Magnetic Field Due to a Straight Long Wire

Q. Four infinite long wires carrying equal current are placed parallel and equidistant as shown in figure. Then magnitude of force per unit length.

1. on $2$ and $3$ are equal.
2. on $2$ is maximum.
3. on $1$ and $4$ are equal.
4. on $4$ is minimum

Q. Shown below is a semi-infinite wire carrying current I. What will be magnetic field at point P, which is d units away from one of its end?

1. $\frac{{\mu }_{0}I}{8\pi d}$
2. $\frac{{\mu }_{0}I}{d}$
3. $\frac{{\mu }_{0}I}{2\pi d}$
4. $\frac{{\mu }_{0}I}{4\pi d}$

Q.

The strength of the magnetic field at a point r near a long straight current carrying wire is B. The field at a distance $\frac{r}{2}$ will be

[MP PMT 1990]

1. 2B

2. 4B

3. 
   

4. 
   

Q. Two infinitely long insulated wires are kept perpendicular to each other. They carry currents $I_1=2A$ and $I_2=1.5A$.
i) Find the magnitude and direction of the magnetic field at P.
ii) If the direction of current is reversed in one of the wires. What would be the magnitude of the field B?

1. $2\times {10}^{-5}T$, normally into the plane of the paper, $2\sqrt{2}\times {10}^{-5}T$
2. $2\times {10}^{-5}T$, normally out of the plane of the paper, $2\sqrt{2}\times {10}^{-5}T$
3. $2\times {10}^{-5}T$, normally into the plane of the paper, Zero
4. $2\times {10}^{-5}T$, normally into the plane of the paper, Zero

Q.

Which of the following graphs shows the variation of magnetic induction B with distance r from a long wire carrying current

[NCERT 1984; MNR 1998; MP PMT]

1. 
   

2. 
   

3. 
   

4. 
   

Q. What will be the resultant magnetic field at origin due to four infinitely long wires. If each wire produces magnetic field 'B' at origin

1. $4B$
   
2. $Zero$
3. $\sqrt{2}B$
   
4. $2\sqrt{2}B$

Q. Two infinite length wires carries currents 8A and 6A respectively and placed along X and Y-axis. Magnetic field at a point P(0, 0, d)m will be

1. 
2. 
3. 
4. 

Q. An infinitely long conductor PQR is bent to form a right angle as shown. A current I flows through PQR The magnetic field due to this current at the point M is $H_1$. Now another infinitely long straight conductor QS is connected at Q so that the current is I/2 in QR as well as in QS, The current in PQ remaining unchanged. The magnetic field at M is now $H_2$ The ratio $\frac{H_1}{H_2}$ is given by

1. $\frac{1}{2}$
2. $1$
3. $\frac{2}{3}$
4. $2$

Q.

An electric current is flowing in a long straight wire. The magnetic field due to this current a distance of 5 cm from the wire is 10 T. The magnetic field at a distance of 10 cm from the wire is

1. 2.5 T

2. 5 T

3. 20 T

4. 40 T

Q.

Wires 1 and 2 carrying currents $i_1$ and $i_2$ respectively are inclined at an angle $\theta$ to each other. What is the force on a small element dl of wire 2 at a distance of r from wire 1 (as shown in figure) due to the magnetic field of wire1

1. 
2. 
3. 
4.