CBSE Class 12 Physics Chapter 6: Electromagnetic Induction NCERT Solutions
This resource provides detailed NCERT Solutions for Class 12 Physics, Chapter 6 on Electromagnetic Induction. It covers essential concepts like Lenz's Law and the prediction of induced current directions in various scenarios involving magnets and coils. The solutions explain how to determine the direction of induced current when a magnet moves towards or away from a closed loop, and in situations where resistance in a circuit is changed. This chapter is crucial for understanding the fundamental principles of electromagnetism and its applications. These solutions are designed to help students grasp the concepts thoroughly and prepare effectively for their board examinations by offering clear, step-by-step explanations for each exercise problem.
Quick info
| Board | CBSE |
|---|---|
| Class | Class 12 |
| Subject | Physics |
| Session | 2026 |
| Language | English |
| Type | NCERT Solutions |
| Chapter | Chapter 6: Electromagnetic Induction - NCERT Exercises Solutions |
Chapter summary
This chapter focuses on Electromagnetic Induction, specifically addressing exercises related to predicting the direction of induced currents. It reinforces the understanding of Lenz's Law, which dictates that the induced current opposes the change in magnetic flux. The solutions cover scenarios involving the motion of magnets relative to conducting loops and changes in current within nearby circuits, helping students apply the principles of electromagnetic induction to solve practical problems.
Learning outcomes
- Understand the concept of induced current and its direction.
- Apply Lenz's Law to predict the direction of induced current.
- Analyze scenarios involving magnetic flux changes in closed loops.
- Determine induced current direction based on magnet's motion.
- Explain the effect of changing resistance on induced current.
Topics covered
Paper topics
- Electromagnetic Induction
- Lenz's Law
- Induced Current Direction
- Magnetic Flux
- Motion of Magnets
- Changes in Circuit Resistance
- Tapping Key
- Rheostat
Important topics
- Lenz's Law
- Predicting Induced Current Direction
- Magnet moving towards/away from a coil
- Effect of changing current in a circuit
PDF preview
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Questions and Solutions
Question 6.1
(a) A stationary coil and a bar magnet moving towards it with its North pole facing the coil.
(b) A stationary coil and a bar magnet moving away from it with its North pole facing the coil.
(c) A stationary coil and a bar magnet moving towards it with its South pole facing the coil.
(d) A stationary coil and a bar magnet moving away from it with its South pole facing the coil.
(e) A stationary coil and a bar magnet moving towards it with its North pole facing the coil, and the tapping key in the circuit connected to the magnet is just closed.
(f) A stationary coil and a bar magnet moving towards it with its North pole facing the coil, and the tapping key in the circuit connected to the magnet is just released.
(g) A stationary coil and a bar magnet moving towards it with its North pole facing the coil, and the rheostat setting is being changed to increase the resistance.
(h) A stationary coil and a bar magnet moving towards it with its North pole facing the coil, and the rheostat setting is being changed to decrease the resistance.
The direction of the induced current in a closed loop is governed by Lenz's Law. Lenz's Law states that the induced current will flow in a direction that opposes the change in magnetic flux causing it.
Let's analyze each situation:
- (a) North pole moving towards the coil: To oppose the incoming North pole, the face of the coil acts as a North pole. This requires the induced current to flow in a counter-clockwise direction when viewed from the magnet's side.
- (b) North pole moving away from the coil: To oppose the receding North pole, the face of the coil acts as a South pole. This requires the induced current to flow in a clockwise direction when viewed from the magnet's side.
- (c) South pole moving towards the coil: To oppose the incoming South pole, the face of the coil acts as a South pole. This requires the induced current to flow in a clockwise direction when viewed from the magnet's side.
- (d) South pole moving away from the coil: To oppose the receding South pole, the face of the coil acts as a North pole. This requires the induced current to flow in a counter-clockwise direction when viewed from the magnet's side.
- (e) Tapping key just closed: When the tapping key is closed, the current in the primary circuit (connected to the magnet) starts increasing. This increasing current produces an increasing magnetic field. To oppose this increase in magnetic flux, the induced current in the stationary coil will flow in a direction that creates a magnetic field opposing the primary field. If the primary circuit's North pole is moving towards the coil, the induced current will be counter-clockwise.
- (f) Tapping key just released: When the tapping key is released, the current in the primary circuit starts decreasing. This decreasing current produces a decreasing magnetic field. To oppose this decrease in magnetic flux, the induced current in the stationary coil will flow in a direction that creates a magnetic field in the same direction as the primary field. If the primary circuit's North pole is moving towards the coil, the induced current will be clockwise.
- (g) Rheostat setting changed (resistance increased): Increasing the resistance in the primary circuit causes the current to decrease. This leads to a decrease in magnetic flux. The induced current will oppose this decrease, flowing in a direction to strengthen the magnetic field.
- (h) Rheostat setting changed (resistance decreased): Decreasing the resistance in the primary circuit causes the current to increase. This leads to an increase in magnetic flux. The induced current will oppose this increase, flowing in a direction to weaken the magnetic field.
Note: The specific directions (e.g., along qrpq) mentioned in the source are not fully defined without the actual figures. The explanations above describe the general principles based on Lenz's Law for typical scenarios.
Common mistakes
- Confusing the direction of induced current with the direction of magnetic field lines.
- Incorrectly applying Lenz's Law to determine the opposition to flux change.
- Misinterpreting the effect of the tapping key's action (closing vs. releasing).
Revision tips
- Review Lenz's Law thoroughly before attempting the problems.
- Draw diagrams for each situation to visualize the magnetic field and flux changes.
- Practice predicting the induced current direction for various magnet-coil orientations.
- Pay close attention to the wording describing changes in the circuit (e.g., 'just closed', 'just released', 'decreasing rate').
Practice MCQs
Q1. According to Lenz's Law, the direction of the induced current in a closed loop is such that it:
Explanation: Lenz's Law states that the induced current flows in a direction that opposes the very change in magnetic flux that produced it.
Q2. When the North pole of a bar magnet is moved towards a closed coil, what is the direction of the induced current in the coil when viewed from the magnet's side?
Explanation: To oppose the incoming North pole, the face of the coil acts as a North pole, which requires a counter-clockwise current when viewed from the magnet's side.
Q3. If a tapping key is just released in a circuit connected to a coil, what happens to the magnetic flux through a nearby closed loop?
Explanation: Releasing the tapping key stops the current flow, causing the magnetic field and thus the magnetic flux through the nearby loop to decrease.
Q4. In which situation is no current induced in the closed loop?
Explanation: If the magnetic field lines are parallel to the plane of the loop, the magnetic flux through the loop is zero and does not change, hence no current is induced.
Q5. When the rheostat setting is changed, causing the current to decrease, the induced current in the nearby coil will:
Explanation: A decreasing current means decreasing magnetic flux. The induced current will oppose this decrease, thus flowing in a direction to create its own magnetic field in the same direction as the original field.
Frequently asked questions
What is the fundamental principle used to determine the direction of induced current in these NCERT solutions?
The fundamental principle used is Lenz's Law, which states that the direction of the induced current opposes the change in magnetic flux that produces it.
How does the motion of a magnet affect the induced current in a coil?
When a magnet moves towards or away from a coil, it changes the magnetic flux through the coil, inducing a current. The direction of this induced current opposes the motion of the magnet.
What happens when the tapping key is closed or released in a circuit near a coil?
Closing the tapping key increases the current and magnetic flux, inducing a current that opposes this increase. Releasing the key decreases the current and flux, inducing a current that opposes this decrease.
Does changing the resistance of a circuit affect induced current in a nearby coil?
Yes, changing the resistance alters the current in the primary circuit, which in turn changes the magnetic field and flux. This change in flux induces a current in the secondary coil.
When is no current induced in a closed loop, according to the solutions?
No current is induced when the magnetic field lines lie in the plane of the closed loop, as there is no change in magnetic flux through the loop in such a scenario.
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