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Permanent Magnets · Rajasthan Board (RBSE) STD 12 Science (Rajasthan - English Medium). 6 questions.

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Question 11 Mark
Can the earth's magnetic field be vertical at a place? What will happen to a lreely suspended magnet at such a place? What is the value of dip here?
Answer
The magnetic lines of force at the poles of Earth are vertical due to which the magnetic needle becomes vertical. the needle dips vertically.
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Question 21 Mark
Can we have a single north pole? A single south pole?
Answer
No we cannot have single pole magnet.A magnet always has two poles.
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Question 31 Mark
Do two distinct poles actually exist at two nearby points in a magnetic dipole?
Answer
No, in a magnetic dipole there are only two distinct poles that are at the ends.
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Question 41 Mark
Magnetic scalar potential is defined as$\text{U}(\overrightarrow{\text{r}_2})-\text{U}(\overrightarrow{\text{r}_1})=-\int\limits^{\vec{\text{r}}_2}_{\vec{\text{r}_1}} \vec{\text{B}}.\text{d}\vec{\text{l}}.$
Apply this equation to a closed curve enclosing a long atraicht wire. The RHS of the above equation is then $-{\mu}_\text{o} \text{ i}$ by Ampere's law. We see that $\text{U}(\vec{\text{r}_2})\neq\text{U}(\vec{\text{r}_1})$ even when $\vec{\text{r}_2}=\vec{\text{r}_1}.$Can we have a magnetic acalar potential in this case?
Answer
Yes we can have magnetic potential scalar in this case.
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Question 51 Mark
To measure the magnetic moment of a bar magnet, one may use:
  1. A tangent galvanometer.
  2. A deflection galvanometer if the earth's horizontal field is known.
  3. An oscillation magnetometer if the earth's horizontal field is known.
  4. Both deflection and oscillation magnetometer if the earth's horizontal field is not nown.
Answer
  1. A deflection galvanometer if the earth's horizontal field is known.
  2. An oscillation magnetometer if the earth's horizontal field is known.
  3. Both deflection and oscillation magnetometers if the earth's horizontal field is not know.
Denial of $(a):$
Tangent galvanometer is an instrument used to measure electric current; it cannot be used to the measure magnetic moment of a bar magnet.
Justification of $(b)$ and $(c):$
Deflection magnetometer is used to measure $\frac{\text{M}}{\text{B}_\text{H}}$ of a permanent bar magnet.
Similarly, oscillation magnetometer is used to measure $M \ B_H$ of a bar magnet.
So, if earth's horizontal field $, B_H,$ is known, then the magnetic moment of a bar magnet $, M,$ can be measured.
Justification of $(d)$:
Using deflection and oscillation magnetometers, we can calculate $\text{MBHMBH}$ and $M \ B_H,$ respectively.
Therefore, if we multiply the result obtained from both the instruments, then $B_H$ cancels out as $\frac{\text{M}}{\text{B}_\text{H}}\times\text{MB}_\text{H}=\text{M}^2$.
Thus, the value of $B_H$ is not required.
Therefore, we can use both deflection and oscillation magnetometers if the earth's horizontal field is not known.
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