Recent questions in Physics

According to Einstein’s photoelectric equation, the plot of the KE of the emitted photoelectrons from a metal vs the frequency of the incident radiation gives a straight line whose slope

asked Dec 27, 2013 by thanvigandhi_1

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If the KE of a free electron doubles, its de Broglie wavelength changes by a factor:

asked Dec 27, 2013 by thanvigandhi_1

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An electron is 2000 times lighter than a proton. Both are moving such that their matter waves have a length of $ 1\: \dot {A}$. The ratio of their kinetic energy in approximation is

asked Dec 27, 2013 by thanvigandhi_1

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The work function of a substance is $4.0\: eV$. The longest wavelength of light that can cause photoelectron emission from this substance is approximately

asked Dec 27, 2013 by thanvigandhi_1

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A proton, a deuteron and an alpha particle are accelerated through potentials of $V,\: 2V\: and\: 4V$ respectively. Their velocities will bear a ratio

asked Dec 27, 2013 by thanvigandhi_1

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A photoelectric cell is illuminated by a small bright source of light placed at 1m. If the same source of light is placed 2m away, the electrons emitted by the cathode

asked Dec 27, 2013 by thanvigandhi_1

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Light of wavelength $0.6\: \mu m$ from a sodium lamp falls on a photocell and causes the emission of photoelectrons for which the stopping potential is $0.5\: V$ and with light of wavelength $0.4\: \mu m$ from a sodium lamp, the stopping potential is $1.5\: V$. With this data, the value of $ \large\frac{h}{e}$ will be

asked Dec 27, 2013 by thanvigandhi_1

1 answer

When a light of wavelength $300\: nm$ falls on a photoelectric emitter, the photoelectrons are liberated. For another emitter, the light of wavelength $600\: nm$ is sufficient for liberating photoelectrons. The ratio of the work function of the two emitters, is

asked Dec 27, 2013 by thanvigandhi_1

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From this figure describing photoelectric effect, we may infer correctly that :

asked Dec 27, 2013 by thanvigandhi_1

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De Broglie wavelength of photoelectrons is $1\: A^{\circ}$ . What is stopping potential?

asked Dec 27, 2013 by thanvigandhi_1

1 answer

In an accelerator experiment on high – energy collisions of electrons with positrons, a certain event is interpreted as annihilation of an electron – positron pair of total energy $10.2\: BeV$ into two $ \gamma$-rays of equal energy. What is the wavelength associated with each $ \gamma$-ray? $(1\; Bev = 10^9\: eV)$

asked Dec 27, 2013 by thanvigandhi_1

1 answer

Find the de Broglie $ \lambda$ of a neutron, in thermal equilibrium with matter, having an average $KE\: of \bigg(\large\frac{3}{2} \bigg)\: kT$ at $300 \: K.$

asked Dec 27, 2013 by thanvigandhi_1

1 answer

The typical de Broglie wavelength associated with a $He$ atom in $He$ gas at room temperature $(27^{\circ}C)$ and $1 \: atm$ pressure is $ \lambda$, and the mean separation between two atoms under these conditions is $r.$

asked Dec 27, 2013 by thanvigandhi_1

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Crystal diffraction experiments can be performed using X – rays, or electrons accelerated through appropriate voltage. Which probe has greater energy? (Take wavelength of probe = $1 A^{\circ}$ )

asked Dec 27, 2013 by thanvigandhi_1

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Monochromatic radiation of wavelength $640.2\: nm$ from a neon lamp irradiates photosensitive material made of cesium on tungsten. The stopping voltage is measured to be $0.54\: V$. The source is replaced by an iron source and its $427.2\: nm$ light irradiates then same photocell. Predict the new stopping voltage.

asked Dec 25, 2013 by thanvigandhi_1

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Ultraviolet light of wavelength $2271\: A^{\circ}$ from a $100\: W$ mercury source irradiates a photocell made of molybdenum metal. If the stopping potential is $-1.3\: V$,will the photocell respond to a high intensity $(10^{-5}W/m^2)$ red light of wavelength $632.8\: A^{\circ}$ produced by a He-Ne laser?

asked Dec 25, 2013 by thanvigandhi_1

1 answer

Find the number of photons entering the pupil of our eye per second corresponding to the minimum intensity of white light that humans can perceive $(10^{-10}W/m^2$ ).( Assume area of pupil to be $0.4 cm^2$ , and average frequency of white light to be $6 \times 10^{14}Hz)$

asked Dec 25, 2013 by thanvigandhi_1

1 answer

An electron gun with its collector at a potential of $100 \;V$ fires out electrons in a spherical bulb containing hydrogen gas at low pressure $(10^{-2}\: mm \: of\: Hg)$ A magnetic field of $2.83 \times 10^{-4} \: T$ curves the path of the electrons in a circular orbit of radius $12\; cm$. Find e/m of the electron.

asked Dec 25, 2013 by thanvigandhi_1

1 answer

What is the de Broglie wavelength of a nitrogen molecule in air at $300\; K?$ Assume molecule is moving with the rms speed of molecules at this temp. At. mass of $N= 14.0076 \; u$

asked Dec 25, 2013 by thanvigandhi_1

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The $ \lambda$ of light from the spectral emission line of sodium is $589\: nm$. Find the $KE$ at which an electron would have the same de Broglie wavelength.

asked Dec 25, 2013 by thanvigandhi_1

1 answer

The momentum of the electrons accelerated through a potential difference of $56\; V$ is

asked Dec 25, 2013 by thanvigandhi_1

1 answer

Light of wavelength $488\: nm$ is produced by an argon laser which is used in the photoelectric effect. When light from this spectral line is incident on the emitter, the cut-off potential of photoelectrons is $0.38\: V$. The work function of the material from which the emitter is made is

asked Dec 24, 2013 by thanvigandhi_1

1 answer

In an experiment on photoelectric effect, the slope of the cut-off voltage versus frequency of incident light is found to be $4.12 \times 10^{-15}Vs$. Calculate the value of Planck’s constant.

asked Dec 24, 2013 by thanvigandhi_1

1 answer

Which of the following is correct?

asked Dec 24, 2013 by thanvigandhi_1

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Emission of photoelectrons from a metal plate illuminated with monochromatic electromagnetic radiation will always take place provided

asked Dec 24, 2013 by thanvigandhi_1

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A point source of light is taken away from the experimental setup of photoelectric effect, then which is the most appropriate statement?

asked Dec 24, 2013 by thanvigandhi_1

1 answer

The $KE$ of an electron with de-Broglie wavelength of $0.3\: nm$ is

asked Dec 24, 2013 by thanvigandhi_1

1 answer

Consider two light sources of wavelengths $ \lambda_1\: and\: \lambda_2 (\lambda_1 > \lambda_2)$ which are emitting $n_1\: and \: n_2$ photons respectively, in a given time. Assume equal power for both sources, then

asked Dec 24, 2013 by thanvigandhi_1

1 answer

Sodium and Copper have work functions $2.3\: eV\: and \: 4.5\: eV$ respectively. Then the ratio of the wavelengths is nearest to

asked Dec 24, 2013 by thanvigandhi_1

1 answer

The work function of a substance is $4\: eV$. The longest wavelength of light that can cause photoelectron emission from this substance is approximately

asked Dec 24, 2013 by thanvigandhi_1

1 answer

A source of light is placed at a distance $x$ from a photocell and cut off potential is $V$. If the distance of the same source from the photocell is doubled, then cut off potential will be :

asked Dec 24, 2013 by thanvigandhi_1

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Blue light can cause photoelectric emission from a metal, but yellow light cannot. If red light is incident on the metal, then

asked Dec 24, 2013 by thanvigandhi_1

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The maximum energy of the electrons released in photocell is independent of

asked Dec 24, 2013 by thanvigandhi_1

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The energy $E$ and the momentum $p$ of photon are given by $E=hn\: and\: p=h/\lambda$ respectively. The velocity of photon will be

asked Dec 24, 2013 by thanvigandhi_1

1 answer