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Physics M.C.Q (1 Marks)

Magnetism And Matter · Rajasthan Board (RBSE) STD 12 Science (Rajasthan - English Medium). 234 questions.

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M.C.Q (1 Marks)

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Question 11 Mark
When the current through the electromagnet of a relay reaches a particular value:
Answer
  1. Both A or C.
Explanation:
They are ways of switching using a low current to use an electromagnet to close or open a spring steel contact.They are often used to isolate a user from a high voltage that needs to be switched, using low current, low voltage to operate the relay, rather than having a user come in direct proximity to the higher voltage that needs to be switched.When the current through the electromagnet of a relay reaches a particular value it either breaks the circuit by repllening or closes the circuit by pulling in an iron contact.
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Question 31 Mark
According to Lenz's law there is conversion of:
Answer
  1. Energy.
Explanation:
Lenz's law deals with conversion of mechanical energy into electromagnetic energy in case of electromagnetic induction. Hence Lenz's law is basically a conversion of energy from one form to another.
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Question 51 Mark
A toroid of n turns, mean radius R and cross-sectional radius a carries current I. It is placed on a horizontal table taken as x-y plane. It's magnetic moment m:
Answer
  1. Is zero, otherwise there would be a field falling as $\frac{1}{\text{r}^2}$ at large distances distances outside the toroid.
Solution:
Key concept: Toroid'. A toroid can be considered as a ring shaped closed solenoid. Hence it is like an endless cylindrical solenoid.

The magnetic field is only confined inside the body of a toroid in the form of concentric magnetic lines of force. For any point inside the empty space surrounded by toroid and outside the toroid, the magnetic field B is zero because the net current enclosed in these spaces is zero. Thus, the magnetic moment of toroid is zero.
In general, if we take r as a large distance outside the toroid, then $\text{m}\propto\frac{1}{\text{r}^3}$. But this case is not possible here.
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Question 61 Mark
Two short magnets of equal dipole moments $M$ are fastened perpendicularly at their centre $($figure$).$ The magnitude of the magnetic field at a distance $d$ from the centre on the bisector of the right angle is:
Answer

Magnetic field $(B_1)$ due to the short dipole $A$ of dipole moment $M$ at an axial point is given by,
$\vec{\text{B}_1}=\frac{\mu_0}{4\pi}\frac{2\text{M}}{\text{d}^3}\dots(1)$
Magnetic field $(B_2)$ due to the short dipole $B$ of dipole moment $M$ at an axial point is given by,
$\vec{\text{B}_2}=\frac{\mu_0}{4\pi}\frac{2\text{M}}{\text{d}_3}\dots(2)$
Resultant magnetic field $(B)$ will be,
$\text{B}=\sqrt{\text{B}_1^2+\text{B}_2^2}$
$\text{B}=\frac{\mu_0}{4\pi}\frac{\sqrt[2]{2}\text{M}}{\text{d}^3}$
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Question 71 Mark
Let the magnetic field on earth be modelled by that of a point magnetic dipole at the centre of earth. The angle of dip at a point on the geographical equator:
Answer
  1. Can be zero at specific points.
  2. Can be positive or negative.
  3. Is bounded.
Key concept: Angle of inclination or dip is the angle between the direction of intensity of total magnetic field of the earth and a horizontal line in the magnetic meridian.

If the total magnetic field of the earth is modelled by a point magnetic dipole at the centre, then it is in the same plane of geographical equator, thus the angle of dip at a point on the geographical equator is bounded in a range from positive to negative value.
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Question 81 Mark
The magnetic field of Earth can be modelled by that of a point dipole placed at the centre of the Earth. The dipole axis makes an angle of 11.3º with the axis of Earth. At Mumbai, declination is nearly zero. Then:
Answer
  1. The declination varies between 11.3ºW to 11.3ºE.
Solution:
The magnetic field lines of the earth resemble that of a hypothetical magnetic dipole located at the centre of the earth.
The axis of the dipole does not coincide with the axis of rotation of the earth and it is tilted at some angle (angle of declination). Here in this situation the angle of declination is approximately 11.3º with respect to the later. Here two possibilities arises as shown in the figure below.
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Question 91 Mark
Consider a magnetic dipole kept in the north to south direction. Let $P_1, P_2, Q_1, Q_2$ be four points at the same distance from the dipole towards north, south, east and west of the dipole respectively. The directions of the magnetic field due to the dipole are the same at:
Answer

We know that magnetic field lines are directed from the north pole to the south pole.
From the given figure,
we can say that the direction of magnetic field $\overrightarrow{\text{B}}$ is the same only at points $P_1$ and $P_2$ and at points $Q_1$ and $Q_{2.}$
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Question 101 Mark
The hysteresis cycle curve for the material of a permanent magnet is:
Answer
  1. Tall and wide.
Explanation:
Hysteresis cycle curve for the material of a permanent magnet is given in the image.
It is clear from the image that hysteresis cycle curve for the material of a permanent magnet is tall and wide.
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Question 111 Mark
Core of electromagnets are made of ferromagnetic material which has:
Answer
  1. High permeability and Low retentivity.
Explanation:
Electromagnetic cores should have:
  1. High permeability so that it supports the formation of a magnetic field within itself.
  2. Low retentivity so that the magetic field so that it gets demagnetized easily.
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Question 121 Mark
A thin diamagnetic rod is placed vertically between the poles of an electromagnet. When the current in the electromagnet is switched on, then the diamagnetic rod is pushed up, out of the horizontal magnetic field. Hence, the rod gains gravitational potential energy. The work required to do this comes from:
Answer
  1. The current source.
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Question 131 Mark
Curie temperature is the temperature above which:
Answer
  1. A ferromagnetic material becomes paramagenetic.
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Question 141 Mark
Two points A and B are situated at a distance x and 2x respectively from the nearer pole of a magnet 2cm long. The ratio of magnetic field at A and B is:
Answer
  1. 8 : 1 approximately.
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Question 151 Mark
Core of elctromagnets are made of ferromagnetic materials which have:
Answer
  1. High permeability and high retentivity.
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Question 171 Mark
The upper limit temperature of a super conductor is:
Answer
  1. 125K
Explanation:
Superconductors are materials that conduct electricity with no resistance. This means that, unlike the more familiar conductors such as copper or steel, a superconductor can carry a current indefinitely without losing any energy.
The upper limit temperature of a superconductor is 125K
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Question 181 Mark
The substances which are attracted towards a magnet are called _______.
Answer
  1. Ferro-magnetic materials
Explanation:
The substances which are attracted towards a magnet are called ferro-magnetic materials Materials that can be magnetized, which are also the ones that are strongly attracted to a magnet, are called ferromagnetic (or ferrimagnetic). These include iron, nickel, cobalt, some alloys of rare-earth metals, and some naturally occurring minerals such as lodestone.
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Question 201 Mark
Permanent magnets should have:
Answer
  1. High retentivity and high coercivity.
Explanation:
Permanent magnets should have high retentivity so that a strong magnetic field persists on removal of magnetic field.
Permanent magnets should have high coercivity so that external magnetic field in opposite direction cannot easily demagnetize the magnet.
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Question 211 Mark
When does a magnetic dipole possess maximum potential energy inside a magnetic field?
Answer
  1. Magnetic moment and magnetic field are antiparallel.
Explanation:
A magnetic dipole possess maximum potential energy when its magnetic moment and the magnetic field are antiparallel. When the magnetic dipole is aligned along the magnetic field, i.e. when $θ = 180^\circ,$ it is in unstable equilibrium having maximum potential energy.
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Question 221 Mark
The hysteresis cycle for the material of permanent magnet is:
Answer
  1. Tall and wide.
Explanation:
Permanent magnet should have large coercivity and large retentivity. Therefore, the hysteresis cycle of the material should be tall and wide.
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Question 231 Mark
The line of force in a magnetic field represents the direction at each point that a magnetic needle placed at the point takes up. Do they also represent the direction of the force on a moving charge at each point?
Answer
  1. Not possible.
Explanation:
No. The force on a charge is perpendicular to the direction of the magnetic field at each point.
F = q (v × B).
It is inappropriate to call magnetic field lines as lines of force.
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Question 241 Mark
The value of Curie temperature for Ni is nearly:
Answer
  1. 631K
Explanation:
Above 631K Ni behaves like paramagnetic material.
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Question 251 Mark
The inherent property of all materials is:
Answer
  1. Diamagnetism.
Explanation:
Diamagnetism (where orbital motion of electrons creates tiny atomic current loops, which produce magnetic fields) is a property of all materials and opposes applied magnetic fields, but is very weak.
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Question 261 Mark
The permanent magnetic moment of the atoms of a material is zero. The material:
Answer
  1. Must be diamagnetic.
Explanation:
The permanent magnetic moment of the atoms of a material is zero. The material must be diamagnetic.
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Question 271 Mark
Lenz's law is a consequence of the law of conservation of:
Answer
  1. Energy.
Explanation:
According to Lenz's law an induced electromotive force (emf) always gives rise to a current whose magnetic field opposes the original change in magnetic flux.
It is a common way of understanding how electromagnetic circuits obey newton's third law and the conservation of energy.
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Question 281 Mark
Magnetic field can be defined as the:
Answer
  1. Space surrounding the magnet in which magnetic force acts.
Explanation:
A magnetic field is generated when electric charge carriers such as electrons move through space or within an electrical conductor. It is the space surrounding the magnet in which magnetic force acts. Its intensity is represented by magnetic lines of force.
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Question 291 Mark
In the hysteresis cycle, the value of H needed to make the intensity of magnetism zero is called:
Answer
  1. Coercive force.
Explanation:
The value of H needed to remove the residual magnetism is coercive force or coercivity.
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Question 301 Mark
The permanent magnetic moment of the atoms of a material is not zero. The material:
Answer
  1. Must be ferromagnetic
Explanation:
Unlike paramagnetic materials, the atomic moments in ferromagnetic materials exhibit very strong interactions. These interactions are produced by electronic exchange forces and result in a parallel or antiparallel alignment of atomic moments.
This results in permanent non-zero magnetic moment of atoms in these materials.
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Question 311 Mark
Which of the following statements can help you to determine the direction of induced current in Electromagnetic Induction?
Answer
  1. Induced current flows such that direction of magnetic field produced from induced current opposes change in external magnetic field.
Explanation:
Lenz's Law states that the direction of an induced current is always such as to oppose the change in the circuit or the magnetic field that produces it. So according to this law, induced current flows to oppose the cause.
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Question 321 Mark
The magnetic force required to demagnetise the material is:
Answer
  1. Coercivity.
Explanation:
Coercivity is the magnetic force required to demagnetise the material.
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Question 341 Mark
Consider the two idealized systems: (i) a parallel plate capacitor with large plates and small separation and (ii) a long solenoid of length L > > R, radius of cross-section. In (i) E is ideally treated as a constant between plates and zero outside. In (ii) magnetic field is constant inside the solenoid and zero outside. These idealised assumptions, however, contradict fundamental laws as below:
Answer
  1. Case (ii) contradicts Gauss’s law for magnetic fields.
Solution:
Key concept: The electrostatic field lines, do not form a continuous closed path (this follows from the conservative nature of electric field) while the magnetic field lines form the closed paths.
According to the Gauss' law, $\oint\text{E.ds}=\frac{\text{q}}{\epsilon_0}$ for electronstatic field. It does not contradict foe eletrostatic fields as the elecric field lines do not form a continuous closed path.
According to Gauss' law in magnetism.
$\oint\text{B.ds}=0$
Which implies that number of magnetic field lines entering the Gaussian surface is equal to the number of magnetic field lines leaving it. Therefore case (ii) is not possible.
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Question 351 Mark
If $\mu_0$is absolute permeability of vacuum and $\mu\text{r}$ is relative magnetic permeability of another medium, then permeability $\mu$ of the medium is:
Answer
  1. $\mu\ \mu_\text{r}$
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Question 361 Mark
Which one of the following, when suspended freely, slowly sets itself parallel to the direction of the magnetic field?
Answer
  1. Paramagnetic materials.
Explanation:
Paramagnetic materials are those when suspended freely inside the magnetic field, it slowly sets itself parallel to the direction of the magnetic field. When placed in a non-uniform magnetic field, it tends to move from weaker to a stronger magnetic field.
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Question 371 Mark
A magnetic field can be produced by:
Answer
  1. Both of these.
Explanation:
A moving charge and changing electric field both produces magnetic field.
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Question 381 Mark
The narrowest hysterisis loop is for:
Answer
  1. Soft magnetic material
Explanation:
A narrow hysteresis loop implies a small amount of dissipated energy. This occurs as a result of its small area and therefore more frequently repeated reversals of applied magnetising force. Soft magnetic are materials used in devices that require alternating magnetic fields have these narrow hysteresis shapes.
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Question 391 Mark
Permanent magnets are made from:
Answer
  1. Ferromagnetic substances.
Explanation:
Ferromagnetic substance, Because they get magnetize in external magnetic field and don't lose their magnetic property.
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Question 401 Mark
Which of the following group is diamagnetic?
Answer
  1. Copper, hydrogen, silver.
Explanation:
Diamagnetic substances are those which are freebly repelled by the magnetic field.
$\therefore$ Copper, Hydrogen, Silver are diamagnetic as their atoms have net magnetic dipole moment zero.
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Question 411 Mark
When a straight wire is moved up and down rapidly between two poles of a horseshoe magnet then _______ is produced in the wire.
Answer
  1. Electric current
Explanation:
An electric current is produced in the wire. The production of electricity from magnetism is called electromagnetic induction.
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Question 421 Mark
A space or region around a magnet in which a force is experienced by magnetic pole is called.
Answer
  1. Magnetic field
Explanation:
A surrounding around a magnet in which source is felt is due to magnetic property of the magnet term as magnetic field.
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Question 441 Mark
The curie weiss law is obeyed by iron:
Answer
  1. Above the curie temperature.
Explanation:
Curie - Wiess Law states that all ferromagnetic substances become paramagnteic above the curie temperature.
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Question 451 Mark
Find the false statement.
Answer
  1. Magnetic intensity and intensity of magnetization are the same.
Explanation:
The statement magnetic intensity and intensity of magnetization are the same is the false one. They are not the same. When a magnet is entering a magnetic field, then the poles of the magnet experiences certain forces. Magnetic intensity refers to the measure of these forces. But, the intensity of magnetization explains the change in the magnetic moment of a magnet as a function of volume. All the other statements are valid.
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Question 461 Mark
A magnetic needle of magnetic moment $6.7 \times 10^{-2} Am^2$ and moment of inertia $7.5 \times 10^{-6}kg m^2$ is performing simple harmonic oscillations in a magnetic field of $0.01 T.$ Time taken for $10$ complete oscillations is:
Answer
SELF
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Question 471 Mark
A horse-shoe magnet is an example of ________.
Answer
  1. Artificial magnet.
Explanation:
Artificial magnets are man-made magnets. Magnets that are made from iron in different components shapes and sizes for different uses are called artificial magnets.
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Question 481 Mark
Which of the following is another term for magnetization?
Answer
  1. Magnetic polarization.
Explanation:
Magnetization is also termed as magnetic polarization. Magnetic polarization is basically a balance between the magnetic flux density in a space which is devoid of matter and the magnetic flux density in a space with matter, i.e. in a material.
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Question 491 Mark
A circular coil and a bar magnet moves with the same velocity. Then
Answer
  1. There will be no induced emf in the coil.
Explanation:
Since the coil and the magnet are moving with same velocity, so there will be no change in magnetic flux linked with the coil due to magnet. Hence no emf is induced in the coil.
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Question 501 Mark
Materials suitable for permanent magnet, must have which of the following properties?
Answer
  1. High retentivity, high coercivity and high permeability.
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M.C.Q (1 Marks) - Physics STD 12 Science Questions - Vidyadip