Questions
A copper wire of length 1 m and radius 1 mm is joined in series with an iron wire of length Z m and radius 3 mm and a current is passed through the wires. The ratio of the current density in the copper and iron wires is
detailed solution
Correct option is B
Current density J=iA = iπr2 ⇒ J1J2 = i1i2 × r22r12But the wires are in series, so they have the samecurrent, hence i1=i2. So J1J2 = r22r12=9:1Talk to our academic expert!
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Electrons emerge from an electron accelerator as a beam having a circular cross-section of diameter 3 mm. The beam current is 6 μA and electrons are travelling so fast that their speed can be taken as m/sec with an insignificant error. Electron density in the beam is :
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