CBSE Class 10 Science (2026–27)
Chapter 12: Magnetic Effects of Electric Current
20 Important Questions and Answers
Q1. What is the magnetic effect of electric current?
Answer:
The magnetic effect of electric current is the phenomenon in which an electric current flowing through a conductor produces a magnetic field around it. This discovery was made by Hans Christian Oersted in 1820. When current passes through a wire, magnetic field lines are formed around the conductor in concentric circles. The strength of the magnetic field depends on the amount of current flowing through the conductor and the distance from it. This principle is used in many electrical devices such as electric motors, generators, loudspeakers, and electromagnets. The magnetic effect establishes an important relationship between electricity and magnetism.
Q2. State the Right-Hand Thumb Rule.
Answer:
The Right-Hand Thumb Rule helps determine the direction of the magnetic field around a straight current-carrying conductor. According to this rule, if we hold the conductor in our right hand with the thumb pointing in the direction of current, then the curled fingers indicate the direction of the magnetic field lines around the conductor. The magnetic field forms concentric circles around the wire. This rule is useful for understanding the relationship between current direction and magnetic field direction. It is widely used in electromagnetism and helps in solving problems related to magnetic fields produced by electric currents.
Q3. Describe the magnetic field around a straight current-carrying conductor.
Answer:
A straight current-carrying conductor produces a magnetic field around it. The magnetic field lines form concentric circles centered on the conductor. The direction of these field lines can be determined using the Right-Hand Thumb Rule. The magnetic field is strongest near the conductor and becomes weaker as the distance from the conductor increases. If the current is increased, the magnetic field strength also increases. The pattern of magnetic field lines can be observed using iron filings or a compass placed around the conductor. This phenomenon demonstrates the magnetic effect of electric current and forms the basis of many electromagnetic devices.
Q4. How does the magnetic field of a circular current-carrying loop differ from that of a straight conductor?
Answer:
In a circular current-carrying loop, the magnetic field lines produced by different parts of the loop combine at the center, making the magnetic field stronger than that of a straight conductor. The field lines around the loop are circular near the wire but become nearly parallel at the center. The magnetic field strength increases with the number of turns in the loop and the amount of current flowing through it. The direction of the magnetic field can be determined using the Right-Hand Rule. Circular loops are used in electromagnets and electric motors because they produce a stronger and more concentrated magnetic field.
Q5. What is an electromagnet? Mention two uses.
Answer:
An electromagnet is a temporary magnet produced by passing electric current through a coil wound around a soft iron core. When current flows, the iron core becomes magnetized and behaves like a strong magnet. When the current is switched off, the magnetism disappears. The strength of an electromagnet depends on the number of turns in the coil and the amount of current flowing through it. Electromagnets are widely used because their magnetic strength can be controlled. Two common uses are in electric bells and cranes used for lifting heavy iron scrap in factories and recycling plants.
Q6. What is a solenoid? Why is it important?
Answer:
A solenoid is a long cylindrical coil made by winding insulated copper wire closely in the form of a helix. When electric current passes through the solenoid, it produces a magnetic field similar to that of a bar magnet. The magnetic field inside the solenoid is strong and nearly uniform. The strength of the field increases with the number of turns and the current flowing through it. Solenoids are important because they are used to make electromagnets, electric relays, magnetic locks, and various electronic devices. They help convert electrical energy into magnetic energy efficiently.
Q7. What is Fleming’s Left-Hand Rule?
Answer:
Fleming’s Left-Hand Rule is used to determine the direction of force acting on a current-carrying conductor placed in a magnetic field. Stretch the thumb, forefinger, and middle finger of the left hand so that they are mutually perpendicular. If the forefinger points in the direction of the magnetic field and the middle finger points in the direction of current, then the thumb indicates the direction of the force or motion of the conductor. This rule is important in understanding the working of electric motors, where electrical energy is converted into mechanical energy.
Q8. Why does a current-carrying conductor experience a force in a magnetic field?
Answer:
A current-carrying conductor experiences a force when placed in a magnetic field because the magnetic field produced by the current interacts with the external magnetic field. This interaction creates a force on the conductor. The direction of this force depends on the direction of the current and the magnetic field and can be determined using Fleming’s Left-Hand Rule. If either the current or magnetic field direction is reversed, the force direction also reverses. This principle forms the basis of electric motors, where conductors move under the influence of magnetic forces and produce mechanical motion.
Q9. Explain the construction of an electric motor.
Answer:
An electric motor consists of a rectangular coil placed between the poles of a strong magnet. The coil is connected to a split-ring commutator and carbon brushes. The coil can rotate freely around an axle. When electric current flows through the coil, magnetic forces act on its sides, causing it to rotate. The split-ring commutator reverses the direction of current after every half rotation, ensuring continuous rotation in the same direction. Electric motors convert electrical energy into mechanical energy. They are widely used in fans, mixers, washing machines, water pumps, and many industrial machines.
Q10. What is the function of a split-ring commutator in an electric motor?
Answer:
The split-ring commutator is an essential component of an electric motor. It consists of two halves of a metallic ring connected to the ends of the coil. Its main function is to reverse the direction of current in the coil after every half rotation. This reversal changes the direction of the magnetic force acting on the coil, allowing it to continue rotating in the same direction. Without the commutator, the coil would stop after half a turn. Thus, the split-ring commutator ensures continuous rotation and smooth operation of the electric motor.
Q11. What is electromagnetic induction?
Answer:
Electromagnetic induction is the process of producing electric current in a conductor by changing the magnetic field around it. This phenomenon was discovered by Michael Faraday. When a magnet is moved towards or away from a coil, or when the magnetic field linked with the coil changes, an induced current is produced. The induced current exists only while the magnetic field is changing. This principle is the basis of electric generators, transformers, and many electrical devices. Electromagnetic induction demonstrates the conversion of mechanical energy into electrical energy.
Q12. State Fleming’s Right-Hand Rule.
Answer:
Fleming’s Right-Hand Rule helps determine the direction of induced current in a conductor moving in a magnetic field. Stretch the thumb, forefinger, and middle finger of the right hand so that they are mutually perpendicular. If the forefinger points in the direction of the magnetic field and the thumb points in the direction of motion of the conductor, then the middle finger gives the direction of the induced current. This rule is widely used in understanding the working of electric generators. It helps explain how mechanical motion can generate electrical energy through electromagnetic induction.
Q13. Explain the working principle of an electric generator.
Answer:
An electric generator works on the principle of electromagnetic induction. It converts mechanical energy into electrical energy. In a generator, a coil is rotated between the poles of a strong magnet. As the coil rotates, the magnetic field linked with it changes continuously. This change induces an electric current in the coil. The direction of induced current can be determined using Fleming’s Right-Hand Rule. The generated current is collected through brushes and rings. Electric generators are used in power stations to produce electricity from various energy sources such as water, wind, steam, and nuclear energy.
Q14. Differentiate between an electric motor and an electric generator.
Answer:
An electric motor converts electrical energy into mechanical energy, while an electric generator converts mechanical energy into electrical energy. A motor works on the principle that a current-carrying conductor experiences a force in a magnetic field. In contrast, a generator works on the principle of electromagnetic induction. Fleming’s Left-Hand Rule is used for motors, whereas Fleming’s Right-Hand Rule is used for generators. Motors are used in fans, mixers, and pumps, while generators are used in power stations to produce electricity. Thus, both devices perform opposite functions but involve magnetic effects of electric current.
Q15. What is the role of carbon brushes in electric machines?
Answer:
Carbon brushes are used in electric motors and generators to maintain electrical contact between stationary and rotating parts. They are made of carbon because carbon is a good conductor and experiences less wear due to friction. In a motor, carbon brushes supply current from the external circuit to the rotating coil through the commutator. In a generator, they collect the induced current from the rotating coil and transfer it to the external circuit. Carbon brushes ensure smooth transfer of current and efficient operation of the machine while minimizing damage to moving components.
Q16. What is the domestic electric fuse? Why is it used?
Answer:
A fuse is a safety device used in electrical circuits to protect appliances and wiring from excessive current. It consists of a thin wire made of a material with a low melting point. When current exceeds the safe limit due to overloading or short circuiting, the fuse wire melts and breaks the circuit. This stops the flow of current and prevents damage to electrical devices and fire hazards. Fuses are commonly installed in household circuits and electrical equipment. They provide a simple and effective method of electrical protection and ensure safe use of electricity.
Q17. What is overloading in an electric circuit?
Answer:
Overloading occurs when the current flowing through an electrical circuit exceeds its safe carrying capacity. This may happen when too many electrical appliances are connected to the same circuit or when high-power devices operate simultaneously. Excessive current causes heating of wires, which can damage insulation and increase the risk of fire. Overloading is prevented by using proper wiring, suitable fuse ratings, and circuit breakers. Electrical safety devices automatically disconnect the circuit when current becomes dangerously high. Thus, preventing overloading is essential for protecting electrical appliances and ensuring household safety.
Q18. What is short-circuiting? How can it be prevented?
Answer:
Short-circuiting occurs when the live wire and neutral wire come into direct contact due to damaged insulation or faulty wiring. This creates a path of very low resistance, causing a sudden flow of large current. The excessive current generates heat, which may damage appliances and cause fires. Short-circuiting can be prevented by maintaining good insulation, using quality electrical wiring, avoiding damaged cords, and installing fuses or miniature circuit breakers (MCBs). Regular inspection of electrical systems also helps prevent short circuits. Proper safety measures ensure safe and efficient use of electricity.
Q19. What is the function of an Earth wire?
Answer:
The Earth wire is a safety wire used in electrical appliances with metallic bodies. It connects the metal casing of the appliance directly to the ground. In case of insulation failure, any leakage current flows safely into the earth instead of passing through the user’s body. This prevents electric shocks and ensures safety. The Earth wire is usually covered with green insulation. It works along with fuses and circuit breakers to provide effective electrical protection. Earthing is an important safety measure in homes, offices, factories, and public buildings.
Q20. Why are magnetic field lines important?
Answer:
Magnetic field lines are imaginary lines used to represent the magnetic field around a magnet or current-carrying conductor. They help us understand the direction and strength of the magnetic field. The direction of the field is indicated by the tangent drawn to the field line at any point. The closeness of field lines shows the strength of the magnetic field; closer lines indicate a stronger field. Magnetic field lines never intersect each other because the magnetic field at a point can have only one direction. These lines are useful in studying electromagnetism and designing electrical devices.