Physics 2023 Paper with Solution

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

Physics 2023 Paper with Solution

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