CBSE Class 12 Physics (2026–27)
Chapter 6: Electromagnetic Induction
20 Important Questions and Answers
Electromagnetic Induction is an important chapter in Unit IV of the CBSE Class 12 Physics syllabus. Major topics include Faraday’s Laws, Lenz’s Law, induced EMF, self-induction, and mutual induction.
Q1. What is electromagnetic induction?
Answer:
Electromagnetic induction is the phenomenon of producing an electromotive force (EMF) or electric current in a conductor when the magnetic flux linked with it changes. This discovery was made by Faraday and Henry independently. A change in magnetic flux may occur by moving a magnet near a coil, moving the coil in a magnetic field, or changing the strength of the magnetic field. The induced current exists only as long as the magnetic flux changes. Electromagnetic induction forms the basic principle of generators, transformers, induction cookers, and many electrical devices. It demonstrates the close relationship between electricity and magnetism.
Q2. State Faraday’s First Law of Electromagnetic Induction.
Answer:
Faraday’s First Law states that whenever the magnetic flux linked with a closed circuit changes, an electromotive force is induced in the circuit. If the circuit is closed, an induced current also flows. The induced EMF exists only while the magnetic flux is changing. The change in flux may result from the relative motion between a magnet and a coil or due to a varying magnetic field. This law establishes the basic condition necessary for electromagnetic induction. It explains why no current is induced when a magnet remains stationary near a coil and why current appears when the magnet is moved.
Q3. State Faraday’s Second Law of Electromagnetic Induction.
Answer:
Faraday’s Second Law states that the magnitude of the induced EMF is directly proportional to the rate of change of magnetic flux linked with the circuit. Mathematically,
[E = -N\frac{d\Phi}{dt}]
where (E) is induced EMF, (N) is the number of turns, and (\Phi) is magnetic flux. The negative sign indicates the direction given by Lenz’s Law. A larger change in magnetic flux within a shorter time produces a greater induced EMF. This law is widely used in generators and transformers where changing magnetic fields continuously induce voltage in coils.
Q4. What is magnetic flux?
Answer:
Magnetic flux is the measure of the total magnetic field passing through a given surface. It indicates the number of magnetic field lines crossing the surface. Magnetic flux is represented by (\Phi) and is given by:
[\Phi = BA\cos\theta]
where (B) is magnetic field strength, (A) is area of the surface, and (\theta) is the angle between the magnetic field and the normal to the surface. Its SI unit is weber (Wb). Magnetic flux is maximum when the field is perpendicular to the surface and zero when the field is parallel to it. Changes in magnetic flux lead to electromagnetic induction.
Q5. What is Lenz’s Law?
Answer:
Lenz’s Law states that the direction of induced current is always such that it opposes the cause producing it. In other words, the induced current creates a magnetic field that opposes the change in magnetic flux responsible for its production. This law is represented by the negative sign in Faraday’s equation. Lenz’s Law is based on the principle of conservation of energy. Without this opposition, energy would be created without external work, which is impossible. The law helps determine the direction of induced current in coils and is important in understanding generators, transformers, and electromagnetic braking systems.
Q6. How does Lenz’s Law support the law of conservation of energy?
Answer:
Lenz’s Law ensures that the induced current opposes the change causing it. When a magnet is moved toward a coil, the induced current produces a magnetic field that repels the approaching magnet. Therefore, external work must be done to continue the motion. This work is converted into electrical energy in the coil. If the induced current aided the motion instead of opposing it, energy would be produced without any external work, violating the law of conservation of energy. Thus, Lenz’s Law guarantees that energy is neither created nor destroyed but only transformed from one form to another.
Q7. Define induced EMF.
Answer:
Induced electromotive force (EMF) is the voltage generated in a conductor whenever the magnetic flux linked with it changes. It is produced due to electromagnetic induction and is measured in volts. According to Faraday’s Law, induced EMF depends on the rate of change of magnetic flux. A faster change in flux results in a larger EMF. Induced EMF may be generated by moving a conductor in a magnetic field or by varying the magnetic field around a stationary conductor. Electrical generators operate on this principle and convert mechanical energy into electrical energy through induced EMF.
Q8. What is motional EMF?
Answer:
Motional EMF is the electromotive force induced in a conductor due to its motion through a magnetic field. When a conductor moves perpendicular to magnetic field lines, free electrons experience a magnetic force and accumulate at one end, creating a potential difference. The magnitude of motional EMF is:
[E = Blv]
where (B) is magnetic field strength, (l) is the length of the conductor, and (v) is its velocity. Motional EMF is the basic principle behind electric generators. It demonstrates how mechanical motion can be converted into electrical energy through electromagnetic induction.
Q9. What is self-induction?
Answer:
Self-induction is the phenomenon in which a changing current in a coil induces an EMF in the same coil. When current changes, the magnetic field produced by the coil also changes, causing a change in magnetic flux linked with the coil itself. This changing flux induces an EMF that opposes the change in current according to Lenz’s Law. The induced EMF is called back EMF. Self-induction is important in electrical circuits because it resists sudden changes in current. Devices such as inductors and choke coils work on the principle of self-induction.
Q10. Define coefficient of self-induction.
Answer:
The coefficient of self-induction, or inductance, is a measure of a coil’s ability to oppose changes in current through self-induced EMF. It is denoted by (L). Numerically, it is equal to the induced EMF produced when the rate of change of current is unity. Mathematically,
[E = -L\frac{dI}{dt}]
The SI unit of inductance is henry (H). A coil has an inductance of one henry if an EMF of one volt is induced when the current changes at the rate of one ampere per second. Greater inductance means greater opposition to current changes.
Q11. What is mutual induction?
Answer:
Mutual induction is the phenomenon in which a changing current in one coil induces an EMF in a nearby coil. The changing current in the first coil produces a changing magnetic field, which alters the magnetic flux linked with the second coil. As a result, an induced EMF appears in the second coil. This effect is the basis of transformers used in power transmission. Mutual induction depends on factors such as the number of turns, distance between coils, and magnetic properties of the core material. The greater the flux linkage, the greater the induced EMF.
Q12. Define coefficient of mutual induction.
Answer:
The coefficient of mutual induction (M) measures the effectiveness with which one coil induces EMF in another coil. It is defined as the induced EMF in one coil when the rate of change of current in the other coil is unity. Mathematically,
[E = -M\frac{dI}{dt}]
Its SI unit is henry (H). Mutual inductance depends on the number of turns in both coils, their orientation, distance between them, and the magnetic permeability of the medium. Transformers use high mutual inductance to efficiently transfer electrical energy between coils through changing magnetic fields.
Q13. What is an inductor?
Answer:
An inductor is an electrical component designed to store energy in the form of a magnetic field. It usually consists of a coil of insulated wire wound around an air core or magnetic core. When current flows through the coil, a magnetic field is produced around it. Due to self-induction, the inductor opposes changes in current. Inductors are widely used in electrical and electronic circuits for filtering signals, energy storage, tuning circuits, and reducing current fluctuations. Their effectiveness is measured by inductance, whose SI unit is henry.
Q14. Why is induced current produced only when magnetic flux changes?
Answer:
According to Faraday’s Laws, induced EMF depends on the rate of change of magnetic flux. If magnetic flux remains constant, there is no change in flux and therefore no induced EMF. Since current can flow only when an EMF exists, no induced current is produced under constant flux conditions. This explains why a stationary magnet near a coil does not induce current, while moving the magnet toward or away from the coil does. Thus, change in magnetic flux is the essential condition for electromagnetic induction.
Q15. What factors affect induced EMF?
Answer:
The magnitude of induced EMF depends on several factors. It increases with a greater rate of change of magnetic flux. Increasing the number of turns in a coil also increases induced EMF because more turns experience changing flux. Stronger magnetic fields produce larger flux changes and therefore larger EMF. Faster relative motion between a magnet and coil also increases induction. The orientation of the coil with respect to the magnetic field affects the effective flux linkage. Thus, induced EMF can be maximized by increasing flux change and reducing the time taken for the change.
Q16. What are eddy currents?
Answer:
Eddy currents are circulating currents induced in bulk metallic conductors when they are subjected to changing magnetic fields. These currents flow in closed loops within the conductor. Eddy currents produce heat due to electrical resistance and may lead to energy losses in transformers and motors. However, they also have useful applications. They are used in induction furnaces for heating metals, electromagnetic brakes, speedometers, and energy meters. To reduce unwanted eddy currents, transformer cores are laminated into thin insulated sheets. This increases resistance and minimizes energy loss.
Q17. Mention two applications of electromagnetic induction.
Answer:
Electromagnetic induction has numerous practical applications. One important application is the electric generator, which converts mechanical energy into electrical energy by inducing EMF in rotating coils. Another major application is the transformer, which transfers electrical energy between circuits and changes voltage levels using mutual induction. Electromagnetic induction is also used in induction cookers, metal detectors, wireless charging systems, microphones, and bicycle dynamos. These devices operate by utilizing changing magnetic fields to generate induced currents or voltages. Thus, electromagnetic induction plays a vital role in modern electrical technology.
Q18. Why is a galvanometer used in electromagnetic induction experiments?
Answer:
A galvanometer is a sensitive instrument used to detect small electric currents. In electromagnetic induction experiments, the induced current is often very small and may not be visible through other instruments. A galvanometer indicates the presence and direction of induced current by showing a deflection of its pointer. The direction of deflection helps determine the direction of induced current according to Lenz’s Law. It also confirms that current is induced only when magnetic flux changes. Therefore, the galvanometer is an essential device for studying electromagnetic induction phenomena experimentally.
Q19. What is the SI unit of magnetic flux? Define it.
Answer:
The SI unit of magnetic flux is the weber (Wb). One weber is defined as the magnetic flux that, when reduced uniformly to zero in one second through a single-turn coil, induces an EMF of one volt in the coil. Mathematically,
[1,Wb = 1,T \times 1,m^2]
where tesla (T) is the SI unit of magnetic field. Magnetic flux is an important quantity in electromagnetic induction because induced EMF depends directly on the rate of change of magnetic flux linked with a circuit.
Q20. Distinguish between self-induction and mutual induction.
Answer:
Self-induction occurs when a changing current in a coil induces EMF in the same coil. It opposes changes in current and produces back EMF. Mutual induction occurs when a changing current in one coil induces EMF in another nearby coil. Self-induction involves only one coil, whereas mutual induction requires two coils. Self-induction is used in inductors and choke coils, while mutual induction is the operating principle of transformers. Both phenomena are based on Faraday’s Laws and depend on changing magnetic flux, but they differ in the number of coils involved and their practical applications.