RBSE Class 12th Physics 2022

RBSE Class 12^th Physics 2022

1.(i) The SI unit of electric flux is

(a) NC^-1 m²

(b) NC^-1 m^-2

(d) N^-1C¹ m²

Ans (a) NC^-1 m²

(ii) The dependence of electric potential (V) on distance (r) inside a uniformly charged spherical shell is-

(a) V∝ r

(b) V= constant

(d) V∝ 1/r²

Ans (b) V= constant

(iii) In meterbridge experiment, the blance points is founded to be at 20 cn dustabce frin end A when R = 3Ω resistor applied between A and B, The the value of unknown resistance S will be-

(a) 3Ω

(b) 6Ω

(d) 10Ω

Ans (c) 12Ω

(iv) The correct relationship between the permittivity of free space (ε₀), the permeability of free space (µ₀) and the velocity of light in vacuum (c) is-

(a) $\displaystyle {{\mu }_{0}}{{\in }_{0}}={{c}^{2}}$

(b) $\displaystyle \frac{1}{{{{\mu }_{0}}{{\in }_{0}}}}={{c}^{2}}$

(d) $\displaystyle \frac{1}{{\sqrt{{{{\mu }_{0}}{{\in }_{0}}}}}}={{c}^{2}}$

(v). A moving charge can produce-

(a) Only electric field

(b) Only magnetic field

(d) None of these

Ans (c) Both electric & magnetic field

(vi) Eddy currents are used in –

(a) Magnetic braking in trains

(b) Induction furnace

(d) Allof the above

Ans (d) Allof the above

(vii) If refractive index of denser medium 1 with respect to rarer medium 2 is n₁₂ and critical angle for this pair of media is i_c, then correct relation between n₁₂ and i_c is-

(a) $\displaystyle {{n}_{{12}}}=\sin {{i}_{c}}$

(b) $\displaystyle {{n}_{{12}}}=\tan {{i}_{c}}$

(d) $\displaystyle {{n}_{{12}}}=\frac{1}{{\sin {{i}_{c}}}}$

Ans (d) $\displaystyle {{n}_{{12}}}=\frac{1}{{\sin {{i}_{c}}}}$

(viii) In an experimental study of photoelectric effect, the correct graph between collector plate potential and photoelectric current for different intensities of incident radiation is-

(a)

(b)

(c)

(d)

Ans (a)

(ix) Who first experimentally verified the wave nature of the electron?

(a) Whihelm Hallwachs and Philipp Lenard

(b) C.J. Davission and L.H. Germer

(d) A.H.Compton

Ans (b) C.J. Davission and L.H. Germer

2. Fill in the blanks (i) to (iv)

(i) The name of machine that accelerates charged particles or ions to high energies is —-

Ans Cyclotron.

(ii) The ratio of flux linkage (N𝜙) associated with a coil having N turns to the current (I) flowing through it $\displaystyle \left( {\frac{{N\phi }}{I}} \right)$ is ———-

Ans Self inductance

(iii) If —— of two particles are equal, then their de Broglie wavelength will be equal.

Ans Momentum (p)

(iv) The ———— are majority charge carries and ——– are minority charge carriers in p-type semiconductor.
Ans (i) holes (ii) electrons

3. Give the answer (i to viii)

(i) In Milikan’s experiment, the charge found on a charged droplet was $\displaystyle -6.4\times {{10}^{{-19}}}$ C, then write the number of electrons in that charged droplet.

Ans Charged on the droplet = $\displaystyle -6.4\times {{10}^{{-19}}}$ C

We know that charge on a body is integral multiple of quanta of charge, if there are n electrons,

i.e. Q = ne

thus $\displaystyle -6.4\times {{10}^{{-19}}}$ = ne

$\displaystyle -6.4\times {{10}^{{-19}}}$ = $\displaystyle n\times \left( {-1.6\times {{{10}}^{{-19}}}} \right)$

n = 4

thus, there are 4 electrons in the drop.

(ii) Write the value of electric potential at qa distance r from the middle point of the dipole on the axis of the electric dipole of dipole moment p.

Ans Dipole moment = p

Distance = r

Since point is on the axis

Therefore Q = $\displaystyle {{0}^{\circ }}$

By formula of potential due to electric dipole,

$\displaystyle v=\frac{{kp\cos \theta }}{{{{r}^{2}}}}$

$\displaystyle v=\frac{{9\times {{{10}}^{9}}\times p\times \cos \theta }}{{{{r}^{2}}}}\equiv 1$

$\displaystyle v=\frac{{9p}}{{{{r}^{2}}}}\times {{10}^{9}}$

Or $\displaystyle v=\frac{{kp}}{{{{r}^{2}}}}$ volt

$\displaystyle k=\frac{1}{{4r{{\in }_{0}}}}$ for vacuum

(iii) Write dependence of resistivity with temperature for semiconductors.

Ans We know that resistivity of semiconductors decrease with increase in temperatures. It is show below.

For semiconductor temperature coefficient of resistivity is negative

i.e. ∝ → -ive

by formula $\displaystyle \frac{{p-{{p}_{0}}}}{{{{p}_{0}}}}=\propto \Delta T$

$\displaystyle p={{p}_{0}}(1+\propto \Delta T)$

Since ∝ < 0

or ∝∆T<0

or 1+∝∆T<0

thus $\displaystyle \frac{p}{{{{p}_{0}}}}$ < 1

or $\displaystyle p<{{p}_{0}}$

So final resistivity is less than initial resistivity.

Thus, for semiconductors

$\displaystyle T\uparrow$ then $\displaystyle p\downarrow$

$\displaystyle T\downarrow$ then $\displaystyle p\uparrow$

So $\displaystyle T\propto \frac{1}{p}$

(iv) If two cell of e.m.f. $\displaystyle {{\varepsilon }_{1}},{{\varepsilon }_{2}}$ and internal resistance r₁.r₂ are connected in parallel combination, then write the equivalent e.m.f. of this combination.

Ans We have $\displaystyle \left( {{{\varepsilon }_{1}},{{r}_{1}}} \right)$ and $\displaystyle \left( {{{\varepsilon }_{2}},{{r}_{2}}} \right)$ in parallel,

Thus their equivalent resistance

$\displaystyle \frac{1}{{{{r}_{{eq}}}}}=\frac{1}{{{{r}_{1}}}}+\frac{1}{{{{r}_{2}}}}$

$\displaystyle {{r}_{{eq}}}=\frac{{{{r}_{1}}{{r}_{2}}}}{{{{r}_{1}}+{{r}_{2}}}}$

Also, equivalent e.m.f.

$\displaystyle \frac{{{{\varepsilon }_{{eq}}}}}{{{{r}_{{eq}}}}}=\frac{{{{\varepsilon }_{1}}}}{{{{r}_{1}}}}+\frac{{{{\varepsilon }_{2}}}}{{{{r}_{2}}}}$

$\displaystyle {{\varepsilon }_{{eq}}}=\frac{{{{\varepsilon }_{1}}{{r}_{2}}+{{\varepsilon }_{2}}{{r}_{1}}}}{{{{r}_{1}}{{r}_{2}}}}\times {{r}_{{eq}}}$

$\displaystyle {{\varepsilon }_{{eq}}}=\frac{{{{\varepsilon }_{1}}{{r}_{2}}+{{\varepsilon }_{2}}{{r}_{1}}}}{{{{r}_{1}}{{r}_{2}}}}\times \left( {\frac{{{{r}_{1}}{{r}_{2}}}}{{{{r}_{1}}+{{r}_{2}}}}} \right)$

$\displaystyle {{\varepsilon }_{{eq}}}=\frac{{{{\varepsilon }_{1}}{{r}_{2}}+{{\varepsilon }_{2}}{{r}_{1}}}}{{{{r}_{1}}+{{r}_{2}}}}$ volt

(v) How can a galvanometer be converted into a voltmeter?

Ans. We can convert a Galvanometer into a voltmeter by adding a high resistance (RH) in series of the galvanometer,

Since net resistance RG + RH ≡ RH

Then V = IR ≡ constant

The correct voltage is measured.

(vi) Draw a diagram of the magnetic field lines due to a current carrying circular loop.

Ans.

(vii) Write Faraday’s law of electromagnetic induction.

Ans. According to faraday’s law of electromagnetic induction, “The emf induced in the coil is equal to the rate of change of magnetic flux through it”

Mathematically

$\displaystyle \varepsilon =-N\frac{{d{{\phi }_{B}}}}{{dt}}$ volt

(viii) Draw a graph between angle of incidence (i) and angle of deviation (δ) for triangular prism.

Ans

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Section B

4. If the area of each conduction plate of parallel plate capacitor is A & d is the separation between them, then derive its capacitance formula.

Ans

5. If C1, C2, C3, C4, C5 five capacitors are connected in an electrical circuit as shown in figure, then calculate the equivalent capacitance of this mesh(network) between point A & point B.

Ans

6. Carbon resistors are widely used in electronic circuits. Why? Write any two reasons.

7. If 12 resistors each of resistance 12 Ω are connected in a cubical network, then determine the equivalent resistance of this network across the diagonally opposite corners of the cube.

8. If the focal length of a concave mirror is f and radius of curvature is R, then prove that radius of curvature is twice the focal length.

9. If a concave lens of 25 cm focal length is placed in contact with a convex lengs of 20 cm focal length, then calculate the power of the combined lens formed by this combination.

10. By writing Einstein’s photoelectric equation, explain any two observations related to photoelectric effect.

11. Calculate the de Broglie wavelength associated with an electron, accelerated through a potential difference of 100 V.

12. What is meant by half-life of radioactive nuclei? Write the relation between half-life and mean life of a radioactive nuclie.

13. Write any three features of the nuclear force.

14. Write the working of a voltage regulator made by using a Zener diode.

Ans

15. A circuit is shown in the figure by combining two NOT gates and one NOR gate. Write the truth table for this connected circuit.

Ans

Section – C

16. Write Gauss’s law. Using this law, find the electric field due to a uniformly charged infinite plane sheet at a point near the sheet.

Write the definition of electric dipole. An electric dipole is placed in a uniform external electric field $\displaystyle \left( {\overrightarrow{E}} \right)$ as shown in the figure. Calculate the torque on this electric dipole.

Ans

17. If a metal rod of length l is placed normal to a uniform magnetic field (B) and moved with a velocity (v) perpendicular to the magnetic field, then find the induced emf (motional emf) between its ends. Draw the necessary diagram.

In an ac generator, a rectangular coil of N turns and cross-section A is rotated in uniform magnetic field (B) with a uniform angular speed w, then find the instantaneous value of the induced emf in it. Draw the necessary diagram.

18. What is meant by mass defect and nuclear binding energy? Draw a graph between mass number and binding energy per nucleon.

Explain the following in a nuclear rector based on thermal neutron fission.

(i) The modertor

(ii) The coolant

Draw a block diagram of the reactor.

SECTION-D

19. What is meant by compound microscope? Draw a ray diagram of the formation of an image by a compound microscope. Briefly describe its working and derive the formula for its total magnification.

What is meant by Telescope? Draw a ray diagram of image formation by a refraction telescope. Briefly describe its working and derive the formula for its magnifying power.

20. What is meant by forward bias and reverse bias of p-n junction diode? Draw an experimental electric circuit diagram to study the V-I characteristics in the forward bias and reverse bisa of a p-n junction diode. Draw forward & reverse bias V-I characteristics curves for p-n junction diode and explain the following in brief.

(i) Thershold or cut in voltage

(ii) Breakdown voltage.

What is meant by ratification? Draw an electric circuit diagram of a half wabe rectifier. Write a brief description of its working. Draw input and output voltage waveforms for this rectifier circuit.

RBSE Class 12th Physics 2022

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RBSE Class 12^th Physics 2022