Question

A straight wire of mass $200g$ and length $1.5m$ carries a current of $2A$. It is suspended in mid air by a uniform horizontal magnetic field $B$. The magnitude of $B$ (in tesla) is :

• A. $0.65$
• B. $0.55$
• C. $0.75$
• D. $0.45$

Answer 1

Answer: (A)

$0.65$

Given, mass of the wire $=200g=0.2kg$
Length of the wire $=15m$
Current $i=2A$
Magnetic field $B=$?
The force acting on the current carrying wire in uniform magnetic field
$F=Bil\sin \theta$
$F=Bil$ $(\because \theta ={90}^o)$
Weight of the wire $w=mg=0.2\times 9.8N$
In the position of suspension
$Bil=mg$
$B=\frac{mg}{il}=\frac{0.2\times 9.8}{2\times 15}=0.65T$