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Physics 1 Marks Question

Magnetism and Matter · Gujarat Board (GSEB) STD 12 Science (GSEB - English Medium). 20 questions.

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Question 11 Mark
Find two paramagnetic substances from the list below: Sodium (Na), Bismuth (Bi), Copper (Cu), Aluminium (Al), Lead (Pb).
Answer
Sodium and Aluminium
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Question 21 Mark
How should a magnetic dipole be placed in a uniform magnetic field so that its potential energy is maximum?
Answer
Its magnetic moment should be in opposite direction of $\overrightarrow{ m } \cdot \overrightarrow{ B }$
$\because$ In this condition, $\theta=180^{\circ}$ and $U =-m B \cos \theta$
$U =-m B \cos 180^{\circ}=-m B \times(-1)$
$U =m B$
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Question 31 Mark
A magnet of magnetic moment m is first cut perpendicular to its length and then perpendicular to its breadth into n equal parts, then calculate magnetic moment of each part.
Answer
Magnetic moment of each part $=\frac{m}{n} \times \frac{ L }{n}=\frac{m L}{n^2}$
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Question 51 Mark
Write relation between relative permeability $\mu_r$ magnetic permeability $\mu$ and magnetic permeability in vacuum $\mu_0$
Answer
$\mu_r=\frac{\mu}{\mu_0}$ or $\mu=\mu_r \mu_0$
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Question 61 Mark
Write relation between magnetic induction B, magnetic field H and intensity of magnetisation I.
Answer
$B =\mu_0( H +1)$ where $\mu_0$ is permeability of vacuum
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Question 71 Mark
Define magnetic permeability.
Answer
Ratio of magnetic induction B induced inside a substance to magnetic field H is known as magnetic permeability of the substance.
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Question 81 Mark
Define intensity of magnetisation.
Answer
Magnetic moment ( m ) generated in unit volume of a substance is called intensity of magnetisation.
$\overrightarrow{I}=\frac{\overrightarrow{m}}{V}$
It is a vector quantity and its unit is $A / m$.
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Question 111 Mark
Magnetic substances which experience force of repulsion in any non-uniform magnetic field are known by what name?
Answer
Diamagnetic substances
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Question 121 Mark
Write a relation between magnetising field $B$, magnetic field H and permeability $\mu$ of the medium.
Answer
$\mu=\frac{B}{H}$
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Question 131 Mark
Write a relation between permeability of the medium and magnetic susceptibility.
Answer
$\mu=\mu_0(1+\chi)$.
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Question 141 Mark
Define neutral point.
Answer
Such points where the resultant magnetic field due to the magnetic field of the magnet and the horizontal component of the earth's magnetic field is zero are known as neutral points.
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Question 151 Mark
"Magnetic field lines form closed curves." Why?
Answer
Since there is no existence of isolated pole, that is, poles always exist in pairs. Magnetic lines of force emerge from the north pole and move inside the south pole, hence they make closed curves.
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Question 161 Mark
What is the ratio of the intensities of the points situtated at equal distances from the midpoint of a short bar magnet on its axial and non-axial points?
Answer
$2: 1$
$\because \quad \overrightarrow{ B }_{\text {avial }}=\frac{\mu_0}{4 \pi}\left(\frac{2 \overrightarrow{m}}{ r ^3}\right)$ (For axial point)
and$\overrightarrow{B}_{\text {non-axial }}=\frac{\mu_0}{4\pi}\left(\frac{\overrightarrow{m}}{r^3}\right)$
(For non-axial points)
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Question 171 Mark
Write an expression for intensity of magnetisation field due to a small bar magnet of magnetic moment $\overrightarrow{ M }$ at a distance $r$ on its non-axial side.
Answer
$\overrightarrow{ B }=\frac{\mu_0}{4 \pi} \times\left(\frac{-\overrightarrow{ m }}{ r ^3}\right)$
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Question 181 Mark
Write an expression for intensity of magnetisation field at a point located at a distance $r$ on its axis due to a small bar magnet having magnetic moment $\overrightarrow{ m }$.
Answer
$\vec{B}=\frac{\mu_0}{4 \pi} \times \frac{2 \vec{m}}{r^3}$
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Question 191 Mark
Name the physical quantity whose unit is newton metre tesla ${ }^{-1}$ and whether is it scalar or vector?
Answer
$\tau_{\max }=m B \Rightarrow m=\frac{\tau_{\max }}{ B }$
On the basis of this formula, S.I. unit of M is newton metre tesla ${ }^{-1}$.
Hence, newton metre tesla ${ }^{-1}$ is S.I. unit of magnetic moment. It is a vector quantity.
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Question 201 Mark
Define magnetic moment.
Answer
Product of effective length and pole strength of a magnet is known as magnetic moment. It is a vector quantity whose direction is from south pole to the north pole. Its unit is ampere-metre ${ }^2$.
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