MCAT® ExamChemical and Physical Foundations of Biological SystemsMedium
A medical instrument uses a small electromagnet. The current supplied to the coil of the electromagnet is doubled, while the number of turns in the coil and its length remain constant. What effect will this have on the magnetic field strength inside the electromagnet?
- AThe magnetic field strength will remain unchanged.
- BThe magnetic field strength will be quadrupled.
- CThe magnetic field strength will be halved.
- DThe magnetic field strength will be doubled.
Show answer & explanationAnswer & explanation
Correct answer: D. The magnetic field strength will be doubled.
The magnetic field strength (B) inside a solenoid (a common form of electromagnet) is directly proportional to the current (I) flowing through its coil. The formula for the magnetic field inside a long solenoid is B = μ₀nI, where μ₀ is the permeability of free space, n is the number of turns per unit length, and I is the current. If the current (I) is doubled, and n remains constant, then B will also double.
Why the other options are wrong
- A. The magnetic field strength is directly dependent on the current, so it will change.
- B. The magnetic field strength is linearly dependent on current, not quadratically.
- C. Doubling the current will increase, not halve, the magnetic field strength.
Magnetic Field of a Solenoid
The magnetic field inside a long solenoid is uniform and directly proportional to the current flowing through its coils and the number of turns per unit length.
- Formula: B = μ₀nI, where B is magnetic field strength, μ₀ is permeability of free space, n is number of turns per unit length, and I is current.
- The field lines inside a solenoid are approximately parallel and equally spaced.
- Increasing current increases magnetic field strength.
- Increasing the number of turns per unit length (n) increases magnetic field strength.
Memory trick: Current is the direct driver of solenoid's power!