Question
Figure shows a square loop ABCD with edge length a. The resistance of the wire ABC is r and that of ADC is 2r. The value of magnetic field at the centre of the loop assuming uniform wire is
Answer: Option B
:
B
According to question resistance of wire ADC is twice that of wire ABC. Hence current flows through ADC is half that of ABC i.e. i2i1=12. Also i1+i2=i⇒i1=2i3 and i2=i3
Magnetic field at centre O due to wire AB and BC (part 1 and 2) B1=B2=μ04π.2i1sin45∘a/2⊗=μ04π.2√2i1a⊗
and magnetic field at centre O due to wires AD and DC (i.e. part 3 and 4) B3=B4=μ04π2√2I2a⊙
Also i1=2i2. So (B1=B2)>(B3=B4)
Hence net magnetic field at centre O
Bnet=(B1+B2)−(B3+B4)
=2×μ04π.2√2×(23i)a−μ04π.2√2(i3)×2a
=μ04π.4√2i3a(2−1)⊗=√2μ0i3πa⊗
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B
According to question resistance of wire ADC is twice that of wire ABC. Hence current flows through ADC is half that of ABC i.e. i2i1=12. Also i1+i2=i⇒i1=2i3 and i2=i3
Magnetic field at centre O due to wire AB and BC (part 1 and 2) B1=B2=μ04π.2i1sin45∘a/2⊗=μ04π.2√2i1a⊗
and magnetic field at centre O due to wires AD and DC (i.e. part 3 and 4) B3=B4=μ04π2√2I2a⊙
Also i1=2i2. So (B1=B2)>(B3=B4)
Hence net magnetic field at centre O
Bnet=(B1+B2)−(B3+B4)
=2×μ04π.2√2×(23i)a−μ04π.2√2(i3)×2a
=μ04π.4√2i3a(2−1)⊗=√2μ0i3πa⊗
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