Force On A Current-carrying Conductor
A straight wire of length 0.4 m carries a current of 5 A and lies perpendicular to a uniform magnetic field of 0.6 T; calculate the force acting on this wire.
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Solution
1.2 N
From NCERT Class 12, Chapter 4 (Moving Charges and Magnetism), a straight conductor of length L carrying current I in a magnetic field B experiences a force F=BILsinθ, where θ is the angle between the current direction and the field. This macroscopic force is the collective effect of the Lorentz force on all the moving charges inside the wire. Since the wire is perpendicular to the field, θ=90∘ and sinθ=1. Substituting B=0.6 T, I=5 A, L=0.4 m: F=(0.6)(5)(0.4)=1.2 N. The value 0.6 N halves the answer, as if L=0.2 m. The value 12 N is ten times too large from a decimal-point error. The value 0.12 N is ten times too small for the same reason. Plausibility check: the units combine as T⋅A⋅m=N, and a force of about a newton on a short current-carrying wire in a strong field is entirely reasonable.
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About This Question
- Subject
- physics
- Chapter
- magnetic effects of current and magnetism
- Topic
- force on a current-carrying conductor
- Difficulty
- Easy
- Year
- 2025
Solution
Correct Answer:
1.2 N
From NCERT Class 12, Chapter 4 (Moving Charges and Magnetism), a straight conductor of length L carrying current I in a magnetic field B experiences a force F=BILsinθ, where θ is the angle between the current direction and the field. This macroscopic force is the collective effect of the Lorentz force on all the moving charges inside the wire. Since the wire is perpendicular to the field, θ=90∘ and sinθ=1. Substituting B=0.6 T, I=5 A, L=0.4 m: F=(0.6)(5)(0.4)=1.2 N. The value 0.6 N halves the answer, as if L=0.2 m. The value 12 N is ten times too large from a decimal-point error. The value 0.12 N is ten times too small for the same reason. Plausibility check: the units combine as T⋅A⋅m=N, and a force of about a newton on a short current-carrying wire in a strong field is entirely reasonable.
This easy difficulty physics question is from the chapter magnetic effects of current and magnetism, covering the topic of force on a current-carrying conductor. It appeared in the 2025 exam.
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