Please refer to Class 12 Physics Sample Paper Term 1 With Solutions Set E provided below. The Sample Papers for Class 12 Physics have been prepared based on the latest pattern issued by CBSE. Students should practice these guess papers for class 12 Physics to gain more practice and get better marks in examinations. The Term 1 Sample Papers for Physics Standard 12 will help you to understand the type of questions which can be asked in upcoming examinations.

**Term 1 Sample Paper for Class 12 Physics With Solutions Set **E

**SECTION – A**

**Question 1. If 10 ^{9} electrons move out of a body to another body every second, then what will be the time required to get a total charge of 1 C on the other body?**

**OR**

**Write the expression for the torque 𝜏 acting on a dipole of dipole moment p placed in an electric field E .**

Answer.The charge given out in one second

Answer.

= 1.6 × 10

^{–19}C × 10

^{9}= 1.6 × 10

^{–10}C

Time required to accumulate a charge of 1 C,

**Question 2. What do you mean by Q-value of a nuclear reaction?**

**Answer.**The difference between the rest masses of target nucleus, impinging particle and of product nuclei is called Q-value of nuclear reaction.

**Question 3. Is Ohm’s law universally applicable for all conducting elements? If not, give examples of elements which do not obey Ohm’s law.**

**Answer.**Ohm’s law is not a fundamental law in nature. It is not universally followed. Semiconductor diodes, transistors, thermistors, vacuum tubes etc. do not follow Ohm’s law.

**Question 4. When an ac source is connected across an inductor, show on a graph the nature of variation of the voltage and the current over one complete cycle.****OR****What is the value of impedance of a resonant series LCR circuit?Answer.**V = V

_{0}sinwt

**Question 5. The radius of the innermost electron orbit of a hydrogen atom is 5.3 × 10 ^{–11} m. Calculate its radius in n = 3 orbit.Answer.**

**Question 6. Four point charges each of charge +q is placed on the circumference of a circle of diameter 2d in such a way that they form a square. What will be the potential at the centre?**

**Answer.**Potential at centre due to all charges are

**Question 7. What physical quantity is same for X-rays of wavelength 10 ^{–10} m, red light of wavelength 6800 Å and radio waves of wavelength 500 m?**

**OR**

**The amplitude of the magnetic field part of a harmonic electromagnetic wave in vacuum is B0 = 510 nT.**

**What is the amplitude of the electric field part of the wave?**

Answer.Though they all have different wavelengths and frequencies, but they have same speed i.e., speed of light 3 × 10

Answer.

^{8}m s

^{–1}in vacuum.

OR

**Question 8. In Young’s double slit experiment, what is the nature of the locus of a point P lying in a plane with a constant path difference between the two interfering waves?**

**Answer.**In Young’s double slit experiment, the locus of a point P lying in a plane with a constant path difference between the two interfering waves is a hyperbola.

**Question 9. The incident light has intensity I and the number of electrons emitted per second is N. Then the maximum kinetic energy of emitted electrons per second is K. If the intensity of the incident light is doubled, then what will be the number of electrons emitted per second and the maximum kinetic energy respectively?****OR****In an experiment on photoelectric effect, the slope of the cut-off voltage versus frequency of incident light is found to be 4.12 × 10 ^{–15} V s. Calculate the value of Planck’s constant.**

**Answer.**The maximum kinetic energy of emitted electrons is independent of intensity of incident light and the number of electrons emitted directly proportional to the intensity of incident light.

OR

**Question 10. Predict the direction of induced current in metal rings 1 and 2 when current I in the wire is steadily decreasing ?**

**For question numbers 11, 12, 13 and 14, two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.**

(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 and R is also false**Answer.**When the current I in the wire is steadily decreasing, the direction of induced current in zring 1 will be clockwise and anticlockwise in ring 2 as shown in the figure.

**Question 11. Assertion (A) :** If a conductor is given charge then no excess inner charge appears. **Reason (R) :** Electric field inside conductor is zero.

## Answer

B

**Question 12. Assertion (A) :** A metallic surface is moved in and moved out in a magnetic field, then emf is induced in it. **Reason (R) :** Eddy current will be produced in a metallic surface moving in and out of magnetic field.

## Answer

A

**Question 13. Assertion (A) :** Sharper is the curvature of spot on a charged body lesser will be the surface charge density at that point **Reason (R) :** Electric field is non-zero inside a charged conductor.

## Answer

D

**Question 14. Assertion (A) :** Environmental damage has increased the amount of ozone in the atmosphere. **Reason (R) :** Increase of ozone increases the amount of ultraviolet radiation on earth.

## Answer

D

**SECTION – B**

**Question 15. Group of cells is called a battery. In series grouping of cells their emf ‘s are additive or subtractive while their internal resistances are always additive. Consider a case where, a 20 V battery of internal resistance 1 Ω is connected to three coils of 12 Ω, 6 Ω and 4 Ω in parallel, a resistor of 5 W and a reversed battery (e.m.f. = 8 V and internal resistance 2 Ω) as shown in figure.**

**(i) Calculate the total resistance of the circuit.**

(a) 5 W

(b) 10 W

(c) 15 W

(d) 20 W

## Answer

B

**(ii) Calculate the current in the circuit.**

(a) 1.5 A

(b) 0.5 A

(c) 1.2 A

(d) 1.0 A

## Answer

C

**(iii) The current in the coil of resistance 12 W is**

(a) 0.2 A

(b) 0.1 A

(c) 0.5 A

(d) 1.2 A

## Answer

A

**(iv) Find the potential difference across 20 V battery.**

(a) 0.18 V

(b) 1.88 V

(c) 188 V

(d) 18.8 V

## Answer

D

**(v) Find the potential difference across 8 V battery.**

(a) 0.1 V

(b) 10.4 V

(c) 100 V

(d) 1.88 V

## Answer

B

**Question 16. Two long parallel wires carrying current 2.5 ampere and I ampere in the same direction (directed into the plane of the paper) are held at P and Q respectively, such that they are perpendicular to the plane of the paper. The points P and Q are located at a distance of 5 metres and 2 metres respectively from a collinear point R as shown in figure.**

**(i) Find the net magnetic field at point R.**

(a) 10^{–7} (1 + I)

(b) 10^{–7} (1 – I)

(c) 10^{–7} (1 + 2I)

(d) zero

## Answer

A

**(ii) What will be the direction of net magnetic field at point R.**

(a) along positive y-axis

(b) along positive x-axis

(c) along negative y-axis

(d) along negative x-axis

## Answer

C

**(iii) An electron moving with a velocity of 4 × 105 m s ^{–1} along the positive X-direction experiences a force of magnitude 3.2 × 10^{–20} N at the point R. Find the value of I.**

(a) 0.4 A

(b) 4 A

(c) 5 A

(d) 40 A

## Answer

B

**(iv) Find the positions at which a third long parallel wire carrying a current of magnitude 2.5 ampere directed into the paper may be placed, so that the magnetic induction at R is zero.**

(a) 1 m from R on RX

(b) 2 m from R on PQ

(c) 1 m from R on RQ

(d) 2 m from R on RX

## Answer

A

**(v) Find the position at which a third long parallel wire carrying a current of magnitude 2.5 A which is directed out from the plane of the paper, may be placed, so that the magnetic induction at R is zero.**

(a) 1 m from R on RX

(b) 2 m from R on RQ

(c) 1 m from R on RQ

(d) 2 m from R on RX

## Answer

C

**SECTION – C**

**Question 17. Obtain an expression for the magnetic energy in terms of the magnetic field B, area A and length l of the solenoid having n number of turns per unit length. Also, show that the magnetic energy per unit volume is given by B2/2m0.****OR**

**A rectangular loop and a circular loop are moving out of a uniform magnetic field region with a constant velocity v as shown in the figure. In which loop do you expect the induced emf to be constant during the passage out of the field region? The field is normal to the loops.**

**Answer. **The magnetic energy is,

**OR**

Magnitude of induced emf is directly proportional to the rate of area moving out of the field, for a constant magnetic field,

For the rectangular coil, the rate of area moving out of the field remains same while it is not so for the circular coil. Therefore, the induced emf for the rectangular coil remains constant.

**Question 18. Draw a labelled ray diagram of a compound microscope, showing the formation of image at the near point of the eye.Answer.**

**Question 19. Given a uniform electric field E = 5 ×10 ^{3} i N/C. Find the flux of this field through a square of 10 cm on a side**

**whose plane is parallel to the y-z plane. What would be the flux through the same square if the plane makes a 30° angle with the x-axis?**

Answer.

Answer.

**Question 20. A semiconductor has equal electron and hole concentration of 6 × 108 m ^{3}. On doping with certain impurity, electron concentration increases to 9 × 10^{12}/m^{3}.**

**(i) Identify the new semiconductor obtained after doping.**

**(ii) Calculate the new hole concentration.**

**Answer.**(i) n-type

**Question 21. You are given two nuclides ^{7}_{3}X and ^{4}_{3}Y.**

**(i) Are they the isotopes of the same element?**

**(ii) Which one of the two is likely to be more stable? Give reason.**

**OR**

**Draw a plot of potential energy of a pair of nucleons as a function of their separation. Write two important**

**conclusions which you can draw regarding the nature of nuclear forces.**

**Answer.**(i) Yes, they are the isotopes of the same element because they have same atomic number (Z = 3).

(ii) The isotope

^{7}

_{3}X has 3 protons and 4 neutrons while the isotope

^{4}

_{3}Y has 3 protons and 1 neutron.

Due to the presence of a greater number of neutrons in

^{7}

_{3}X, the strong attractive nuclear force dominates over the electrostatic repulsion between the protons.

So

^{7}

_{3}X is more stable than

^{4}

_{3}Y.

**OR**

Plot of potential energy of a pair of nucleons as a function of their separation is given in the figure.

Conclusions : (i) The nuclear force is much stronger than the coulomb force acting between charges or the gravitational forces between masses.

(ii) The nuclear force between two nucleons falls rapidly to zero as their distance is more than a few fermies.

(iii) For a separation greater than r0, the force is attractive and for separation less than r0, the force is strongly repulsive.

**Question 22. A proton and an a-particle are accelerated, using the same potential difference. How are the de Broglie wavelengths λ _{p} and λ_{α} related to each other?**

**Answer.**We know that,

**Question 23. Compare the conductivity of semiconductor at absolute zero temperature and at room temperature.Answer.**

At absolute zero temperature (0 K) conduction band of semiconductor is completely empty, i.e., s = 0.

Hence the semiconductor behaves as an insulator. At room temperature, some valence electrons acquire enough thermal energy and jump to the conduction band where they are free to conduct electricity. Thus the semiconductor acquires a small conductivity at room temperature.

**Question 24. A radio can tune in to any station in the 7.5 MHz to 12 MHz band. What is the corresponding wavelength band?**

**Answer.**Maximum wavelength in the band is for lowest frequency

So, the wavelength band for tuning is between 25 m to 40 m.

**Question 25. Derive the expression for the torque acting on an electric dipole, when it is held in a uniform electric field.****Identify the orientation of the dipole in the electric field, in which it attains a stable equilibrium.****OR****Define electric flux. Write its S.I. unit.****“Gauss’s law in electrostatics is true for any closed surface, no matter what its shape or size is”. Justify this statement with the help of a suitable example.Answer. **Torque on a dipole in uniform electric field: When electric dipole is placed in a uniform electric field, its two charges experience equal and opposite forces, which cancel each other and hence net force on an electric dipole in a uniform electric field is zero.

However these forces are not collinear, so they give rise to some torque on the dipole given by

Torque = Magnitude of either force × Perpendicular distance between them

**SECTION – D**

**Question 26. Show that average value of radiant flux density ‘S’ over a single period ‘T’ is given by**

**OR****Show that the radiation pressure exerted by an EM wave of intensity I on a surface kept in vacuum is I/c.Answer.**

**Question 27. A particle of mass m and charge (–q) enters the region between the two charged plates initially moving along X-axis with speed v _{x} as shown in the given figure.**

**The length of plate is L and an uniform electric field E is maintained between the plates. Show that the vertical deflection of the particle at the far edge of the plate is**

**Answer.**Let a particle of mass m, charge –q enter normally the region between two charged plates, each of length L, as shown in the figure. Uniform electric field E between the plates is along Y-axis and initial velocity of particle vx is along X-axis.

**Question 28. The horizontal component, of the earth’s magnetic field at a place is 1/√3 times its vertical component. Find the value of the angle of dip at that place. What is the ratio of the horizontal component to the total magnetic field of the earth at that place?Answer.**Let the horizontal component of the earth’s

magnetic field be H

_{E}and vertical component be Z

_{E}

**Question 29. An equiconvex lens with radii of curvature of magnitude R each, is put over a liquid layer poured on top of a plane mirror. A small needle, with its tip on the principal axis of the lens, is moved along the axis until its inverted real image coincides with the needle itself. The distance of the needle from the lens is measured to be a. On removing the liquid layer and repeating the experiment the distance is found to be b.**

**Given that two values of distances measured represent the focal length values in the two cases, obtain a formula for the refractive index of the liquid.Answer.**Clearly, equivalent focal length of equiconvex lens

and water lens f = a

Focal length of equiconvex lens, f

_{1}= b

Focal length f

_{2}of water lens is given by

**Question 30. With the help of a suitable diagram, explain the formation of depletion region in a p-n junction. How does its width change when the junction is (i) forward biased, and (ii) reverse biased ?****OR****Assuming the ideal diode, draw the output waveform for the circuit given in figure. Explain the waveform.**

**Answer.**

When p-n junction is formed, then at the junction,free electrons from n-type diffuse over to p-type, and hole from p-type over to n-type. Due to this a layer of positive charge is built on n-side and a layer of negative charge is built on p-side of the p-n junction.

This layer sufficiently grows up within a very short time of the junction being formed, preventing any further movement of charge carriers (electrons and holes) across the p-n junction.

This space – charge region, developed on either side of the junction is known as depletion region as the electrons and holes taking part in the initial movement across the junction deplete this region of its free charges.

Width of depletion region layer

(i) decreases when the junction is forward biased and

(ii) increases when it is reverse biased.**OR**

For the voltage less than 5 V, the diode is reverse biased and circuit will act as open circuit.

When input voltage is greater than 5 V, diode is in conducting state.

**SECTION – E**

**Question 31. (a) In a series LCR circuit connected to an ac source of variable frequency and voltage V = V _{m} sinwt,draw a plot showing the variation of current (I) with angular frequency (w) for two different values of resistance R_{1} and R_{2}(R_{1} > R_{2}).**

**(b) Write the condition under which the phenomenon of resonance occurs. For which value of the resistance out of the two curves, a sharper resonance is produced?**

**(c) Define Q-factor of the circuit and give its significance.**

**OR**

**A device ‘X’ is connected to an ac source V = V**

_{0}sin wt. The variation of voltage, current and power in one cycle is shown in the following graph :**(a) Identify the device ‘X’.****(b) Which of the curves A, B and C represent the voltage, current and the power consumed in the circuit?****Justify your answer.****(c) How does its impedance vary with frequency of the ac source? Show graphically.****(d) Obtain an expression for the current in the circuit and its phase relation with ac voltage.**

**Answer.**(a) Figure shows the variation of i

_{m}with w in a LCR series circuit for two values of resistance R

_{1}and R

_{2}(R

_{1}> R

_{2}),

The Q factor determines the sharpness at resonance as for higher value of Q factor the tuning of the circuit and its sensitivity to accept resonating frequency signals becomes much higher.

OR

(a) Device X is a capacitor.

(b) B → Voltage (Because it is sine wave)

C → Current (Because current leads voltage by p/2)

A → Power (Average power over one cycle is zero)

**Question 32. (a) A ray of light passing from air through an equilateral glass prism undergoes minimum deviation when the angle of incidence is 3/4 of the angle of prism. Calculate the speed of light in the prism.****(b) The figure shows a ray of light falling normally on the face AB of an equilateral glass prism having refractive index 3/2, placed in water of refractive index 4/3. Will this ray suffer total internal reflection on striking the face AC? Justify your answer.**

**OR****(a) Light from a point source in air falls on a convex spherical glass surface of refractive index 1.5 and radius of curvature 20 cm. The distance of light source from the glass surface is 100 cm. At what position is the image formed ?****(b) A convex lens made up of glass of refractive index 1.5 is dipped, in turn, in (I) a medium of refractive index 1.65, (II) a medium of refractive index 1.33.****(i) Will it behave as a converging or a diverging lens in the two cases?****(ii) How will its focal length change in the two media?Answer.** (a) For equilateral prism A = 60°

For minimum angle of deviation,

On face AC, angle of incidence is less than that of critical angle, so there will be no total internal reflection.**OR**

**Question 33. (a) Using de Broglie’s hypothesis, explain with the help of a suitable diagram, Bohr’s second postulate of quantization of energy levels in a hydrogen atom.****(b) The ground state energy of hydrogen atom is –13.6 eV. What are the kinetic and potential energies of the electron in this state?****OR****Using Bohr’s postulates, obtain the expression for the total energy of the electron in the stationary states of the hydrogen atom. Hence draw the energy level diagram showing how the line spectra corresponding to Balmer series occur due to transition between energy levels.Answer. **(a) According to de Broglie, a stationary orbit is that which contains an integral number of de Broglie waves associated with the revolving electron.

For an electron revolving in nth circular orbit of radius r

_{n},

Total distance covered = Circumference of the orbit = 2pr

_{n}

**OR**

(i) According to Bohr’s postulates, in a hydrogen atom, as single electron revolves around a nucleus of charge +e. For an electron moving with a uniform speed in a circular orbit of a given radius, the centripetal force is provided by coulomb force of attraction between the electron and the nucleus. The gravitational attraction may be neglected as the mass of electron and proton is very small.

When the electron in a hydrogen atom jumps from higher energy level to the lower energy level, the difference of energies of the two energy levels is emitted as a radiation of particular wavelength. It is called a spectral line.

(ii) In H-atom, when an electron jumps from the orbit n_{i} to orbit n_{f} , the wavelength of the emitted radiation is given by