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Magnetism And Matter — Physics STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 SciencePhysicsMagnetism And Matter4 Marks
Question
When a ferromagnetic material goes through a hysteresis loop, its thermal energy is increased. Where does this energy come from?
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Answer

When a ferromagnetic material is taken through the cycle of magnetisation, magnet dipoles of the material orient and reorient with time. This molecular motion within the material results in the production of heat, which increses thermal energy of material.

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Net electric flux through a cube is the sum of fluxes through its six faces. Consider a cube as shown in figure, having sides of length L = 10.0cm. The electric field is uniform, has a magnitude E = 4.00 × 103N C-1 and is parallel to the xy plane at an angle of 37º measured from the + x - axis towards the + y - axis.

  1. Electric flux passing through surface S6 is:
  1. -24N m2 C-1
  2. 24N m2 C-1
  3. 32N m2 C-1
  4. -32N m2 C-1
  1. Electric flux passing through surface S1 is:
  1. -24N m2 C-1
  2. 24N m2 C-1
  3. 32N m2 C-1
  4. -32N m2 C-1
  1. The surfaces that have zero flux are:
  1. S1 and S3
  2. S5 and S6
  3. S2 and S4
  4. S1 and S2
  1. The total net electric flux through all faces of the cube is:
  1. 8N m2 C-1
  2. -8N m2 C-1
  3. 24N m2 C-1
  4. Zero.
  1. The dimensional formula of surface integral $\oint\vec{\text{E}}\cdot\text{d}\vec{\text{S}}$ of an electric field is:
  1. [M L2 T-2 A-1]
  2. [M L3 T-3 A-1]
  3. [M L-1 T3 A-3]
  4. [M L-3 T-3 A-1]
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Lenz's law states that the direction of induced current in a circuit is such that it opposes the change which produces it. Tims, if the magnetic flux linked with a closed circuit increases, the induced current flows in such a direction that a magnetic flux is created in the opposite direction of the original magnetic flux. If the magnetic flux linked with the closed circuit decreases, the induced current flows in such a direction so as to create a magnetic flux in the direction of the original flux.

  1. Which of the following statements is correct?
  1. The induced e.m.f is not in the direction opposing the change in magnetic flux so as to oppose the cause which produces it.
  2. The relative motion between the coil and magnet produces change in magnetic flux.
  3. Emf is induced only if the magnet is moved towards coil.
  4. Emf is induced only if the coil is moved towards magnet.
  1. The polarity of induced emf is given by:
  1. Ampere's circuital law.
  2. Biot-Savart law.
  3. Lenz's law.
  4. Fleming's right hand rule.
  1. Lenz's law is a consequence of the law of conservation of:
  1. Charge.
  2. Mass.
  3. Momentum.
  4. Energy.
  1. Near a circular loop of conducting wire as shown in the figure, an electron moves along a straight line. The direction of the induced current if any in the loop is:

  1. Variable.
  2. Clockwise.
  3. Anticlockwise.
  4. Zero.
  1. Two identical circular coils A and Bare kept in a horizontal tube side by side without touching each other. If the current in the coil A increases with time, in response, the coil B:
  1. Is attracted by A.
  2. Remains stationary.
  3. Is repelled.
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An amount n (in moles) of a monatomic gas at an initial temperature T0 is enclosed in a cylindrical vessel fitted with a light piston. The surrounding air has a temperature Ts(> T0) and the atmospheric pressure is Pa· Heat may be conducted between the surrounding and the gas through the bottom of the cylinder. The bottom has a surface area A, thickness x and thermal conductivity K. Assuming all changes to be slow, find the distance moved by the piston in time t.
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  2. $\frac{\pi\text{R}}{2}$
  3. $\frac{\pi\text{R}}{4}$
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  1. If the in tensity ratio of two coherent sources used in Young's double slit experiment is 49 : 1, then the ratio between the maximum and minimum intensities in the interference pattern is:
  1. 1 : 9
  2. 9 : 16
  3. 25 : 16
  4. 16 : 9
  1. The maximum intensity produced at D is given by:
  1. 4I0
  2. 2I0
  3. I0
  4. 3I0
  1. ln a Young's double slit experiment, the intensity at a point where the path difference is $\frac{\lambda}{6}$ ($\lambda$ - wavelength of the light) is I. If I0 denotes the maximum intensity, then I/I0 is equal to:
  1. $\frac{1}{2}$
  2. $\frac{\sqrt3}{2}$
  3. $\frac{1}{\sqrt2}$
  4. $\frac{3}{4}$
  1. Two identical light waves, propagating in the same direction, have a phase differenced. After they superpose the intensity of the resulting wave will be proportional to:
  1. $\cos\delta$
  2. $\cos\Big(\frac{\delta}{2}\Big)$
  3. $\cos^2\Big(\frac{\delta}{2}\Big)$
  4. $\cos^2\delta$
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Two q charges of the same nature are located at a distance d from each other, the third charge of value Q Coulomb is at the mid-point of the line joining them. For what value of Q will the system be in equilibrium?
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Draw a neat labelled diagram of human eye. Explain shortsightedness and longsightedness eye defects giving their cause and method of removal showing ray diagram.
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Radio waves are produced by the accelerated motion of charges in conducting wires. Microwaves are produced by special vacuum tubes. Infrared waves are produced by hot bodies and molecules also known as heat waves. UV rays are produced by special lamps and very hot bodies like Sun.

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  2. Longitudinal electromagnetic waves.
  3. Both longitudinal and transverse electromagnetic waves.
  4. None of these.
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  1. Infrared rays.
  2. Ultraviolet rays
  3. X-rays.
  4. Radiowaves.
  1. Biological importance of ozone layer is:
  1. It stops ultraviolet rays.
  2. It layer reduces greenhouse effect.
  3. It reflects radiowaves.
  4. None of these.
  1. Ozone is found in.
  1. Stratosphere.
  2. Ionosphere.
  3. Mesosphere.
  4. Troposphere.
  1. Earth's atmosphere is richest in.
  1. Ultraviolet.
  2. Infrared.
  3. X-rays.
  4. Microwave.
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Hydrogen spectrum consists of discrete bright lines in a dark background, and it is specifically known as hydrogen emission spectrum. There is one more type of hydrogen spectrum that exists where we get dark lines on the bright background, it is known as absorption spectrum. Balmer found an empirical formula by the observation of a small part of this spectrum, and it is represented by $\frac{1}{\lambda}=\text{R}\bigg(\frac{1}{2^2}-\frac{1}{\text{n}^2}\bigg)$ where n = 3, 4, 5 For Lyman series, the emission is from first state to nth state, for Paschen series, it is from third state to nth state, for Brackett series, it is from fourth state to nth state and for Pfund series, it is from fifth state to nth state.
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  1. 8
  2. 6
  3. 15
  4. $\infty$
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  1. Balmer series.
  2. Brackett series.
  3. Paschen series.
  4. Lyman series.
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  1. 1025A
  2. 1218A
  3. 4861A
  4. 18751A
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  1. A universal constant.
  2. A universal constants.
  3. Different for different elements.
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  1. Hydrogen atom is excited from ground state to another state with principal quantum number equal to 4. Then the number of spectral lines in the emission spectra will be.
  1. 3
  2. 5
  3. 6
  4. 2
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When an insulator is placed in an external field, the dipoles become aligned. Induced surface charges on the insulator establish a polarization field $\vec{\text{E}}_\text{i}$ in its interior. The net field $\vec{\text{E}}$ in the insulator is the vector sum of $\vec{\text{E}}_0$ and $\vec{\text{E}}_\text{i}$ as shown in the figure.

On the application of external electric field, the effect of aligning the electric dipoles in the insulator is called polarisation, and the field $\vec{\text{E}}_\text{i}$ is known as the polarisation field.

The dipole moment per unit volume of the dielectric is known as polarisation $(\vec{\text{P}}).$ For linear isotropic dielectrics, $\vec{\text{P}}=\chi\vec{\text{E}},$ where $\chi=$ electrical susceptibility of the dielectric medium.

  1. Which among the following is an example of polar molecule?
  1. O2
  2. H2
  3. N2
  4. HCI
  1. When air is replaced by a dielectric medium of constant K, the maximum force of attraction between two charges separated by a distance:
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  2. Remains unchanged.
  3. Decreases K times.
  4. Increases 2K times.
  1. Which of the following is a dielectric?
  1. Copper.
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  3. Antimony (Sb).
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  1. The centre of gravity of electrons and protons coincide.
  2. The centre of gravity of electrons and protons do not coincide.
  3. The charge distribution is always symmetrical.
  4. The dipole moment is always zero.
  1. When a comb rubbed with dry hair attracts pieces of paper. This is because the?
  1. Comb polarizes the piece of paper.
  2. Comb induces a net dipole moment opposite to the direction of field.
  3. Electric field due to the comb is uniform.
  4. Comb induces a net dipole moment perpendicular to the direction of field.
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