Class- XII

                                                                                               Sample paper - 1

 

General Instructions:                                                                                                                                       Durations: 3 hrs

1. All questions are compulsory. There are 37 questions in all.
2. This question paper has 4 sections: Section-A, Section-B, Section-C & Section-D.
3. Section A contains 20 questions of one mark.
4. Section-B contain 7 questions of 2 marks.
5. Section-C contains 7 questions of 3 marks
6. Section- D contains 3 questions of 5 marks each.
7. There is no overall choice. However internal choices are provided. You have to attempt only one of the choices in such questions.
8. Use of calculators is not permitted. However, you may use log tables if necessary.

 

SECTION - A

Question 1:

If the net electric flux through a closed surface is 0, then:

(a) no net charge is enclosed by the surface.

(b) uniform electric field exists within the surface.

(c) electric potential varies from point to point inside the surface.

(d) charge is present inside the surface.

 

Question 2:                                                                                                                          

If the wire is stretched to make its length 4 times, then its specific resistance will be:

(a) sixteen times

(b) uncharged

(c) four times

(d) 1/4^th

 

Question 3:

Which option is not correct about Kirchhoff’s 2^nd Law?

(a) It can be applied to closed circuits as well as open circuit.

(b) It is also known as mesh law, loop law, or voltage law.

(c) It is law of conservation of energy.

(d) It can be applied to closed circuits.

 

Question 4:                                                                                                                          

Why is the use of potentiometer preferred over that of a voltmeter for measurement of e.m.f of a cell?

(a) Potentiometer is of small size

    (b) Because of null method

(c) Both (a) & (b)

(d) None

 

Question 5:

Two parallel wires in free space are 10cm apart and each carries a current of 10 A in the same direction. The force exerted by one wire on the other (per metre length) is

 

Question 6:

A resistor of 200 Ω and a capacitor of 15.0 µF are connected in series to a 220 V, 50 Hz ac source. Calculate the current in the circuit?

OR

For circuits used for transporting electric power, a low power factor implies large power loss in transmission. Explain.

 

Question 7:                                                                                                                          

At which temperature would an intrinsic semiconductor behave like a perfect insulator?

 

Question 8:

Prove the average energy density of the oscillating electric field is equal to that of the oscillating magnetic field.

 

Question 9:

Why cannot be used Si and Ge in fabrication of visible LEDs?

OR

In a p-n junction diode, the forward bais resistance is low as compared to the reverse bias resistance. Give reason.

 

Question 10: 

Define the "threshhold frequency" in the context of photoelectric emission.

 

Question 11:

Can Huygens’s theory explain the photoelectric effect?

 

Question 12:

What is the maximum number of spectral lines emitted by a hydrogen atom when it is in the third excited state?

OR

What are the drawbacks of the Thomson’s model of atom?

 

Question 13:

Two particles have equal momenta. What is the ratio of their de-Broglie wavelength?

 

Question 14:

Two metals A & B have work function 4 eV and 10 eV respectively. Which metal has higher threshold wavelength?

 

Question 15:                                                                                                                          

What do you mean by binding energy per nucleon?

 

Directions: For questions 16 to 20, there are questions of Assertion (A) and Reason (R). Select the correct answer to these questions from the code (a), (b), (c), (d)

(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 correct explanation of A

(c) A is true and R is false

(d) A is false and R is true

 

Question 16:                                                                                                                         

Assertion (A): Nuclear force is same between neutron-neutron, proton-proton and neutron-proton.

Reason (R): Nuclear force is charge independent

 

Question 17:                                                                                                                         

Assertion (A): When a p-n junction diode is reverse biased, a feeble reverse current flow known as reverse saturation current.

Reason (R): In reverse bias condition, the minority carries can cross the junction.

 

Question 18:

Assertion (A): de- Broglie equation is significant for microscopic particles.

Reason (R): de- Broglie wavelength inversely proportional to the mass of a particle when velocity is kept constant.

 

Question 19:      

Assertion (A): A double convex air bubble is formed within a glass slab. the air bubble behanves like a converging lens.       

Reason (R): Refractive Index of glass is more than that of the refractive index of air.

 

Question 20:

Assertion (A): Gamma rays are electromagnetic waves having smaller wavelength.

Reason (R): Gamma rays are having the lowest frequency.

 

Section - B

Question 21:                                                                                                                         

Identify the electromagnetic waves whose wavelength varies from:

(a) 10^-12 m < λ < 10^-8 m

     (b) 10^-3 m < λ < 10^-1 m

Write one use of each.

 

Question 22:                                                                                                                         

An equilateral glass prism has a refractive index is 1.6 in air. Calculate the angle of the minimum deviation of the prism, when kept in a medium of refractive index 4 .

 

Question 23:                                                                                                                         

Define secondary wavelets and how can we construct new wavefront with them?

 

Question 24:                                                                                                                         

If the frequency of light is incident on the cathode of a photocell is increased, how will following be affected? Justify your answer.

(1) Energy of the photo electrons

(2) Photo current

 

Question 25:                                                                                                                         

Calculate the orbital period of the electron in the 1^st excited state of hydrogen atom.

OR

Draw the energy band diagram when intrinsic semiconductor (Ge) is doped with impurity atoms of Antimony (Sb). Name the extrinsic Semiconductor so obtained and majority charge carriers in it.

 

Question 26:                                                                                                                         

(a) Why is a photodiode operated under reverse bias condition?

(b) Draw V-I characteristics curves of photodiode for incident light of intensities I₁ and I₂ (I₁>I₂). 

 

Question 27:                                                                                                                         

A parallel beam of light 500 nm falls on a narrow slit and the resulting diffraction pattern is observed on screen 1 m away. It is observed that the first minima are at a distance of 2.5 mm from the centre of the screen. Calculate the width of the slit.

 

Section - C

Question 28:                                                                                                                         

(a) State two features of Einstein’s photoelectric equation.

(b) Radiation of frequency 10¹⁵ Hz is incident on two photosensitive surfaces P & Q. There is no photoemission from surface P. Photoemission occurs from surface Q but photoelectrons have zero kinetic energy. Explain these observations and find the value of work function for surface Q.

 

Question 29:                                                                                                                         

Explain the information of potential barrier and depletion region in a p-n junction diode. What is effect of applying forward bias on the width of depletion region?

OR

In a metre bridge experiment null point is obtained at 20 cm from the end of the wire when resistance X is balanced against another resistance Y. If X<Y, then where will be the new position of the null point from the same end, if one decides to balance a resistance of 4 X against Y.

 

Question 30:

A long straight wire AB carries a current of 4A. A proton P travels at 4×10⁶ m/s, parallel to the wire, 0.2 m from it and in a direction opposite to the current as shown in figure. Calculate the force with the magnetic field of current exerts on the proton.

 

Question 31:                                                                                                                          

The earth’s magnetic field at a certain place has a horizontal component of 0.3 G and total strength 0.5 G. Find the dip in tan^-1?

 

Question 32:                                                                                                                         

A radio can tune over the frequency range of a portion of MW broadcast band: 800 kHz to 1200 KHz. If its LC circuit has an effective inductance of 200µH, what must be the range of its variable capacitor.

 

Question 33:                                                                                                                    

A ray of light incident on the face AB of an isosceles triangular prism makes an angle of incidence (i) and deviates by angle   as shown in the figure. Show that in the position of minimum deviation     Also find out the condition when the refracted ray QR suffers total internal reflection.

 

Question 34:                                                                                                                         

Write any 2 distinguishing features between insulators, conductors and semiconductors on the basis of their band diagrams.

 

Section - D

Question 35:                                                                                                                        

(a) A short bar magnet placed with its axis at 30^∘ with a uniform external magnetic field of 0.25T experiences a torque of magnitude equal to 4.5 x 10^-2 J.  What is the magnitude of magnetic moment of the magnet?

(b) A closely wound solenoid of 800 turns and area of cross section 2.5×10⁻⁴m² carries a current of 3.0A. Explain the sense in which the solenoid acts like a bar magnet. What is its associated magnetic moment?

 

Question 36:                                                                                                                       

A tank is filled with water to a height of 12.5 cm. The apparent depth of a needle lying at the bottom of the tank is measured by a microscope to be 9.4 cm. What is the refractive index of water? If water is replaced by a liquid of refractive index 1.63 upto the same height, by what distance would be microscope have to be moved to focus on the needle again?

 

Question 37:                                                                                                              

(a) At room temperature (27^oC) the resistance of a heating element is 100 Ω. What is the temperature of the element if the resistance is found to be 117 Ω, given that the temperature coefficient of the material of the resistor is 1.70 × 10^–4 °C^–1.

(b) In a potentiometer arrangement, a cell of emf 1.25 V gives a balance point of 35 cm length of the wire. If the cell is replaced by another cell and the balance point shift to 63 cm, what is the emf of the second cell?

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