Q. No.The magnetic induction at point \(P\), which is \(4\) cm from a long current-carrying wire is \(10^{-8}\) Tesla. What would be the field of induction at a distance of \(12\) cm from the same current?
1.
\(3.33\times 10^{-9}\) Tesla
2.
\(1.11\times 10^{-4}\) Tesla
3.
\(3\times 10^{-3}\) Tesla
4.
\(9\times 10^{-2}\) Tesla
| 1. | At a distance \(\frac{d}{2}\) from any of the wires in any plane. |
| 2. | At a distance \(\frac{d}{3}\) from any of the wires in the horizontal plane. |
| 3. | Anywhere on the circumference of a vertical circle of radius \(d\) and centre halfway between the wires. |
| 4. | At points halfway between the wires in the horizontal plane. |
In the figure shown below there are two semicircles of radius \(r_1\) and \(r_2\) in which a current \(i\) is flowing. The magnetic induction at the centre of \(O\) will be:
1. \(\frac{\mu_{0} i}{r} \left(r_{1} + r_{2}\right)\)
2. \(\frac{\mu_{0} i}{4} \left[\frac{r_{1} + r_{2}}{r_{1} r_{2}}\right]\)
3. \(\frac{\mu_{0} i}{4} \left(r_{1} - r_{2}\right)\)
4. \(\frac{\mu_{0} i}{4} \left[\frac{r_{2} - r_{1}}{r_{1} r_{2}}\right]\)
In a current-carrying long solenoid, the field produced does not depend upon:
| 1. | Number of turns per unit length | 2. | Current flowing |
| 3. | Radius of the solenoid | 4. | All of the above |
Which one of the following gives the value of the magnetic field according to Biot-Savart’s law?
| 1. | \(\frac{{i} \Delta {l} \sin (\theta)}{{r}^2} \) | 2. | \(\frac{\mu_0}{4 \pi} \frac{i \Delta {l} \sin (\theta)}{r} \) |
| 3. | \(\frac{\mu_0}{4 \pi} \frac{{i} \Delta{l} \sin (\theta)}{{r}^2} \) | 4. | \(\frac{\mu_0}{4 \pi} {i} \Delta {l} \sin (\theta)\) |
What is the magnetic field at point \(O\) in the figure?
1. \(\frac{\mu_{0} I}{4 \pi r}\)
2. \(\frac{\mu_{0} I}{4 \pi r} + \frac{\mu_{0} I}{2 \pi r}\)
3. \(\frac{\mu_{0} I}{4 r} + \frac{\mu_{0} I}{4 \pi r}\)
4. \(\frac{\mu_{0} I}{4 r} - \frac{\mu_{0} I}{4 \pi r}\)
If the current is flowing in the south direction along a power line, then what will be the direction of the magnetic field above the power line (neglecting the earth's field)?
| 1. | South | 2. | East |
| 3. | North | 4. | West |
(Magnetic permeability of free space = \(\mu_0)\)
| 1. | \(\frac{\mu _{0}i}{2\pi a}\) | 2. | \(\frac{\mu _{0}i\sqrt2}{\pi a}\) |
| 3. | \(\frac{2\sqrt2\mu _{0}i}{\pi a}\) | 4. | \(\frac{\mu _{0}i}{\sqrt2\pi a}\) |
A proton and an \(\alpha\text-\)particle enter a uniform magnetic field perpendicularly at the same speed. If a proton takes \(25~\mu\text{s}\) to make \(5\) revolutions, then the periodic time for the \(\alpha\text-\)particle will be:
1. \(50~\mu\text{s}\)
2. \(25~\mu\text{s}\)
3. \(10~\mu\text{s}\)
4. \(5~\mu\text{s}\)
Which among the following options needs to be decreased to increase the sensitivity of a moving coil galvanometer?
| 1. | the number of turns in the coil. | 2. | the area of the coil. |
| 3. | the magnetic field. | 4. | the couple per unit twist of the suspension. |
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