Case Study:

Fourteen-year-old Raghav was surprised when doctors told his uncle that an MRI scan could detect problems inside the body without any surgery or harmful cuts. During the hospital visit, he noticed warning boards outside the MRI room saying: “Strong Magnetic Field Area - Metal Objects Not Allowed.” He wondered how a machine inside a hospital could produce such a powerful magnetic field.

An MRI (Magnetic Resonance Imaging) machine contains large coils of wire arranged in the form of long cylindrical solenoids. When electric current passes through these coils, they behave like very powerful electromagnets.

If you’re wondering exactly how that flow of electrons begins, you can refresh your basics on what electric current is and how charges flow before diving deeper into magnetism.

The magnetic field produced inside the MRI machine can be nearly 30,000 times stronger than Earth’s magnetic field. This strong field helps doctors obtain detailed images of organs, muscles, and bones.

Engineers observed that increasing the number of turns in the solenoid or increasing the electric current made the magnetic field stronger.

This relationship between current and the strength of the field is rooted in Ohm’s Law, which explains how voltage and resistance dictate the current flowing through these massive coils

However, if the current became too high, the coils heated up rapidly due to the heating effect of electric current. To reduce overheating, many MRI machines use cooling systems with liquid helium.

Beyond cooling, safety is paramount when dealing with such high energy. It's fascinating to see how electric fuses and circuit breakers act as the ultimate bodyguards for sensitive medical equipment.

During a test, two MRI coils were compared:

In complex machines like an MRI, how these coils are wired matters - check out the differences between series and parallel circuits to see why one configuration is often better than the other for heavy machinery.

Doctors noticed that Coil B produced a much stronger magnetic field and clearer scan images.
This investigation helped students understand how electricity and magnetism are closely connected through the principle of electromagnetism.

While an MRI uses an incredible amount of power, the same principles apply to your electricity bill at home. You can learn more about electrical power and energy consumption here.

CASE-BASED QUESTIONS

 MCQs 

Q1. Why does the MRI coil behave like a magnet when current flows through it?
A. Due to chemical reaction in the wire
B. Due to magnetic effect of electric current
C. Due to Earth’s magnetic field
D. Due to friction between coils

Q2. Which change would most likely increase the strength of the magnetic field inside the MRI machine?
A. Decreasing current in the coil
B. Reducing number of turns in the solenoid
C. Increasing the number of turns in the coil
D. Using thinner wires only

 Assertion–Reason 

Q3. Assertion (A): A solenoid carrying current behaves like a bar magnet.
Reason (R): Magnetic field lines inside a current-carrying solenoid are nearly parallel and uniform.
A. Both A and R are true, and R is the correct explanation of A
B. Both A and R are true, but R is not the correct explanation of A
C. A is true, but R is false
D. A is false, but R is true

 Application-Based 

Q4. Why are metal objects strictly prohibited near MRI machines?

Q5. An engineer wants to make the MRI magnetic field stronger without changing the coil length. Suggest two possible methods based on electromagnetism.

 Data/Logic-Based 

Q6. Coil A has 800 turns and Coil B has 1600 turns. Both carry the same current of 2 A.
(i) Which coil produces the stronger magnetic field?
(ii) Explain the reason using the concept of solenoids.

 Competency - Based 

Q7. MRI machines use cooling systems because the coils become hot during operation. Which NCERT concept explains this heating?
A. Chemical effect of current
B. Heating effect of electric current
C. Magnetic induction only
D. Reflection of light\

ANSWER KEY WITH EXPLANATION 

A1: B. Due to magnetic effect of electric current
Explanation:  According to NCERT, a current-carrying conductor produces a magnetic field around it. Therefore, the MRI coil acts like an electromagnet.

A2: C. Increasing the number of turns in the coil
Explanation:  The magnetic field inside a solenoid becomes stronger when the number of turns increases. More turns produce a stronger combined magnetic field.

A3: A. Both A and R are true, and R is the correct explanation of A
Explanation:  A current-carrying solenoid behaves like a bar magnet because it produces a strong and nearly uniform magnetic field inside it.

A4: Metal objects are attracted strongly toward the MRI machine because it produces a very powerful magnetic field. This can cause accidents or damage equipment.

A5: Increase the number of turns in the solenoid
Increase the electric current through the coil
Explanation:  According to NCERT, the strength of an electromagnet depends mainly on current and the number of turns of the coil.

A6: (i) Coil B produces the stronger magnetic field.
(ii) Coil B has more turns, so the magnetic effects of each turn combine to create a stronger field.
Explanation:  The strength of a solenoid increases with the number of turns for the same current.

A7: B. Heating effect of electric current
Explanation:  When current flows through the MRI coils, electrical energy converts into heat energy due to resistance in the wire.

HOTS EXTENSION QUESTIONS

Q1. If engineers double the current in an MRI coil, what problems might arise apart from stronger magnetism? Explain scientifically.

Q2. Suppose an MRI machine is redesigned using fewer coil turns but thicker wire. Predict how this may affect magnetic strength and heating of the system.

Still have a lingering question about solenoids? Post your doubt on our Discuss Forum to get help from experts, or try a quick Physics Quiz to see how much you’ve retained!

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