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CBSE Class 12 Physics 2025 All Sets Solved Paper

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Question : 3 of 16
Marks: +1, -0
A 1 cm segment of a wire lying along x-axis carries current of 0.5 A along +x direction. A magnetic field B=(0.4 mT)j+(0.6 mT)k is switched on, in the region. The force acting on the segment is
Solution:  
The forces on a current-carrying wire in a magnetic field is:
F=l(L×B)
Given:
I = 0.5A, L=1icmspacespaceB=(0.4mTj+0.6mTk)
Using cross product:
L×B=i×(0.4j+0.6k)
Using vector cross-product rules:
i×j=k,spacei×k=j
i(0.4j+0.6k)=0.4k0.6j
Multiply by I = 0.5:
F=(0.2k0.3j)
Length was in cm and magnetic field in mT.
So, in SI unit F=(0.2k0.3j)×105spaceN
F=(2k3j) µN
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