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MODEL PAPER 4 Physics - MODEL PAPER 4

Bihar Board (BSEB) - STD 12 Science - Physics (BSEB - English Medium). 38 questions in this chapter.

Question types

MODEL PAPER 4 question types

38 questions across 6 question groups — pick any mix to generate a Physics paper with step-by-step answer keys.

38
Questions
6
Question groups
5
Question types
Sample Questions

MODEL PAPER 4 questions

One sample from each question group in this chapter. Select any group above to see the full set with answer keys.

Q 1M.C.Q [1M]1 Mark
An electron is revolving around a proton in a circular orbit of diameter 0.1 nm . It produces a magnetic field of $14 Wb / m ^2$ at the proton. What is angular speed of the electron?
  • A
    $4.4 \times 10^{16} rads ^{-1}$
  • B
    $8.8 \times 10^{16} rads ^{-1}$
  • C
    $6.4 \times 10^{16} rads ^{-1}$
  • D
    $1.4 \times 10^{16} rads ^{-1}$
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Q 2M.C.Q [1M]1 Mark
In the diagram, a prism of angle $30^{\circ}$ is used. A ray PQ is incident as shown. An emergent ray RS emerges perpendicular to the second face. The angle of deviation is:
Image
  • A
    $60^{\circ}$
  • B
    $0^{\circ}$
  • C
    $30^{\circ}$
  • D
    $45^{\circ}$
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Q 3M.C.Q [1M]1 Mark
An electron is moving round the nucleus of a hydrogen atom in a circular orbit of radius r . The Coulomb force $\vec{F}$ between the two is:
  • A
    $\kappa \frac{e^2}{r^3} \vec{r}$
  • B
    $-\kappa \frac{e^2}{r^3} \vec{r}$
  • C
    $-\kappa \frac{e^3}{s^3} \hat{r}$
  • D
    $\kappa \frac{e^2}{n^3} \hat{r}$
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Q 4M.C.Q [1M]1 Mark
How does the magnetic susceptibility $\chi$ of a paramagnetic material change with absolute temperature T?
  • A
    $\chi \propto e^T$
  • B
    $\chi \propto e^T$
  • C
    $\chi=$ constant
  • D
    $\chi \propto T^{-1}$
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Q 5M.C.Q [1M]1 Mark
A biconvex lens of focal length f is cut into two identical plano convex lenses. The focal length of each part will be
  • A
    2f
  • B
    $\frac{f}{2}$
  • C
    4f
  • D
    f
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Q 6Assertion (A) & Reason (B) MCQ1 Mark
Assertion  (A): If the distance between parallel plates a capacitor is halved and dielectric constant is made three times then the capacitance becomes six times.
Reason (R) : Capacitance of the capacitor does not depend upon the nature of the material of the plates of the capacitor.
  • A
    Assertion and reason both are correct statements and reason is correct explanation for assertion.
  • B
    Assertion and reason both are correct statements and reason is correct explanation for assertion.
  • C
    Assertion is correct statement but reason is wrong statement.
  • D
    Assertion is wrong statement but reason is correct statement.
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Q 7Assertion (A) & Reason (B) MCQ1 Mark
Assertion (A) : The quantity L/R possesses the dimension of time.
Reason (R): In order to reduce the rate of increase of current through a solenoid, we should increase the time constant.
  • A
    Both A and R are true and R is the correct explanation of A.
  • B
    Both A and R are true but R is not the correct explanation of A.
  • C
    A is true but R is false.
  • D
    A is false but R is true.
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Q 8Assertion (A) & Reason (B) MCQ1 Mark
Assertion (A) : Wavefront emitted by a point source of light in an isotropic medium is spherical.
Reason (R): Isotropic medium has same refractive index in all directions.
  • A
    Both A and R are true and R is the correct explanation of A.
  • B
    Both A and R are true but R is not the correct explanation of A.
  • C
    A is true but R is false.
  • D
    A is false but R is true.
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Q 9Assertion (A) & Reason (B) MCQ1 Mark
Assertion (A): In process of photoelectric emission, all emitted electrons do not have same kinetic energy.
Reason (R): If radiation falling on the photosensitive surface of metal consists of different wavelengths then energy acquired by electrons absorbing photons of different wavelengths shall be different.
  • A
    Both A and R are true and R is the correct explanation of A.
  • B
    Both A and R are true but R is not the correct explanation of A.
  • C
    A is true but R is false.
  • D
    A is false but R is true.
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Q 11Short Answer Type Questions [2M]2 Marks
Suppose you are given a chance to repeat the alpha-particle scattering experiment using a thin sheet of solid hydrogen in place of the gold foil. (Hydrogen is a solid at temperatures below 14 K). What results do you expect?
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Q 12Short Answer Type Questions [2M]2 Marks
Two identical circular loops, P and Q. each of radius r and carrying currents are kept in the parallel planes having a common axis passing through O. The direction of current in P is clockwise and in Q is anti-clockwise as seen from O which is equidistant from the loops P and Q. Find the magnitude of the net magnetic field at O.

Image
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Q 13Short Answer Type Questions [2M]2 Marks
A circular coil of 25 turns and radius 6.0 cm, carrying a current of 10 A, is suspended vertically in a uniform magnetic field of magnitude 1.2 T. The field lines run horizontally in the plane of the coil. Calculate the force and the torque on the coil due to the magnetic field. In which direction should a balancing torque be applied to prevent the coil from turning?
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Q 14Short Answer Type Questions [2M]2 Marks
Magnetic force is always normal to the velocity of a charge and therefore does no work. An iron nail held near a magnet, when released, increases its kinetic energy as it moves to cling to the magnet. What agency is responsible for this increase in kinetic energy if not the magnetic field?
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Q 153 Marks Question3 Marks
The absolute refractive index of air is 1.0003 and the wavelength of yellow light in a vacuum is $6000 \stackrel{\circ}{A}$ . Find the thickness of air column which will contain one more wavelength of yellow light than in the same thickness of vacuum.
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Q 163 Marks Question3 Marks
Write Einstein's photoelectric equation in terms of the stopping potential and the threshold frequency for a given photosensitive material. Draw a plot showing the variation of stopping potential vs. the frequency of incident radiation.
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Q 173 Marks Question3 Marks
A cell of emf E and internal resistance r is connected across a variable load resistor R. Draw the plots of the terminal voltage V versus (i) resistance R and (ii) current I.
It is found that when $R=4 \Omega$, the current is 1 A and when R is increased to $9 \Omega$, the current reduces to 0.5 A .Find the values of the emf E and internal resistance r.
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Q 193 Marks Question3 Marks
A horizontal straight wire 10 m long extending from east to west is falling with a speed of $5.0 ms^{-1}$, at right angles to the horizontal component of the earth's magnetic field, $0.30 \times 10^{-4} Wb m ^{-2}$.
a. What is the instantaneous value of the emf induced in the wire?
b. What is the direction of the emf?
c. Which end of the wire is at the higher electrical potential?
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Q 204 Marks Questions4 Marks
Coulomb's law states that the electrostatic force of attraction or repulsion acting between two stationary point charges is given by
Image

where F denotes the force between two charges $q _1$ and $q _2$ separated by a distance r in free space, $\varepsilon_0$ is a constant known as the permittivity of free space. Free space is a vacuum and may be taken to be air practically. If free space is replaced by a medium, then $\varepsilon_0$ is replaced by $\left(\varepsilon_0 k\right)$ or $\left(\varepsilon_0 \varepsilon_r\right)$ where k is known as dielectric constant or relative permittivity.

(i) In coulomb's law, $F =k \frac{q_1 q_2}{r^2}$, then on which of the following factors does the proportionality constant k depends?
(a) Nature of the medium between the two charges
(b) Distance between the two charges
(c) Electrostatic force acting between the two charges
(d) Magnitude of the two charges

(ii) Dimensional formula for the permittivity constant $\varepsilon_0$ of free space is
(a) $\left[ M ^{-1} L^3 T^2 A^2\right]$
(b) $\left[ ML ^{-3} T^4 A^2\right]$
(c) $\left[ M ^{-1} L^{-3} T^4 A^2\right]$
(d) $\left[ ML ^{-3} T^4 A^{-2}\right]$

(iii) The force of repulsion between two charges of 1 C each, kept 1m apart in vaccum is
(a) $\frac{1}{9 \times 10^9} N$
(b) $\frac{1}{9 \times 10^{12}} N$
(c) $9 \times 10^7 N$
(d) $9 \times 10^9 N$

(iv) Two identical charges repel each other with a force equal to 10 mgwt when they are 0.6 m apart in air. ( $g =$ $10 m s ^{-2}$ ). The value of each charge is
(a) 2 mC
(b) $2 \times 10^{-7} mC$
(c) $2 \mu C$
(d) 2 nC

OR

Coulomb's law for the force between electric charges most closely resembles with
(a) law of conservation of energy
(b) Newton's 2nd law of motion
(c) law of conservation of charge .
(d) Newton's law of gravitation
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Q 214 Marks Questions4 Marks
Electrons oscillating in a circuit give rise to radiowaves. A transmitting antenna radiates most effectively the radiowaves of wavelength equal to the size of the antenna. The infrared waves incident on a substance set into oscillation all its electrons, atoms and molecules. This increases the internal energy and hence the temperature of the substance.

(i) If $v_g, v_X$ and $v_m$ are the speeds of gamma rays, $X$-rays and microwaves respectively in vacuum, then
(a) $v_g>v_X>v_m$
(b) $v_g<v_X<v_m$
(c) $v_g>v_X>v_m$
(d) $v_g=v_X=v_m$

(ii) Which of the following will deflect in electric field?
(a) ultraviolet rays
(b) $\gamma$-rays
(c) X-rays
(d) cathode rays

(iii) $\gamma$-rays are detected by
(a) point contact diodes
(c) thermopiles
(b) ionization chamber
(d) photocells

OR

We consider the radiation emitted by the human body. Which one of the following statements is true?
i. The radiation emitted is in the infrared region
ii. The radiation is emitted only during the day.
iii. The radiation is emitted during the summers and absorbed during the winters.
iv. The radiation emitted lies in the ultraviolet region and hence it is not visible
(a) Option(iv) (iii) (b) Option (ii) (c) Option (d) Option (i)

(iv) The frequency of electromagnetic wave, which best suited to observe a particle of radius $3 \times 10^{-4} cm$ is the order of
(a) $10^{14} Hz$
(b) $10^{12} Hz$
(c) $10^{13} Hz$
(d) $10^{15} Hz$
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Q 22Long Answer Type Questions [5M]5 Marks
i. Draw a ray diagram showing the image formation by a compound microscope. Hence obtain the expression for total magnification when the image is formed at least distance of distinct vision.
iii. A compound microscope consists of an objective lens of focal length 2.0 cm and an eyepiece of focal length 6.0 cm. If they are separated by a distance of 24 cm, find the total magnification when the image is formed at infinity.
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Q 23Long Answer Type Questions [5M]5 Marks
Two point charges -q and q are located at points (0, 0, - a) and (0, 0, a) respectively.
i. Find the electrostatic potential at (0, 0, z) and (x, y, 0).
ii. How much work is done in moving a small test charge from the point (5, 0, 0) to (- 7, 0, 0) along the x-axis?
iii. How would your answer change if the path of the test charge between the same points is not along the x-axis but along any other random path?
iv. If the above point charges are now placed in the same positions in the uniform external electric field $\vec{E}$, what would be the potential energy of the charging system in its orientation of unstable equilibrium?
Justify your answer in each case
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Q 24Long Answer Type Questions [5M]5 Marks
A series LCR circuit is connected to an a.c. source having voltage $V=V_m \sin \omega t$. Derive the expression for the instantaneous current I and its phase relationship to the applied voltage. Obtain the condition for resonance to occur. Define power factor. State the conditions under which it is
i. maximum and
ii. minimum.
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Q 25Long Answer Type Questions [5M]5 Marks
i. Describe, with the help of a suitable diagram, the working principle of a step-up transformer. Obtain the relation between input and output voltages in terms of the number of turns of primary and secondary windings and the currents in the input and output circuits.
i. Given the input current 15 A and the input voltage of 100 V for a step-up transformer having 90% efficiency, find the output power and the voltage in the secondary if the output current is 3 A.
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Q 26Long Answer Type Questions [5M]5 Marks
a. Derive an expression for the potential energy of an electric dipole in a uniform electric field. Explain conditions for stable and unstable equilibrium.
b. Is the electrostatic potential necessarily zero at a point where the electric field is zero? Give an example to support your answer.
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