Case Study:

At a test track in Japan, a high-speed Maglev train was observed to accelerate beyond 500 km/h while maintaining a consistent gap of about 10 mm above the track. Unlike conventional trains, there was no physical contact between wheels and rails, yet the train remained stable even at high speeds. Engineers recorded that the train uses superconducting coils carrying currents up to 10⁵ A, while the track contains conducting loops arranged periodically.

As the train moves, these coils generate a strong magnetic field. Due to relative motion, currents are induced in the track loops, producing their own magnetic fields. The interaction between the magnetic field of the train and the induced currents results in forces that both lift and stabilize the train.

According to NCERT principles from Moving Charges and Magnetism, a current-carrying conductor placed in a magnetic field experiences a force given by the Lorentz force. The direction of this force depends on the direction of current and magnetic field.

Engineers must carefully control current magnitude and direction to ensure that the upward magnetic force balances the gravitational force on the train, preventing instability or contact with the track.

While Maglevs are a pinnacle of engineering, you can see similar principles in Magnetism in Daily Life: From Speakers to MRI Machines.

CASE-BASED QUESTIONS

MCQ

Q1. The primary reason the Maglev train floats above the track is:
A. Electrostatic force between train and track
B. Gravitational force reduction at high speed
C. Magnetic force due to interaction of currents and magnetic field
D. Frictional force cancellation

Q2. If the direction of current in the superconducting coils is reversed, the magnetic force will:
A. Remain unchanged
B. Reverse direction
C. Become zero
D. Double in magnitude

Assertion - Reason

Q3. (A): Maglev trains require continuous energy input to maintain levitation.
Reason (R): Magnetic force depends on current flowing in the conductors.

A. Both A and R are true, and R is the correct explanation
B. Both A and R are true, but R is not the correct explanation
C. A is true, R is false
D. A is false, R is true

Application-Based

Q4. If the speed of the Maglev train increases, the induced current in the track loops increases. Explain how this affects the lifting force on the train.

Application-Based

Q5. Why is precise control of current necessary to maintain a constant gap between the train and track?

Data/Logic-Based (Advanced)

Q6. A Maglev train of mass 2 × 10⁵ kg is levitating steadily. If the gravitational force is balanced by magnetic force, calculate the required magnetic force. (g = 9.8 m/s²)

3. ANSWER KEY WITH EXPLANATION

A1. C- Maglev works on magnetic interaction between current-carrying coils and induced currents, producing Lorentz force (NCERT principle).

A2. B- Force on a current-carrying conductor reverses when current direction changes (Fleming’s Left-Hand Rule).

To better visualize the direction of these forces, check out our guide on the Right Hand Rule Explained with Easy Diagrams.

A3. A- Levitation depends on current; without current, magnetic force disappears. Hence continuous energy is needed.

A4. Higher speed → greater induced current → stronger magnetic field → increased lifting force (as per electromagnetic induction and Lorentz force).

A5. Magnetic force must exactly balance weight. Any variation in current changes force, causing instability or contact with track.

A6. F = mg = (2 × 10⁵) × 9.8 = 1.96 × 10⁶ N
Magnetic force equals weight for stable levitation.

Preparing for your CBSE boards? Download our Class 12 Physics Unsolved Practice Papers for more exam-style practice.

Mastered this case study? Test your knowledge with these Top 20 Important Questions from Magnetic Force on Charges.

HOTS EXTENSION QUESTIONS

1. If the Maglev train enters a region where the magnetic field strength suddenly decreases, predict the effect on levitation and justify your answer.

2. Suggest how engineers can modify the system to maintain stable levitation at very low speeds where induced currents are weak.

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