Magnetic Materials — NEET Physics PYQ MCQs with Solutions
Free NEET Physics PYQ Magnetic Materials MCQs with step-by-step solutions (13 questions). Part of Magnetism and Matter. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Magnetic Materials · easy · numerical
An iron rod of susceptibility 599 is subjected to a magnetising field of $1200\,\text{A m}^{-1}$. The permeability of the material of the rod is (Take, $\mu_0=4\pi\times10^{-7}\,\text{T m A}^{-1}$)
A. $8.0\pi\times10^{-5}\,\text{T m A}^{-1}$
B. $2.4\pi\times10^{-5}\,\text{T m A}^{-1}$
C. $2.4\pi\times10^{-7}\,\text{T m A}^{-1}$
D. $2.4\pi\times10^{-4}\,\text{T m A}^{-1}$ ✓ Correct
Solution: Permeability $\mu=\mu_0(1+\chi_m)=4\pi\times10^{-7}\times(1+599)=4\pi\times10^{-7}\times600=2.4\pi\times10^{-4}\,\text{T m A}^{-1}$.
Q2 — Magnetic Materials · medium · theory
A thin diamagnetic rod is placed vertically between the poles of an electromagnet. When the current in the electromagnet is switched on, 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
A. the lattice structure of the material of the rod
B. the magnetic field
C. the current source ✓ Correct
D. the induced electric field due to the changing magnetic field
Solution: A diamagnetic substance is repelled from the stronger field region and moves to the weaker field region, gaining gravitational potential energy. This energy is supplied by the current source that maintains the magnetic field against the back-reaction of the moving rod.
Q3 — Magnetic Materials · easy · theory
The magnetic susceptibility is negative for
A. paramagnetic material only
B. ferromagnetic material only
C. paramagnetic and ferromagnetic materials
D. diamagnetic material only ✓ Correct
Solution: Relative permeability $\mu_r=1+\chi_m$. For diamagnetic substances $\mu_r<1$, so $\chi_m$ is negative. For paramagnetic and ferromagnetic substances $\chi_m$ is positive.
Q4 — Magnetic Materials · easy · theory
There are four light weight rod samples $A$, $B$, $C$ and $D$ separately suspended by thread. A bar magnet is slowly brought near each sample and the following observations are noted: (i) $A$ is feebly repelled (ii) $B$ is feebly attracted (iii) $C$ is strongly attracted (iv) $D$ remains unaffected. Which one of the following is true?
A. $C$ is of a diamagnetic material
B. $D$ is of a ferromagnetic material
C. $A$ is of a non-magnetic material
D. $B$ is of a paramagnetic material ✓ Correct
Solution: Diamagnetic materials are feebly repelled ($A$), paramagnetic materials are feebly attracted ($B$), ferromagnetic materials are strongly attracted ($C$), and materials with negligible susceptibility remain unaffected ($D$). So $B$ is paramagnetic.
Q5 — Magnetic Materials · easy · theory
If a diamagnetic substance is brought near the North or the South pole of a bar magnet, it is
A. repelled by both the poles ✓ Correct
B. repelled by the North pole and attracted by the South pole
C. attracted by the North pole and repelled by the South pole
D. attracted by both the poles
Solution: A diamagnetic substance gets weakly magnetised opposite to the applied field, so it tends to move from a region of stronger field to weaker field, i.e. it is repelled by both the North and South poles of a bar magnet.
Q6 — Magnetic Materials · easy · theory
Nickel shows ferromagnetic property at room temperature. If the temperature is increased beyond the Curie temperature, then it will show
A. paramagnetism ✓ Correct
B. anti-ferromagnetism
C. no magnetic property
D. diamagnetism
Solution: Above the Curie temperature, thermal agitation destroys the exchange coupling responsible for ferromagnetism, and the material becomes simply paramagnetic.
Q7 — Magnetic Materials · easy · theory
Above the Curie temperature,
A. a ferromagnetic substance becomes paramagnetic ✓ Correct
B. a paramagnetic substance becomes diamagnetic
C. a diamagnetic substance becomes paramagnetic
D. a paramagnetic substance becomes ferromagnetic
Solution: Ferromagnetism decreases with rising temperature. Above a definite (Curie) temperature, the persistent alignment of atomic dipoles breaks down and the ferromagnetic substance becomes simply paramagnetic.
Q8 — Magnetic Materials · medium · theory
If the magnetic dipole moment of an atom of diamagnetic material, paramagnetic material and ferromagnetic material are denoted by $\mu_d$, $\mu_p$ and $\mu_f$ respectively, then
A. $\mu_d=0$ and $\mu_f\ne 0$
B. $\mu_d\ne 0$ and $\mu_f=0$
C. $\mu_d=0$ and $\mu_p\ne 0$ ✓ Correct
D. $\mu_p\ne 0$ and $\mu_f=0$
Solution: In diamagnetic substances, electron spins in each pair are opposite and cancel, so the atomic magnetic moment $\mu_d=0$. Paramagnetic and ferromagnetic substances have atoms with a net excess of unpaired spins, so $\mu_p\ne 0$ (and $\mu_f\ne 0$).
Q9 — Magnetic Materials · easy · theory
According to Curie's law, the magnetic susceptibility of a paramagnetic substance at an absolute temperature $T$ is proportional to
A. $\dfrac{1}{T^2}$
B. $T^2$
C. $\dfrac{1}{T}$ ✓ Correct
D. $T$
Solution: Curie's law states that the magnetic susceptibility of a paramagnetic substance is inversely proportional to its absolute temperature, i.e. $\chi_m\propto \dfrac{1}{T}$.
Q10 — Magnetic Materials · easy · theory
A diamagnetic material in a magnetic field moves
A. perpendicular to the field
B. from weaker to the stronger parts of the field
C. from stronger to the weaker parts of the field ✓ Correct
D. None of the above
Solution: A diamagnetic material is magnetised opposite to the external field, so it experiences a net force pushing it from stronger to weaker parts of a non-uniform magnetic field.
Q11 — Magnetic Materials · easy · theory
In which type of material does the magnetic susceptibility not depend on temperature?
A. Diamagnetic ✓ Correct
B. Paramagnetic
C. Ferromagnetic
D. Ferrite
Solution: Diamagnetism arises from induced currents in electron orbits and does not depend on thermal agitation, so the magnetic susceptibility of a diamagnetic substance is independent of temperature.
Q12 — Magnetic Materials · easy · theory
A diamagnetic substance is brought near a strong magnet, then it is
A. attracted by the magnet
B. repelled by the magnet ✓ Correct
C. repelled by the North pole and attracted by the South pole
D. attracted by the North pole and repelled by the South pole
Solution: A diamagnetic substance is feebly magnetised opposite to the applied field, so near a strong magnet it is repelled by the magnet (by both its poles).
Q13 — Magnetic Materials · easy · theory
For protecting a sensitive equipment from the external magnetic field, it should be
A. placed inside an aluminium can
B. placed inside an iron can ✓ Correct
C. wrapped with insulation around it when passing current through it
D. surrounded with fine copper sheet
Solution: Iron is a ferromagnetic (high permeability) material, so magnetic field lines get concentrated within it and effectively excluded from the enclosed region. Placing the equipment inside an iron can shields it from the external magnetic field.