­Class – XII

Sample Paper - 1

General Instructions:

Read the following instructions very carefully and strictly follow them:

(i) This question paper comprises four Sections – A, B, C and D.

(ii) There are 37 questions in the question paper. All questions are compulsory.

(iii) Section A – Questions no. 1 to 20 are very short answer type questions, carrying one mark each.

(iv) Section B – Questions no. 21 to 27 are short answer type questions, carrying two marks each.

(v) Section C – Questions no. 28 to 34 are long answer type questions, carrying three marks each.

(vi) Section D – Questions no. 35 to 37 are also long answer type questions, carrying five marks each.

(vii) There is no overall choice in the question paper.

(viii) In addition to this, separate instructions are given with each section and

question, wherever necessary.

(ix) Use of calculators and log tables is not permitted.

(x) You may use the following values of physical constants wherever necessary.

Mass of neutron = 1.675 × 10⁻²⁷ kg

Mass of proton = 1.673 × 10²⁷ kg

Avogadro’s number = 6.023 × 10²³ per gram mole

Boltzmann constant = 1.38 × 10⁻²³ JK^-1

 

Section - A

Question 1:

LED lights of chargers glow even after it is switched off. Which of the following causes this situation?
(a) LC Oscillations
(b) phasors
(c) power of the AC circuit
(d) eddy currents

 

Question 2:

Electric field is a _______

(a) scalar quantity

(b) vector quantity

(c) tensor quantity

(d) quantity that has properties of both scalar and vector

 

Question 3:

Which of the following is not a point of similarity between Biot-Savart law and Coulomb’s law?

(a) both fields depend inversely on the square of the distance from the source to the point of observation

(b) they are not a universal law

(c) the principle of superposition does not apply to both

(d) both are long-range fields

 

Question 4:

The sun gives light at the rate of 1500 W/m² of area perpendicular to the direction of light. Assume the wavelength of light as 5000Å. Calculate the number of photons/s arriving at 1 m² area at that part of the earth.
(a) 4.770 × 10²¹
(b) 3.770 × 10¹¹
(c) 3.770 × 10²¹
(d) 3.770 × 10²⁰

 

Question 5:

A man stands in front of a mirror of special shape. He finds that his image has a very small head, a fat body, and legs of normal size. What can we say about the shapes of the three parts of the mirror?
a) convex, Concave, Plane
b) the plane, Concave, Convex
c) concave, Convex, Plane
d) convex, Plane, Concave

 

Question 6:

Which among the following is true?
(a) according to Kirchhoff’s law, the current flowing towards a junction is equal to the voltage drop
(b) according to Kirchhoff’s law, the current flowing towards a junction is equal to the resistance across the junction
(c) according to Kirchhoff’s law, the current flowing towards a junction is equal to the current leaving the junction
(d) according to Kirchhoff’s law, the current flowing towards a junction is equal to all the currents in the circuit

 

 

Question 7:

What is the maximum torque on a rectangular coil of area 4 cm × 80 cm of 400 turns, when carrying a current of 10³ A in a magnetic field of 0.2 T?

(a) 1250 Nm

(b) 2560 Nm

(c) 3600 Nm

(d) 1985 Nm

 

Question 8:

How does the capacitance change with the effect of the dielectric when the battery remains connected across the capacitor?

(a) increases

(b) decreases

(c) zero

(d) remains constant

 

Question 9:

Four charges are kept at the corner points of a square. The net force on a charge kept at the centre of the square is _________

a) along diagonal

b) zero

c) along one side

d) depends on the nature of the charges

 

 

Question 10:

Which of the following has a low value in ferrites?

(a) conductivity

(b) permeability

(c) magnetic susceptibility

(d) all the above

 

Question 11:

A solenoid is connected to a battery so that a steady current flows through it. If an iron core is inserted into the solenoid, will the current increase or decrease? Explain.

 

Question 12:

 A device ‘X’ is connected to an a.c source. The variation of voltage, current and power in one complete cycle is shown in Fig 7.5.

(a) Which curve shows power consumption over a full cycle?

(b) What is the average power consumption over a cycle?

(c) Identify the device ‘X’

Question 13:

A long straight current carrying wire passes normally through the center of circular loop. If the current through the wire increases, will there be an induced emf in the loop?

 

Question 14:

In a potentiometer arrangement for deter-mining the emf of a cell, the balance point of the cell in open circuit is 350 cm. When a resistance of 9 Q is used in the external circuit of the cell, the balance point shifts to 300 cm. Determine the internal resistance of the cell.

 

Question 15:

What fraction of tritium will remain after 25 years? Given half-life of tritium as 12.5 years.

 

Question 16:

A slit S is illuminated by a monochromatic source of light to give two coherent sources P₁ and P₂. These given bright and dark bands on a screen. At a point R, on the screen, there is a dark fringe. What relation must exist between the lengths P₁R and P₂R?

 

Question 17:

An object is placed between the pole and the focus of a concave mirror produces a virtual and enlarged image. Justify using mirror formula.

 

 

Question 18:

Use Lenz’s law to determine the direction of induced current in the situations described by Figure:

A wire of irregular shape turning into a circular shape;

 

Question 19:

No Two Electric Lines of Force Can Intersect Each Other. Why?

 

Question 20:

Write the truth table for the following combination of gates.

SECTION - B

Question 21:

The variation of the stopping potential (V_o) with the frequency (v) of the light incident on two different photosensitive surfaces M₁ and M₂ is shown in the figure. Identify the surface which has greater value of the work function.

 

Question 22:

Define angle of dip. Deduce the relation connecting angle of dip and horizontal component of earth’s total magnetic field with the horizontal direction.

Question 23:

Answer the following questions, which help you understand the difference between Thomson's model and Rutherford's model better.

(a) Is the average angle of deflection of α-particles by a thin gold foil predicted by Thomson's model much less, about the same, or much greater than that predicted by Rutherford's model?

(b) Keeping other factors fixed, it is found experimentally that for small thickness t, the number of α-particles scattered at moderate angles is proportional to t. What clue does this linear dependence on t provide?

 

Question 24:

Zener diode has saturation current of 20A and reverse breakdown voltage of 100V whereas the corresponding value of are 40μA and 40V. Find the current through the circuit.

    

 

Question 25:

A pair of adjacent coils has a mutual inductance of 2 H. If the current in one coil changes from 0 to 20 A in 1 s. What is the change in flux linkage with the other coil?

 

Question 26:

(i)State the law that gives the polarity of the induced emf.

(ii)A 15 μF capacitor is connected to 220V,50Hz source. Find the capacitive reactance and the rms current.

 

Question 27:

The space between the plates of a parallel plate capacitor is completely filled in two ways. In the first case, it is filled with a slab of dielectric constant K. In the second case, it is filled with two slabs of equal thickness and dielectric constants K₁ and K₂ respectively as shown in the figure. The capacitance of the capacitor is same in the two cases. Obtain the relationship between K, K₁ and K₂.

 

Question 28:

The figure below shows tracks of three charged particles in a uniform electrostatic field. Give the signs of the three charges. Which particle has the highest charge to mass ratio?

 

Question 29:

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 up to the same height, by what distance would the microscope have to be moved to focus on the needle again?

 

Question 30:

A 12.5 eV electron beam is used to bombard gaseous hydrogen at room temperature. What series of wavelengths will be emitted?

 

Question 31:

Answer the following questions:

(a) Why does a paramagnetic sample display greater magnetisation (for the same magnetising field) when cooled?

(b) Why is diamagnetism, in contrast, almost independent of temperature?

(c) If a toroid uses bismuth for its core, will the field in the core be (slightly) greater or (slightly) less than when the core is empty?

 

(d) Is the permeability of a ferromagnetic material independent of the magnetic field? If not, is it more for lower or higher fields?

(e) Magnetic field lines are always nearly normal to the surface of a ferromagnet at every point. (This fact is analogous to the static electric field lines being normal to the surface of a conductor at

every point.) Why?

 

Question 32:

In the Wheatstone bridge given below, what should be values of R₁ and R₂ so that the bridge is balanced?

 

Question 33:

What is the de Broglie wavelength of a nitrogen molecule in air at 300 K? Assume that the molecule is moving with the root-mean-square speed of molecules at this temperature. (Atomic mass of nitrogen = 14.0076 u)

 

Question 34:

Prove that energy stored per unit volume in a capacitor is given by ∈₀E², where E is the electric field of the capacitor.

Section - D

Question 35:

With the help of a labelled circuit diagram, explain full wave rectification using junction diode. Draw input and output wave forms.

 

OR

Distinguish between conductors, insulators and semiconductors on the basis of energy band diagrams.

 

Question 36:

Draw a labelled diagram of telescope when the image is formed at the least distance of distinct vision? Hence derive the expression for its magnifying power.

OR

Drive the expression for the angle of deviation for a ray of light passing through an equilateral prism of refracting angle A.

 

Question 37:

Two wires loops PQRSP formed by joining two semi-circular wires of different radii carry a current I as shown in the figure. What is the direction of the magnetic induction at the centre C.?

OR

(a) Write two main observations of photoelectric effect experiment which could only be explained by Einstein’s photoelectric equation.

(b) Draw a graph showing variation of photocurrent with the anode potential of a photocell.

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