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Q1. A miniature circuit breaker (MCB) is a device that:
An MCB is a safety device that automatically switches off (trips) when the current exceeds a safe limit. This protects the circuit from damage due to overcurrent or short circuits. It does not increase voltage, store electricity, or convert AC to DC. Unlike a fuse, it can be reset after tripping.
Q2. Which of the following is an advantage of an MCB over a fuse?
The main advantage of an MCB over a fuse is that it can be reused after tripping—you just need to reset it. A fuse, once blown, must be replaced. MCBs are not necessarily cheaper, they do not allow unlimited current (they are designed to trip at a rated value), and they do work on heating/magnetic effects.
Q3. The magnetic effect of electric current was first discovered by:
Hans Christian Oersted discovered the magnetic effect of electric current in 1820. He observed that a compass needle deflected when placed near a current-carrying wire. This was the first connection between electricity and magnetism. Thomas Edison invented the light bulb, Newton studied mechanics, and Einstein developed relativity.
Q4. When a compass needle is placed near a current-carrying straight wire, it:
A compass needle normally points in the north-south direction due to Earth’s magnetic field. When placed near a current-carrying wire, the magnetic field produced by the current causes the needle to deflect from its original position. It does not point towards the wire, stay still, or spin continuously.
Q5. The magnetic field produced by a straight current-carrying wire is:
The magnetic field around a straight current-carrying wire consists of concentric circular lines centered on the wire. The direction of the field is given by the right-hand thumb rule. It is not in the same direction as the wire, not straight lines coming out, and it is present when current flows.
Q6. What is a solenoid?
A solenoid is a coil of many circular turns of insulated copper wire wound in the shape of a cylinder. When current flows through it, it produces a magnetic field similar to that of a bar magnet. It is not a straight wire, a battery, or a measuring device.
Q7. The magnetic field inside a long solenoid is:
Inside a long solenoid, the magnetic field is strong and uniform (parallel lines, same strength at all points). This is one of the key properties of a solenoid. Outside the solenoid, the field is weak and spreads out. The field inside is not zero, weak, or only circular around each turn.
Q8. An electromagnet is a:
An electromagnet is a temporary magnet that produces a magnetic field only when electric current flows through its coil. It loses its magnetism when the current is switched off. It is not made of steel (which would retain magnetism), not natural, and does not keep its magnetism permanently.
Q9. Which core material is best suited for making a strong electromagnet?
Soft iron is the best core material for an electromagnet because it is easily magnetised and demagnetised. It produces a strong magnetic field when current flows and loses its magnetism almost completely when the current stops. Steel would retain magnetism (become a permanent magnet), while wood and plastic are non-magnetic.
Q10. The strength of an electromagnet can be increased by:
The strength of an electromagnet depends on the number of turns in the coil and the current flowing through it. Increasing either of these increases the magnetic field strength. Decreasing turns, using a wooden core, or switching off the current would decrease or eliminate the magnetism.
Q11. An electric bell works on the principle of:
An electric bell works on the magnetic effect of electric current. It uses an electromagnet to attract a metal armature, which strikes the bell. This cycle repeats due to the making and breaking of the circuit. The heating, chemical, and lighting effects are not involved in the working of an electric bell.
Q12. In an electric bell, what causes the hammer to strike the bell repeatedly?
In an electric bell, the hammer strikes repeatedly because the electromagnet attracts the armature, which breaks the circuit, causing the electromagnet to turn off. The armature returns, the circuit is completed again, and the cycle repeats. This continuous make-and-break action causes the hammer to strike the bell repeatedly.
Q13. A relay is a device that:
A relay is an electromagnetic switch that uses a small current to control a large current circuit. It is used to safely control high-power devices with low-power signals. It does not produce electricity, measure current, or store charge.
Q14. Which of the following devices uses an electromagnet to convert electrical energy into mechanical energy (movement)?
An electric motor uses an electromagnet to convert electrical energy into mechanical energy (rotational motion). It works on the principle that a current-carrying coil experiences a force in a magnetic field. A fuse uses heating, a heater uses heating, and an LED uses light emission.
Q15. A loudspeaker converts:
A loudspeaker converts electrical energy into sound energy. The varying current in the coil interacts with a permanent magnet, causing the cone to vibrate and produce sound. A microphone does the opposite (sound to electrical), and the other options are incorrect.
Q16. What is the main difference between a permanent magnet and an electromagnet?
The main difference is that an electromagnet can be switched on and off by controlling the current, while a permanent magnet always has magnetism. Permanent magnets are not necessarily stronger, they are not made of soft iron (soft iron is used for electromagnets), and electromagnets lose magnetism when the current stops.
Q17. Which of the following is NOT a way to increase the strength of an electromagnet?
Using a thicker wire without changing the number of turns does not increase the magnetic field strength; it reduces resistance but the number of turns and current are the main factors. Increasing turns, increasing current, and using a soft iron core all increase the strength. Thicker wire alone does not increase the field.
Q18. In an electric motor, the rotating part is called the:
The rotating part of an electric motor is called the rotor or armature. The stator is the stationary part, the commutator reverses current direction, and the brushes make contact with the commutator. The rotor/armature is the part that turns due to the magnetic forces.
Q19. An electric buzzer works on the same principle as an electric bell but:
A buzzer works on the same principle as a bell (using an electromagnet), but instead of a hammer striking a bell, it produces sound through a vibrating membrane or diaphragm. It still uses an electromagnet and does not produce light or use a heating element.
Q20. A coil of wire carrying current behaves like:
A coil of wire carrying current behaves like a bar magnet, with its own north and south poles. This is the principle behind electromagnets and solenoids. It does not behave like a resistor, capacitor, or battery. The magnetic field is produced due to the current flowing through the coil.
Q21. Which of the following devices uses an electromagnet to lift heavy iron scrap?
An electromagnetic crane uses a large electromagnet to lift heavy iron and steel scrap. The electromagnet is switched on to pick up the scrap and switched off to release it. An electric motor produces motion, a bell produces sound, and a loudspeaker produces sound.
Q22. When the direction of current in a solenoid is reversed, the magnetic poles:
The magnetic poles of a solenoid depend on the direction of current. If the current direction is reversed, the north and south poles of the solenoid also reverse. This is because the magnetic field direction is determined by the current direction. The poles do not remain the same or disappear; they simply swap.
Q23. The right-hand thumb rule is used to find:
The right-hand thumb rule is used to find the direction of the magnetic field around a current-carrying wire. If you point your thumb in the direction of the current, your fingers curl in the direction of the magnetic field. It does not find the direction of current itself, strength, or resistance.
Q24. What happens when a bar magnet is brought near a current-carrying solenoid?
A current-carrying solenoid behaves like a bar magnet with north and south poles. When a bar magnet is brought near it, they may attract or repel depending on which poles face each other. Like poles repel and unlike poles attract. So the interaction depends on the polarity.
Q25. Which of the following is a use of an electromagnet in a telephone?
In a telephone receiver, an electromagnet is used to convert electrical signals back into sound. The varying current causes the electromagnet to attract a diaphragm, which vibrates and produces sound. The microphone converts sound to electrical signals, and the other options are not related to electromagnets in telephones.
Q26. An electric current flowing through a wire produces:
An electric current flowing through a wire produces a magnetic field around it (the magnetic effect of current). This was discovered by Oersted. While heat and light may also be produced in some cases, the magnetic effect is the specific property that results directly from the current. Sound is not produced directly.
Q27. In a relay, the electromagnet is used to:
In a relay, the electromagnet is used to open or close a switch mechanically. When current flows through the electromagnet, it attracts an armature, which moves a set of contacts, opening or closing the circuit. It does not generate electricity, measure current, or produce heat.
Q28. The strength of the magnetic field produced by a solenoid depends on which of the following factors?
The strength of the magnetic field of a solenoid depends on the number of turns in the coil and the current flowing through it. Increasing either factor increases the magnetic field strength. The colour of the wire has no effect.
Q29. Which device uses an electromagnet to produce a warning sound?
An electric bell uses an electromagnet to produce a ringing sound, often used as a warning or alert. A heater produces heat, a bulb produces light, and a fan produces air movement. The bell is the correct answer for a warning sound.
Q30. What is the function of a commutator in an electric motor?
The commutator is a split ring that reverses the direction of current in the coil every half rotation. This ensures that the torque on the coil always acts in the same direction, allowing continuous rotation. It does not increase speed, keep the coil cool, or hold it in place.
Q31. An electromagnet loses its magnetism when:
An electromagnet loses its magnetism when the current is switched off. It is a temporary magnet that works only when current flows. Increasing current or number of turns would strengthen it, and using a soft iron core helps it work. The magnetism disappears when the current stops.
Q32. Which of the following statements about a solenoid is correct?
Inside a long solenoid, the magnetic field is uniform (same at all points) and strong. Outside the solenoid, the field is weak and spreads out. The field is not zero, and the field outside is weaker than inside. A solenoid does produce a magnetic field.
Q33. The device that uses an electromagnet to convert electrical energy into sound energy in a telephone receiver is essentially a:
A loudspeaker uses an electromagnet to convert electrical energy into sound energy. The varying current in the coil interacts with a permanent magnet, causing the cone to vibrate and produce sound. A microphone does the opposite (sound to electrical), and the other options are different devices.
Q34. An electric current is passed through a solenoid. A compass needle placed near one end of the solenoid points towards the solenoid. If the current direction is reversed, the compass needle will:
When the current is reversed, the polarity of the solenoid reverses. If the compass needle initially pointed towards the solenoid (attracted to the south pole), reversing the current would make that end a north pole, so the needle would point away (repel). The needle would not stay still, point towards again, or spin.
Q35. Which of the following is an advantage of using an MCB over a rewirable fuse?
The main advantage of an MCB is that it can be reset after tripping, while a rewirable fuse must be replaced once blown. MCBs are faster to respond, not more expensive to maintain, and they do protect against short circuits. The reset feature makes them more convenient.
Q36. In an electric bell, the soft iron armature is attracted by the electromagnet. What happens immediately after the armature is attracted?
In an electric bell, when the armature is attracted to the electromagnet, it moves and breaks the circuit at the contact screw. This turns off the electromagnet, allowing the armature to return. The circuit is then completed again, and the cycle repeats. The circuit does not stay permanently complete, current does not increase sharply, and the bell continues ringing.
Q37. Which of the following materials is most suitable for making the core of an electromagnet that needs to be switched on and off frequently?
Soft iron is most suitable because it is easily magnetised and demagnetised, allowing the electromagnet to be switched on and off quickly. Steel would retain magnetism (become a permanent magnet), and cobalt and nickel are not as suitable for frequent switching. Soft iron is the standard material for electromagnet cores.
Q38. A current-carrying coil of wire is suspended freely. It will align itself:
A freely suspended current-carrying coil behaves like a magnet and aligns itself along the Earth’s north-south direction, similar to a compass needle. This is because the Earth’s magnetic field exerts a torque on the coil. It does not align randomly, perpendicular, or east-west.
Q39. Which part of an electric motor ensures that the coil continues to rotate in the same direction?
The commutator ensures that the coil continues to rotate in the same direction by reversing the current direction every half turn. This keeps the torque acting in the same direction. The battery provides current, the magnets provide the field, and wires connect the circuit. The commutator is responsible for the continuous rotation.
Q40. An electromagnetic relay is commonly used in:
Electromagnetic relays are commonly used in car ignition systems and industrial control panels to control large currents with small signals. They are not used in electric fans, bulbs, or heaters as their primary function. Relays are essential for automation and safety.
Q41. What happens to a compass needle placed near a current-carrying wire if the current is increased?
Increasing the current increases the strength of the magnetic field around the wire. This causes the compass needle to experience a stronger force, resulting in a greater deflection from its original north-south position. The needle does not decrease its deflection, stop, or spin.
Q42. The device that uses an electromagnet to separate magnetic materials from non-magnetic materials is called a:
A magnetic separator uses an electromagnet to attract and separate magnetic materials (like iron) from non-magnetic materials. It is used in industries to separate metal scraps. An electric motor, loudspeaker, and relay have different functions. The magnetic separator is the correct device for this purpose.
Q43. In a loudspeaker, the cone vibrates because:
In a loudspeaker, the varying current in the coil produces a varying magnetic field. This field interacts with the field of a permanent magnet, causing the coil and attached cone to move back and forth, producing sound waves. The cone is not made of magnetic material, the current is not constant, and it is not heated.
Q44. An MCB trips when the current exceeds its rated value because:
An MCB trips when excessive current heats a bimetallic strip (or activates an electromagnet), causing it to bend and open the circuit. It does not melt a wire (like a fuse), the voltage does not drop to zero, and it is not turned off manually. The bimetallic strip is the key component.
Q45. Which of the following is NOT a use of an electromagnet?
Electromagnets are used for lifting heavy iron, in electric bells, and in relays. They are NOT used for making permanent bar magnets—permanent magnets are made from materials like steel that retain magnetism. Electromagnets are temporary magnets; they are not suitable for making permanent magnets.
Q46. In an electric bell, the role of the spring (or springy armature) is to:
In an electric bell, the spring (or springy armature) pushes the armature back to its original position when the electromagnet turns off. This breaks the circuit and allows the cycle to repeat, causing the hammer to strike the bell repeatedly. It does not increase volume, conduct electricity, or hold the electromagnet.
Q47. A solenoid with a soft iron core is called an electromagnet. If we replace the soft iron core with a steel rod, the device will:
Steel retains magnetism (it has high retentivity). If the soft iron core is replaced with steel, the device will become a permanent magnet after the current is switched off. It will not be a stronger electromagnet, stop producing a field, or work the same. Steel is not used for electromagnets that need to be switched off.
Q48. The magnetic field produced by a current-carrying solenoid is stronger than that produced by a straight wire because:
In a solenoid, the magnetic fields produced by each turn of the coil combine (add up) inside the solenoid, resulting in a stronger overall field. This is why a solenoid produces a much stronger magnetic field than a straight wire with the same current. Voltage, wire thickness, and resistance are not the primary reasons.
Q49. A buzzer is similar to an electric bell but does not have a:
A buzzer is similar to an electric bell in that it uses an electromagnet and a vibrating mechanism, but it does not have a hammer and gong (bell). Instead, it produces sound through a vibrating diaphragm or membrane. It still uses an electromagnet, a battery, and a spring-like mechanism.
Q50. When you press the switch of an electric bell, the circuit is completed. What sequence of events follows?
The correct sequence is: the electromagnet attracts the armature, which breaks the circuit, turning off the electromagnet. The armature returns due to the spring, completing the circuit again, and the cycle repeats. This continuous cycle makes the bell ring repeatedly. The other sequences are incorrect or describe a single strike.