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Class 12th Physics Nuclei

If T is the half-life of a radioactive material, then the fraction that would remain after a time $\frac{T}{2} i s$

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Vishal Baghel

Contributor-Level 10

$\begin{array}{l} t = \frac{T}{2} \\ \Rightarrow N = N_{0} {(\frac{1}{2})}^{\frac{t}{T}} \end{array}$

$\Rightarrow N = N_{0} {(\frac{1}{2})}^{\frac{1}{2}} = \frac{N_{0}}{\sqrt[]{2}}$

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Class 12th Physics Ray Optics and Optical Instruments

A telescope with objective of focal length $100 c m$ and eyepiece of focal length $5 c m$ is focused on a far object such that parallel rays emerge from eyepiece. If object subtends an angle of $1^{0}$ on objective, the angular size of image is

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alok kumar singh

Contributor-Level 10

Magnify power of telescope for far point is given as

$m = \frac{θ_{i}}{θ_{0}} = \frac{f_{0}}{f_{e}}$

$? θ_{i} = θ_{0} (\frac{f_{0}}{f_{e}}) {= 1}^{0} (\frac{100}{5}) = 20^{0}$

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Class 12th Physics

Resistance of given carbon resistor is

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Vishal Baghel

Contributor-Level 10

$01 * 1 0^{4} Ω \pm 5 % = 10 * 1 0^{3} Ω \pm 5 %$

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Class 12th Physics Ray Optics and Optical Instruments

Deviation of light ray by a thin prism of refractive index $μ$ and refracting angle $A$ is

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alok kumar singh

Contributor-Level 10

For thin prism, deviation $= (μ - 1) A$

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Class 12th Physics

What is the current through an ideal P – N junction diode shown in figure below?

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Vishal Baghel

Contributor-Level 10

$\Rightarrow l = \frac{2}{50} = 40 m A$

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Class 12th Physics

The value of alternating emf (E) in the given circuit will be

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Vishal Baghel

Contributor-Level 10

$E = \sqrt[]{V_{R}^{2} + {(V_{L} - V_{C})}^{2}}$

$E = \sqrt[]{{(60)}^{2} + {(100 - 20)}^{2}}$

E = 100V

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Class 12th Electromagnetic Induction

Two conducting rods inclined at $' θ'$ angle from horizontal are kept parallel at separation $' l'$ to each other. A resistor of resistance $R$ joins the two rods at their topmost point. A metal bar of length $' l'$ is free to slide on the rods as shown in figure. on releasing from rest, the maximum speed that can be attained by the bar if a constant magnetic field $B$ exists vertically downwards, is

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alok kumar singh

Contributor-Level 10

$F = i l * B$

$? m g \sin ? θ = i l * B$

$? m g \sin ? θ = (\frac{B \cos ? θ l v}{R}) l B \cos ? θ$

$? V = \frac{R m g \sin ? θ}{B^{2} l^{2} \cos^{2} ? θ}$

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Class 12th Physics Ray Optics and Optical Instruments

A farsighted person cannot focus distinctly objects closer than 100cm. The lens that will permit him to read from a distance of 50cm, will have a focal length:

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Vishal Baghel

Contributor-Level 10

$\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$

$\Rightarrow \frac{1}{f} = \frac{1}{- 100} - \frac{1}{- 50} = \frac{1}{50} - \frac{1}{100}$

$\Rightarrow f = + 100 c m$

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Class 12th Physics

Figure shown four plates each of area A and separated from another by a distance d. What is the capacitance between P and Q?

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Vishal Baghel

Contributor-Level 10

$C_{e q} = 2 C = \frac{2 A ε_{0}}{d}$

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Class 12th Physics

A charged particle of mass m and charge q is released from rest in a uniform electric field E. The KE of particle after time t is:

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Vishal Baghel

Contributor-Level 10

$F = q E a = \frac{q E}{m}$

$\Rightarrow s = \frac{1}{2} a t^{2} = \frac{1}{2} (\frac{q E}{m}) t^{2}$

$\Rightarrow W o r k d o n e = Δ K$

$\Rightarrow Δ K = F . s = \frac{q^{2} E^{2} t^{2}}{2 m}$

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