers) protect household circuits by cutting off the supply when the current is dangerously high, preventing overheating and fire.
Q3. hard
The heating element (coil) of an electric heater is made of a special alloy called:
Answer: A — Nichrome
Nichrome (an alloy of nickel and chromium) has high resistance and a high melting point, so it becomes very hot without melting when current flows. It is used in heaters, toasters and irons.
Q4. hard
The amount of heat produced in a wire depends on:
Answer: A — The material, length and thickness of the wire, and the current
More heat is produced by a wire of higher resistance (which depends on its material, greater length, and smaller thickness) and by a larger current. This is why a thin high-resistance nichrome wire glows while thick copper wires do not.
Q7. hard
An electric fuse works because its wire is made of a material with a:
Answer: A — Low melting point (so it melts and breaks the circuit when current is too high)
The fuse wire is made of a metal/alloy with a low melting point (like a tin-lead alloy). When excessive current heats it, it melts quickly and breaks the circuit before the wiring or appliance is damaged.
Q10. hard
When a current-carrying wire is placed near a magnetic compass, the compass needle:
Answer: A — Deflects (moves) from its North-South position
A current-carrying wire behaves like a magnet and produces a magnetic field around it. This field deflects a nearby compass needle - Oersted's key observation showing the magnetic effect of current.
Q12. hard
The core of an electromagnet is made of SOFT IRON because soft iron:
Answer: A — Becomes a strong magnet with current but loses magnetism when current stops
Soft iron is used because it becomes strongly magnetic when current flows and quickly loses its magnetism when the current is switched off. This makes the electromagnet controllable (on/off).
Q13. hard
The strength of an electromagnet can be INCREASED by:
Answer: A — Increasing the number of turns in the coil and increasing the current
An electromagnet becomes stronger with more turns of wire in the coil and with a larger current flowing. A soft-iron core also makes it much stronger.
Q15. hard
In an electric bell, the electromagnet's job is to:
Answer: A — Attract an iron strip (armature) so the hammer strikes the gong repeatedly
In an electric bell, when current flows, the electromagnet attracts an iron armature, and the hammer hits the gong. This breaks the circuit, the magnet lets go, and the process repeats rapidly, making the bell ring continuously.
Q20. hard
Which of these liquids is a GOOD conductor of electricity?
Answer: A — Salt water (salt dissolved in water)
Salt water conducts electricity well because dissolved salt provides charged particles (ions). Pure distilled water, oils and kerosene are poor conductors of electricity.
Q21. hard
Pure distilled water is a POOR conductor of electricity, but ordinary tap water conducts because it contains:
Answer: A — Dissolved salts and minerals
Distilled water has no dissolved salts, so it barely conducts. Tap water contains dissolved salts and minerals that provide ions, allowing it to conduct electricity - which is why wet hands are dangerous near electricity.
Q23. hard
The process of depositing a layer of one metal over another using electricity is called:
Answer: A — Electroplating
Electroplating uses the chemical effect of current to coat an object with a thin layer of a desired metal (like chromium, silver, gold or tin). It improves appearance and protects against rust and wear.
Q25. hard
Tin cans used for storing food are made by electroplating TIN on iron because tin:
Answer: A — Is less reactive and prevents the iron from rusting and contaminating food
Iron would rust and spoil stored food. A thin layer of tin (which is less reactive and food-safe) is electroplated onto the iron, protecting the food and preventing rust - hence 'tin cans'.
Q27. hard
Coating iron with a layer of ZINC to protect it from rusting is called:
Answer: A — Galvanising
Galvanising is the coating of iron/steel with zinc to prevent rust. It can be done by electroplating or dipping in molten zinc. Galvanised iron sheets are used for roofs and buckets.
Q31. hard
In a circuit diagram, the standard symbol for a SWITCH in the OFF position is drawn as:
Answer: A — A gap in the line with a small lever (an open connection)
A switch is shown as a break in the circuit line with a small lever. When open (OFF), the line is broken; when closed (ON), it completes the line. (A circle with a cross is a bulb; unequal parallel lines are a cell.)
Q33. hard
Why is the filament of a bulb enclosed in a glass bulb filled with an inert gas (or a vacuum)?
Answer: A — To stop the hot filament from burning up (reacting with oxygen)
If the white-hot tungsten filament were exposed to air, it would quickly burn (react with oxygen) and break. So the bulb is either evacuated or filled with an inert gas (like argon) to protect the filament.
Q35. hard
Overloading (running too many high-power appliances on one circuit) can be dangerous because it:
Answer: A — Causes excessive current that can overheat wires and cause a fire
Too many appliances draw a large current, which overheats the wires (heating effect) and can cause a fire. Fuses and MCBs cut off the circuit to prevent this. Avoid plugging many appliances into one socket.
Q37. hard
When current is passed through acidified water, bubbles of gas form at the electrodes. This shows the:
Answer: A — Chemical effect of current (water splitting into hydrogen and oxygen)
Passing current through acidified water splits it into hydrogen and oxygen gases, which bubble off at the electrodes. This decomposition is a clear example of the chemical effect of current (electrolysis).
Q39. hard
The magnetic field produced by a current-carrying wire becomes stronger if you:
Answer: A — Increase the current in the wire
A larger current produces a stronger magnetic field around the wire. This principle is used in electromagnets, where increasing the current (and the number of coil turns) increases the magnetism.
Q41. hard
Which combination of effects can a single electric current show?
Answer: A — Heating, magnetic and chemical effects (depending on the circuit)
Electric current can produce a heating effect (in a wire), a magnetic effect (around a wire/coil), and a chemical effect (in a conducting liquid). Which effect is seen depends on the setup.
Q43. hard
Which of these liquids would make an LED in a tester glow, showing it conducts electricity?
Answer: A — Lemon juice (an acid)
Lemon juice is acidic and contains ions, so it conducts electricity and lights the LED. Oils and petrol are non-conducting (insulating) liquids and would not light the LED.
Q45. hard
Why does a bird-scaring electric wire or a heater coil glow red-hot, while household wiring does not?
Answer: A — The coil has high resistance and carries enough current to become very hot; ordinary wiring has low resistance
The heating element is a high-resistance wire designed to get hot (and glow) when current flows. Household copper wiring has low resistance and stays cool. Matching resistance to purpose is key in appliance design.
Q47. hard
An electromagnet loses its magnetism when the current is switched off because:
Answer: A — The magnetic effect exists only while current flows through the coil
An electromagnet is magnetic only while current flows. When the current stops, the magnetic field disappears and the soft-iron core loses its magnetism. This on/off control is the electromagnet's key feature.
Q49. hard
A wire carrying current is coiled into many loops (a solenoid). Compared to a single straight wire, the coil:
Answer: A — Produces a much stronger magnetic field
Winding the wire into many loops (a solenoid) adds up the magnetic effects of each loop, producing a much stronger, more uniform magnetic field - the basis of electromagnets and electric motors.
Q51. hard
The chemical effect of electric current was demonstrated by passing current through:
Answer: A — A conducting solution, where deposits or gas bubbles appeared at the electrodes
When current passes through a conducting solution (electrolyte), chemical changes occur - such as gas bubbles forming, metal being deposited, or colour changes at the electrodes. This is the chemical effect of current.
Q53. hard
Why is a THICK fuse wire or a wrong (very high rated) fuse dangerous?
Answer: A — It may not melt in time during a fault, so the wiring can overheat and catch fire
A fuse must be rated correctly. If the fuse is too thick or too high-rated, it will not melt when a dangerous current flows, so it fails to protect the circuit - the wiring can overheat and cause a fire.
Q55. hard
Which of these correctly explains why electroplating is useful?
Answer: A — It gives objects an attractive finish and protects them from rust/wear using only a thin layer of costly metal
Electroplating coats a cheaper metal with a thin layer of a better metal (chromium, gold, silver, tin, zinc). This improves appearance, resists corrosion and wear, and saves money since only a thin layer of the expensive metal is used.
Q59. hard
The magnetic effect of electric current forms the basis of which important machine?
Answer: A — The electric motor (used in fans, pumps, mixers)
The electric motor works on the magnetic effect of current - a current-carrying coil in a magnetic field experiences a force and rotates. Motors run fans, washing machines, pumps, mixers and countless machines.