# HBSE Class 12th Physics Solved Question Paper 2019

HBSE Class 12th Physics Solved Question Paper 2019

HBSE Class 12 Physics Previous Year Question Paper with Answer. HBSE Board Solved Question Paper Class 12 Physics 2019. HBSE 12th Question Paper Download 2019. HBSE Class 12 Physics Paper Solution 2019. Haryana Board Class 12th Physics Question Paper 2019 Pdf Download with Answer.

SET-A

Q1.(i) Process of sharing the charges with the earth is called as ……………

Ans. Grounding or Earthing

(ii) SI unit of ∈⁰ (permitivity of free space) is :

(A) C-²N¹m-²

(B) C²N-¹m-²

(C) N¹C²m-²

(D) N-¹C²m²

Ans. (B) C²N-¹m-²

(iii) Write the expression for energy density of electric field ‘E’ in free space.

Ans. ½∈⁰E²

(iv) With the increase of temperature, the resistivity of a semiconductor :

(A) Decreases

(B) increases

(C) May increase or decrease

(D) Does not change

Ans. (A) Decreases

(v) How much current flows through a 2kΩ resistor when a potential difference of 4V is applied across its ends ?

Ans. Current, I = V/R = 4V/2kΩ = 4/2×10-³ = 2×10-³ A = 2 mA

(vi) What is the value of relative magnetic permeability of perfectly diamagnetic substance ?

Ans. Zero

(vii) The power factor for a purely capacitive circuit is :

(A) 1

(B) √2

(C) 1/√2

(D) Zero

Ans. (D) Zero

(viii) Which electromagnetic wave are used in cellular phones to transmit voice communication in the Ultra High Frequency (UHF) band ?

(ix) Who discovered the nucleus ?

(A) Thomson

(B) Bohr

(C) Rutherford

(D) de Broglie

Ans. (C) Rutherford

(x) What is SI unit of activity of Radioactive Substance ?

Ans. Becquerel or Bq

(xi) Rainbow is a phenomenon due to :

(A) Reflection

(B) Refraction

(C) Dispersion

(D) All of these

Ans. (D) All of these

(xii) What is the shape of wavefront for the light diverging from a point source ?

Ans. Spherical Wavefront

(xiii) Name the optoelectronic device used to detect optical signals.

Ans. Photo Detector

(xiv) In an electronic communication system, what is Attenuation ?

Ans. The loss of strength of a signal while propagating through a medium is called as Attenuation.

Q2. Three capacitors of capacitances 2 pF, 3 pF and 4 pF are connected in parallel. Determine the charge on each capacitor, if the combination is connected to a 100 V supply ?

Ans. Q = CV

Q1 = C1V = 2pF × 100 V = 2 × 10-¹⁰ coulomb

Q2 = C2V = 3pF × 100 V = 3 × 10-¹⁰ coulomb

Q3 = C3V = 4pF × 100 V = 4 × 10-¹⁰ coulomb

Q3. What is Kirchhoff’s loop rule ?

Ans. Kirchoff’s loop sale states that the algebric sum of changes in potential around a closed loop involving resistors and cells in the loop is zero.

Q4. Name four applications of Eddy currents.

Ans. Applications of Eddy currents-

(i) Magnetic breaking in trains

(ii) Electromagnetic damping

(iii) induction furnace

(iv) Electric power meters

Q5. State Faraday’s Law of Electromagnetic Induction.

Ans. When magnetic flux linked with coil changes, e.m.f is induced.

e.m.f. induced is equal to negative rate of change in Magnetic flux

Q6. A radio can tune into any station in the 7.5 MHz to 12 MHz band. What is corresponding wavelength band ?

Ans. Wavelength (λ) = C/v

λ1 = (3×10⁸m/s) ÷ (7.5×10⁶ Hz) = 40 m

λ= (3×10⁸m/s) ÷ (12×10⁶ Hz) = 25 m

So, corresponding wavelength band is 40 m to 25 m.

Q7. What is de Broglie wavelength of a bullet of mass 0.040 kg travelling at a speed of 1.0 km/sec ?

Ans. Broglie wavelength (λ) = h/mv = (6.6×10-³⁴) ÷ (0.040×1.0×10³m/s) = 1.6 × 10-³⁵ m

Q8. What is basic nuclear process underlying β- decay ? Write nuclear reaction of this decay for ²¹⁰Bi83.

Ans. Basic nuclear process in β- decay is

n → p + e- + v

²¹⁰Bi83 → ²¹⁰P84 + e- + v

Q9. Draw the I-V characteristics of a Zener diode. Also sketch the circuit diagram of Zener diode as a voltage regulator.

Ans. I-V Characteristics of Zener diode–

Zener diode as a Voltage Regulator–

Q10. Write the truth table for given circuit.

Ans. Truth table is

Q11. Draw Block diagram of Communication System.

Ans.

Q12. Discuss three basic postulates of Bohr’s model of atom.

Ans. Basic postulates of Bohr’s model of atom-

(i) In an atom, the electrons revolve around the nucleus in certain definite circular paths called orbits, or shells.

(ii) Each shell or orbit corresponds to a definite energy. Therefore, these circular orbits are also known as energy levels or energy shells.

(iii) The orbits or energy levels are characterized by an integer not, where, n can have values 1, 2, 3, 4……. The integer not (= 1, 2, 3…) is called the quantum number of respective orbit. The orbits are numbered as 1, 2, 3, 4………… etc., starting from the nucleus side. Thus, the orbit for which n=1 is the lowest energy level.

Q13. What is photoelectric effect ? Discuss the effect of intensity of light on photoelectric current.

Ans. The photoelectric effect refers to the emission, or ejection of electrons from the surface of a metal in response to incident light. This takes place because of the energy of incident photons of light have energy more than the work potential of the metal surface, ejecting electrons with positive kinetic energy. These electrons are used as the current and it is known as photo electric current.

Intensity has nothing to do with the energy of the photon. Therefore, the intensity of the radiation is increased, the rate of emission increases but there will be no change in the kinetic energy of electrons. With an increasing number of emitted electrons, the value of the photoelectric current increases.

Q14. What is polarization by reflection ? Deduce Brewster Law ?

Ans. Polarization by reflection– When light shines at a certain angle, it is possible for the reflected light to become completely polarized. This phenomenon is called polarization by reflection. It is the plane of polarisation parallel to the plane of the interface.

Polarization by Brewster’s law– Brewster’s angle is an angle of incidence at which light with a particular polarization is perfectly transmitted through a transparent dielectric surface with no reflection. When unpolarized light is incident at this angle, the light that is reflected from the surface is therefore perfectly polarized. A glass plate or a stack of plates placed in a light beam at Brewster’s angle can thus be used as a polarizer.

Q15. A series L-C-R circuit with R = 44 Ω, C = 8 µF and L = 50 H is connected to a variable frequency 220 V ac supply. Calculate angular frequency, impedance and current at resonance condition.

Ans. ω = √1/LC = √1/50H×8µF = 50 Hz

Current at resonance;  I = V/R = 220V/44Ω = 5A

Z = R =  44 Ω

I = V/Z = V/R

Z = √R²+(XL-XC)² ;  X= X

so, Z = R = 44 Ω

Q16. Define ampere circuital law ? Write expression for magnetic field at a distance r from a straight infinite wire carrying current I. Which rule is used to determine the direction of this magnetic field ?

Ans. Ampere’s Circuital Law states the relationship between the current and the magnetic field created by it. This law states that the integral. Ampere’s circuital law states that line integral of the magnetic field forming a closed loop around the current (I) carrying wire, in the plane normal to the current, is equal to the μ times the net current passing through the close loop.

Biot Savart law states that If there is a current carrying wire and a point P close to it, then the intensity of the magnetic field produced at that point, due to a very small part of the wire is given by

dB= μ/4π × IdLsinθ/r²

B = ∫dB = μ/4π × I(2πr)/r² = μI/2r

The direction of the magnetic field can be determined by Fleming’s right-hand rule. According to this rule, if a straight wire conductor is held in the right hand such that the thumb indicates the direction of the current, then the direction in which the fingers encircle around will indicate the direction of the magnetic field.

Q17. Explain the principle of Potentiometer. Draw the labelled circuit diagram for comparing of emf of two cells ?

Ans. We know that a potentiometer is used to determine the internal resistance of a cell. Besides this, we will have a determination of potential difference using a potentiometer.

Principle : The basic working principle of this is based on the fact that the fall of the potential across any portion of the wire is directly proportional to the length of the wire, provided wire has a uniform cross-sectional area and the constant current flowing through it.

A potentiometer basically works on the principle of varying the resistance of a fixed resistor by moving the sliding/rotary contact or the wiper. By displacing the position of the wiper, the length of the resistive wire is altered. This change in the length of the wire is proportional to the change in the resistance offered to the circuit. In a potentiometer, input is applied across the fixed terminals, whereas the output is noted between the movable and a fixed terminal.

E1/E2 = L1/L2

Q18. Find expression for electric field intensity due to a uniformly charged thin spherical shell at a point outside the shell.

Ans. Let P be the point outside the shell at a distance r from the centre. Since the surface of the sphere is spherically symmetric, the charge is distributed uniformly throughout the surface.

A spherical Gaussian surface with the radius r and total charge enclosed on this Gaussian surface Q is selected. If Q > 0, then the electric field is radially pointed outward and if Q < 0, then the electric field is radially pointed inward.

From Gauss law, we know that

∫E.dA = Q/ε

E.4πr² = Q/ε

E = 1/4πε × Q/r²

We can say that the electric field at a point outside the shell will remain the same if the entire charge Q is concentrated at the centre of the spherical shell.

Q19. Explain the magnetic hysteresis loop ? What are its uses ?

Ans. The hysteresis loop shows the relationship between the magnetic flux density and the magnetizing field strength. The loop is generated by measuring the magnetic flux coming out from the ferromagnetic substance while changing the external magnetizing field.

Uses–

(i) Several applications of hysteresis are found in ferromagnets. It is mostly used to retain a memory, for example, hard disks, magnetic tape, and credit cards.

(ii) Hysteresis is applied in many artificial systems such as in thermostats and Schmitt triggers which are designed to prevent unwanted frequent or unwanted rapid switching.

(iii) A hysteresis is sometimes intentionally made part to computer algorithms.

(iv) Hysteresis can be observed when decreasing the angle of attack of a wing after stall, regarding the lift and drag coefficients.

OR

Explain the principle of moving coil galvanometer ? How it can be converted to an ammeter ?

Ans. Moving Coil Galvanometer– A moving coil galvanometer is an instrument which is used to measure electric currents. It is a sensitive electromagnetic device which can measure low currents even of the order of a few microamperes.

Principle– When a current flows through the coil, a torque acts on it. The magnetic torque tends to rotate the coil. Spring provides a counter torque that balances the magnetic torque resulting in a steady angular deflection.

Convert Galvanometer to Ammeter– A galvanometer is converted into an ammeter by connecting it in parallel with a low resistance called shunt resistance. Suitable shunt resistance is chosen depending on the range of the ammeter.

Q20. Draw a labelled ray diagram showing the image formation in an astronomical telescope. Define its magnifying power and write expression for it.

Ans. Astronomical Telescope– Astronomical Telescope is used to observe objects which are very far from us. Telescopes produce magnified images of distant objects. It produces virtual and﻿ inverted image and is used to see heavenly bodies like﻿ sun, stars, planets etc. so the inverted image does not﻿ affect the observation.﻿

Principle– It is based on the principle that when rays﻿ of light are made to incident on an objective from a﻿ distant object, the objective forms the real and inverted﻿ image at its focal plane. The eye lens is so adjusted that﻿ the final image is formed at least distance of distinct﻿ vision.﻿

Construction– The refracting type astronomical﻿ telescope consists of two convex lenses one of which is﻿ called the objective and the other eye piece. The objective﻿ is a convex lens of large focal length and large aperture. It is generally a combination of two lenses in contact so﻿ as to reduce spherical and chromatic aberrations. The﻿ eye piece is also a convex lens but of short focal length﻿ and small aperture. The objective is mounted at one end﻿ of a brass tube and the eye piece at the other end in a﻿ smaller tube which can slide inside the bigger tube﻿ carrying the objective.

Magnifying Power– The magnifying power of a refracting type astronomical telescope is defined as the ratio of angle subtended by the final image at eye to the angle subtended by the object at eye.

M= fo/fe (1 + fe/D)

OR

Find out the expression for Fringe width in Young’s double slit experiment.

Ans.

Q21. Draw a circuit diagram to study characteristics of n-p-n transistor in CE configuration. Draw the sketch of input and output characteristics of this configuration. Define current amplification factor ?

Ans.

OR

Draw the symbol of a p-n-p transistor. Show the biasing of a p-n-p transistor and explain the transistor action.

Ans.

SET-B

Q1.(i) Electric wiring in our homes has three wires : live, neutral and ……….

Ans. Earth

(ii) SI unit of k (proportionality constant in coulomb’s law) is :

(A) N¹C-²m²

(B) N-¹C²m-²

(C) N¹C²m-²

(D) N-¹C-²m²

Ans. (A) N¹C-²m²

(iii) Write the expression for energy stored in a capacitor in terms of capacitance and potential difference between its plates.

Ans. ½CV²

(iv) With the increase in length of a conductor, its resistivity :

(A) Increases

(B) Decreases

(C) May increase or decrease

(D) Does not change

Ans. (D) Does not change

(v)How much current flows through a 4 kΩ resistor when a potential difference of 2 V is applied across its ends ?

Ans. Current, I = V/R = 2V/4kΩ = 2/4×10³ = 0.5 × 10-³ = 0.5 mA

(vi) What is the value of magnetic susceptibility of a perfectly diamagnetic substance ?

Ans. -1

(vii) Phase difference between voltage and current when an ac source is connected to an inductor :

(A) 0°

(B) 90°

(C) 45°

(D) 180°

Ans. (B) 90°

(viii) Which electromagnetic wave is used to kill germs in water purifiers ?

Ans. Ultra-Violet (UV) Rays

(ix) According to Rutherford’s experiments, the size of nucleus is about :

(A) 10-¹¹m to 10-¹⁰m

(B) 10-¹³m to 10-¹²m

(C) 10-¹⁵m to 10-¹⁴m

(D) 10-¹²m to 10-¹¹m

Ans. (C) 10-¹⁵m to 10-¹⁴m

(x) Who discovered neutron ?

(xi) Optical fibres works on the phenomenon of :

(A) Dispersion

(B) Refraction

(C) Scattering

(D) Total Internal Reflection

Ans. (D) Total Internal Reflection

(xii) What is the shape of wavefront of the light emerging out of a convex lens when a point source is placed at its focus ?

Ans. Plane Wavefront

(xiii) Name the optoelectronic device which convert optical radiation into electricity ?

Ans. Solar Cells or Photoelectric Cells

(xiv) What is ‘Range’ in an electronic communication system ?

Ans. Range is the largest distance between a source and a destination up to which the signal is received with sufficient strength.

SET-C

Q1.(i) Quantization of charge was experimentally demonstrated by ……… in 1912.

Ans. Milikan

(ii) Ratio of magnitudes of electric force in air and water between an electron and proton is :

(A) K (dielectric constant)

(B) 1/K

(C) 1

(D) 0

Ans. (A) K (dielectric constant)

(iii) Write the expression for energy stored in a capacitor in terms of charge and potential difference between its plates.

Ans. ½QV

(iv) With the increase of temperature, the resistivity of a metal :

(A) increases

(B) Decreases

(C) May increase or decrease

(D) Does not change

Ans. (A) increases

(v) How much current flows through a 3kΩ resistor when a potential difference of 9V is applied across its ends ?

Ans. Current, I = V/R = 9V/3kΩ = 9/3×10³ = 3×10-³ A = 3mA

(vi) What is the value of magnetic permeability of a perfectly diamagnetic substance ?

Ans. Zero

(vii) The power factor for a purely inductive ac circuit is :

(A) 1

(B) Zero

(C) 1/√2

(D) √2

Ans. (B) Zero

(viii) Which electromagnetic wave is used in remote switches of TV sets ?

Ans. infrared Rays

(ix) Which model of atom suggests that atom is a spherical cloud of positive charges with electrons embedded in it ?

(A) Rutherford model

(B) Bohr model

(C) Thomson model

(D) de Broglie

Ans. (C) Thomson model

Ans. AH Becquerel

(xi) Phenomenon of splitting of light into its constituent colours is known as :

(A) Scattering

(B) Diffraction

(C) Refraction

(D) Dispersion

Ans. (D) Dispersion

(xii) What is the shape of portion of wavefront of light from a distant star intercepted by earth ?

Ans. Plane Wavefront

(xiii) Name the optoelectronic device that convert electrical energy into light ?

Ans. LED (Light Emitting Diode)

(xiv) In an electronic communication system, define Modulation ?

Ans. Process of superimposition of low frequencies on high frequency carrier waves is known as modulation.

SET-D

Q1.(i) There are about ……….. electrons in a charge of -1 coulomb.

Ans. 6 × 10¹⁸

(ii) Nature of electric force between two protons is :

(A) Attractive

(B) Neutral

(C) Repulsive

(D) None of the above

Ans. (C) Repulsive

(iii) Write the expression for energy stored in a capacitor in terms of charge and capacitance ?

Ans. ½Q²/C

(iv) With the increase of area of cross-section of a conductor, its resistivity :

(A) Increases

(B) Decreases

(C) May increase or decrease

(D) Does not change

Ans. (D) Does not change

(v) How much current flows through a 5kΩ resistor when a potential difference of 5V is applied across its ends ?

Ans. Current, I = V/R = 5V/5kΩ = 5/5×10³ = 1×10-³ = 1mA

(vi) What is the relative magnetic permeability of a substance whose magnetic susceptibility   is -1 ?

Ans. Zero

(vii) Which electromagnetic radiation is used in medicine to destroy cancer cells ?

Ans. Gamma Rays

(viii) Whose model of atom is also called nuclear model of atom ?

(A) Thomson

(B) Rutherford

(C) de Broglie

(D) Bohr

Ans. (B) Rutherford

(ix) Phase difference between voltage and current when an ac source is connected to a capacitor :

(A) 90°

(B) 45°

(C) 180°

(D) 0°

Ans. (A) 90°

(x) 1 Decay per second are equivalent to what unit of radioactivity ?

Ans. Becquerel or Bq

(xi) Sky seems blue due to which phenomenon of light :

(A) Dispersion

(B) Diffraction

(C) Scattering

(D) Refraction

Ans. (C) Scattering

(xii) What is shape of a wavefront around a straight line source ?

Ans. Cylindrical Wavefront

(xiii) Name a semiconductor device which can be used as a voltage regulator ?

Ans. Zener Diode

(xiv) What a receiver does in an electronic communication system ?

Ans. A receiver extracts the desired message signals from the received signals at the channel output.

Other Questions (Coming Soon…)

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