A moving coil galvanometer has N number of turns in a coil of effective area A, it carries a current I. The magnetic field B is radial. The torque acting on the coil is 

(1) $N{A}^2{B}^{2}I$                          

(2) $NAB{I}^2$

(3) $N^{2}ABI$                            

(4) $NABI$

Three long, straight, and parallel wires carrying currents of \(30\) A, \(10\) A, and \(20\) A in \(P\), \(Q\), and \(R\), respectively, are arranged as shown in the figure. What is the force experienced by a \(10\) cm length of wire \(Q\)?

A non-planar loop of conducting wire carrying a current I is placed as shown in the figure. Each of the straight sections of the loop is of length 2a. The magnetic field due to this loop at the point P (a,0,a) points in the direction

(a)  $\frac{1}{\sqrt{2}}\left(-\hat{\mathrm{j}}+\hat{\mathrm{k}}\right)$                                   (c) $\frac{1}{\sqrt{3}}(\hat{\mathrm{i}}+\hat{\mathrm{j}}+\hat{\mathrm{k}})$

(b)  $\frac{1}{\sqrt{3}}(-\hat{\mathrm{j}}+\hat{\mathrm{k}}+\hat{\mathrm{i}})$                               (d)  $\frac{1}{\sqrt{2}}(\hat{\mathrm{i}}+\hat{\mathrm{k}})$                        

 A long straight wire along the z-axis carries a current I in the negative z-direction. The magnetic field vector $\overrightarrow{\mathrm{B}}$ at a point having coordinates (x, y) in the z = 0 plane is :

1. $\frac{{\mathrm{\mu }}_0\mathrm{I}(\mathrm{y}\hat{\mathrm{i}}-\mathrm{x}\hat{\mathrm{j}})}{2\mathrm{\pi }({\mathrm{x}}^2+{\mathrm{y}}^2)}$                 

2. $\frac{{\mathrm{\mu }}_0\mathrm{I}(\mathrm{x}\hat{\mathrm{i}}+\mathrm{y}\hat{\mathrm{j}})}{2\mathrm{\pi }({\mathrm{x}}^2+{\mathrm{y}}^2)}$

3. $\frac{{\mathrm{\mu }}_0\mathrm{I}(\mathrm{x}\hat{\mathrm{j}}-\mathrm{y}\hat{\mathrm{i}})}{2\mathrm{\pi }({\mathrm{x}}^2+{\mathrm{y}}^2)}$                 

4. $\frac{{\mathrm{\mu }}_0\mathrm{I}(\mathrm{x}\hat{\mathrm{i}}-\mathrm{y}\hat{\mathrm{j}})}{2\mathrm{\pi }({\mathrm{x}}^2+{\mathrm{y}}^2)}$

A circular coil is in y-z plane with centre at origin. The coil is carrying a constant current. Assuming direction of magnetic field at x = – 25 cm to be positive direction of magnetic field, which of the following graphs shows variation of magnetic field along x-axis

The ratio of the magnetic field at the centre of a current carrying circular wire and the magnetic field at the centre of a square coil made from the same length of wire will be

(a) $\frac{{\mathrm{\pi }}^2}{4\sqrt{2}}$                             (b) $\frac{{\mathrm{\pi }}^2}{8\sqrt{2}}$

(c) $\frac{\mathrm{\pi }}{2\sqrt{2}}$                             (d) $\frac{\mathrm{\pi }}{4\sqrt{2}}$ 

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

(a) $\frac{\sqrt{2}{\mu }_{0}i}{3\mathrm{\pi a}}\odot$                                  (b) $\frac{\sqrt{2}{\mu }_{0}i}{3\mathrm{\pi a}}\otimes$

(c) $\frac{\sqrt{2}{\mu }_{0}i}{\mathrm{\pi a}}\odot$                                   (d) $\frac{\sqrt{2}{\mu }_{0}i}{\mathrm{\pi a}}\otimes$   

When a positively charged particle moves in an \(x\text-y\) plane, its path abruptly changes due to the presence of electric and/or magnetic fields beyond \(P\). The curved path is depicted in the \(x\text-y\) plane and is discovered to be noncircular. Which of the following combinations is true?
          
1. \(\vec{{E}}=0 ; \vec{{B}}={b} \hat{i}+{c} \hat{k}\) 
2. \(\vec{E}={a\hat{i}} ; \vec{B}={c} \hat{k}+a\hat{i}\)
3. \(\vec{E}=0 ; \vec{B}=c \hat{j}+b \hat{k}\)
4. \(\vec{E}=a\hat i ; \vec{B}=c\hat{k}+{b}\hat{j}\)

Figure shows the cross-sectional view of the partially hollow cylindrical conductor with inner radius 'R' and outer radius '2R' carrying uniformly distributed current along it's axis. The magnetic induction at point 'P' at a distance $\frac{3R}{2}$ from the axis of the cylinder will be:

1. Zero                               

2. $\frac{5{\mu }_{0}i}{72\mathrm{\pi R}}$

3. $\frac{7{\mu }_{0}i}{18\mathrm{\pi R}}$                             

4.  $\frac{5{\mu }_{o}i}{36\mathrm{\pi R}}$

A long wire AB is placed on a table. Another wire PQ of mass 1.0 g and length 50 cm is set to slide on two rails PS and QR. A current of 50A is passed through the wires. At what distance above AB, will the wire PQ be in equilibrium

(1) 25 mm                           

(2) 50 mm

(3) 70 mm                           

(4) 100 mm