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Physics Test - 20

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Physics Test - 20
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  • Question 1
    1 / -0

    Which of the following gates serve as building blocks in digital circuits?

    Solution

    NAND Implementation:

    NOR Implementation:

     

    NAND and NOR gates are known as universal gates. Any one of these gates can be used to implement any kind of logic gate. This kind of feasibility does not exist with other gates i.e. any other gate cannot solely implement all logic gates. For example, AND gate cannot be implemented using an OR gate and vice-versa. The implementation of NAND and NOR gates to generate other logic gates is shown above.

     

  • Question 2
    1 / -0
    The period of oscillation of a simple pendulum is \({T}=2 \pi \sqrt{\frac{{L}}{{g}}} \) Measured value of \({L}\) is \(10\) cm known to \(1\) mm accuracy and time for \(100\) oscillations of the pendulum is found to be \(50\) s using a wristwatch of \(1\) s resolution. What is the accuracy in the determination of g?
    Solution
    Here, \({T}=2 \pi \sqrt{\frac{{L}}{{g}}}\)
    Squaring both sides, we get, \({T}^{2}=\frac{4 \pi^{2} {L}}{{g}}\) or \({g}=\frac{4 \pi^{2} {L}}{{T}^{2}}\)
    The relative error in \({g}\) is, \(\frac{\Delta {g}}{{g}}=\frac{\Delta {L}}{{L}}+2 \frac{\Delta {T}}{{T}}\)
    Here, \({T}=\frac{{t}}{{n}}\) and \(\Delta {T}=\frac{\Delta {t}}{{n}} \therefore \frac{\Delta {T}}{{T}}=\frac{\Delta {t}}{{t}}\)
    The errors in both Land t are the least count errors. \(\therefore \frac{\Delta {g}}{{g}}=\frac{0.1}{10}+2\left(\frac{1}{50}\right)=0.01+0.04=0.05\)
    The percentage error in \({g}\) is \(\frac{\Delta {g}}{{g}} \times 100=\frac{\Delta {L}}{{L}} \times 100+2\left(\frac{\Delta {T}}{{T}}\right) \times 100=\left[\frac{\Delta {L}}{{L}}+2\left(\frac{\Delta {T}}{{T}}\right)\right] \times 100=0.05 \times 100=5 \%\)
  • Question 3
    1 / -0

    A scooter of mass \(120\) kg is moving with a uniform velocity of \(108\) km/h. The force required to stop the vehicle in \(10\) sec:

    Solution

    Given,

    Massof a scooter, \(m=120\) kg

    Velocity \(v=108\) km/h \(=108 \times \frac{5}{18} = 30\)m/s

    Time taken to stop \(t=10\) sec

    Final velocity, \(v = 0\) m/s​

    From the first equation of motion,

    \(v=u+a t\)

    \(0=30+a \times 10\)

    \(a=-\frac{30 }{ 10}=-3\)m/s\(^2\)

    Since force cannot be negative we will use a positive value for acceleration.

    Force, \(F = m a\)

    \(= 120 × 3 = 360 \) N

  • Question 4
    1 / -0

    A photon of energy \(h \nu\) is absorbed by a free electron of a metal having work function \(\phi

    Solution

    We know that the photoelectric effect of the electron is the emission of the electron due to electromagnetic radiation. This photo electron gets excited and leaves the metal, commonly called photo emission.

    Then the energy \(E\) of the photoelectron is given by Planck as:

    \(E=h \nu=\frac{h c}{\lambda}\) 

    Where, \(h\) = Planck's constant, \(\nu\) = frequency of the incident light, \(c\) = speed of light  \(\lambda\) = wavelength of the incident light

    Also, the frequency of the incident light and the kinetic energy is related as,

    \(E_{p}=\phi+E_{e}\),

    Where \(E_{p}\) = energy of the photon, \(\phi\) = work function,  \(E_{e}\) = energy of the photoelectron.

    Given that, \(\phi

  • Question 5
    1 / -0

    A planet is revolving around the sun in an elliptical orbit. Which of the following remains constant?

    Solution

    According to Kepler's second law, the angular momentum of the planet is constant. The angular momentum of the planet does not vary, i.e., the aerial velocity of the planet remains constant.

  • Question 6
    1 / -0

    The process in which an electron escapes from the metal surface is called:

    Solution

    The process in which an electron escapes from the metal surface is known as electron emission. This occurs due to various mechanisms such as heating (thermionic emission), exposure to light (photoelectric emission), or application of a strong electric field (field emission). Once freed, these electrons contribute to electrical conductivity or can be manipulated for various technological applications like vacuum tubes or semiconductor devices. 

  • Question 7
    1 / -0

    A wheel is rotating at the rate of \(33\) revolution/min. if it comes to a stop in \(20\) seconds. Then the angular retardation will be

    Solution

    Given that,

    The initial angular velocity of the wheel, \(\left(\omega_{i}\right)=33\) revolution/min

    The Final angular velocity of the wheel, \(\left(\omega_{f}\right)=0\)

    Time taken by wheel to stop \(t=20~s\)

    We know that,

    The initial angular velocity in \({rad}/s, \left(\omega_{i}\right)\) is given by

    \(= 33 \times \frac{2 \pi}{60}\) (\(\frac{2 \pi}{60}\) is the conversion factor from revolution/minute to \(rad/s\))

    \(= 1.1 \pi~ rad / s\)

    The angular retardation can be calculated by using the formula,

    (Since retardation is mentioned, hence we have to take the negative value of alpha and not positive value).

    \(\omega_{f}=\omega_{i}-\alpha t\) (Putting the values given in the question, we have the following)

    \(\Rightarrow 0=1.1 \pi-\alpha \times 20\)

    \(\Rightarrow \alpha=\frac{1.1 \pi}{20}\)

    \(=\frac{11 \pi}{200} \mathrm{~rad} / \mathrm{s}^{2}\)

  • Question 8
    1 / -0

    Five identical charges \({R}\) are placed equidistant on a semicircle as shown in the figure. Another point charge \(q\) is kept at the center of the circle of radius \({R}\). Calculate the electrostatic force experienced by the charge \(q\).

    Solution

    Force acting on \(q\) due to \(\mathrm{Q}_{1}\) and \(\mathrm{Q}_{5}\) are opposite direction, so cancel to each other. Force acting on \(q\) due to 

    \(\mathrm{Q}_{3}\) is \(\mathrm{F}_{3}=\frac{1}{4 \pi \varepsilon_{0}} \frac{q Q_{3}}{R^{2}}\)

    Force acting on \(q\) due to \(Q_{2}\) and \(Q_{4}\)

    Resolving in two component method:

    (i) Vertical Component: \(\mathrm{Q}_{2} \operatorname{Sin} \theta\) and \(\mathrm{Q}_{4} \operatorname{Sin} \theta\) are equal and opposite direction, so they are cancel to each other.

    (ii) Horizontal Component: \(\mathrm{Q}_{2} \operatorname{Sin} \theta\) and \(\mathrm{Q}_{4} \cos \theta\) are equal and same direction, so they can get added.

    \(F_{24}=F_{2 q}+F_{4 q}=F_{2} \cos 45^{\circ}+F_{4} \cos 45^{\circ}\)

    \(F_{24}=\frac{1}{4 \pi \varepsilon_{0}} \frac{q Q_{2}}{R^{2}} \cos 45^{\circ}+\frac{1}{4 \pi \varepsilon_{0}} \frac{q Q_{ 4}}{R^{2}} \cos 45^{\circ}\)

    Resultant net force \(\mathrm{F}\)

    \(\mathrm{F}=\mathrm{F}_{3}+\mathrm{F}_{24}+\mathrm{F}_{15}\)

    \(\cos 45^{\circ}=\frac{1}{\sqrt{2}}\)

    \(\ \mathrm{F} =\frac{q \mathrm{Q}}{4 \pi \varepsilon_{0} \mathrm{R}^{2}}\left[1+\frac{1}{\sqrt{2}}+\frac{1}{\sqrt{2}}\right]\)

    \(=\frac{1}{4 \pi \varepsilon_{0}} \frac{q \mathrm{Q}}{\mathrm{R}^{2}}\left[1+\frac{2}{\sqrt{2}}\right]\)

     \(\mathrm{F} =\frac{1}{4 \pi \varepsilon_{0}} \frac{q \mathrm{Q}}{\mathrm{R}^{2}}[1+\sqrt{2}] \mathrm{N} \)

    Vector form:

    \(\overrightarrow{\mathrm{F}}=\frac{1}{4 \pi \varepsilon_{0}} \frac{q \mathrm{Q}}{\mathrm{R}^{2}}(1+\sqrt{2}) \mathrm{N} \hat{i}\)

  • Question 9
    1 / -0

    The increase in the width of the depletion region in a p-n junction diode is due to

    Solution

    The increase in the width of the depletion region is due to the absence of the electrons and holes in the region. This occurs only in the case of the reverse bias only in a diode.

  • Question 10
    1 / -0

    Which of the following options is correctly depicting the formula of power?

    Solution

    Electric Power: The rate at which electrical energy is dissipated into other forms of energy is called electrical power i.e.,

    \(P=\frac{W}{t}=V I=I^{2} R=\frac{V^{2}}{R}\)

    Where V = Potential difference, R = Resistance and I = current

    From above equation it is clear that all options are correct.

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