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Questions >> JEEMAIN and NEET >> Physics

Physics

A force F acts between two charges kept 1 cm apart in air. If permittivity of air and dielectric constant of water are $\in _0$ and $K$ respectively, find the force acting when both atoms are placed in water.

asked Jan 3, 2014 by meena.p

1 answer

Total electric flux coming out of unit positive charge put in air is :

asked Jan 3, 2014 by meena.p

1 answer

n identical condensers are joined in series and are charged to potential v. Now they are seperated and joined in parallel. Total energy and potential difference of combination will be :

asked Jan 3, 2014 by meena.p

1 answer

Potential energy of a particle varies as a function of $x$ and is given as $ U(x)$ \[ \begin {bmatrix} E_{\circ} & 0 \leq x \leq 1 \\ 0 & x > 1 \end {bmatrix} \] The de-Broglie wavelengths of the particle in the region $ 0 \leq x \leq1$ and $x>1$ are $ \lambda_1$ and $ \lambda_2$ respectively. If the total energy of the particle is $2E_{\circ}$, the ratio $ \large\frac{\lambda_1}{\lambda_2}$is

asked Jan 1, 2014 by thanvigandhi_1

1 answer

Assume that the de-Broglie wave associated with an electron can form a standing wave between the atoms arranged in a one dimensional array with nodes on each of the atomic site. It is found that one such standing wave is formed if the distance between the atoms of the array is $2\: A^{\circ}$ A similar standing wave is again formed if $d$ is increased to $2.5\: A^{\circ}$ . but not for any other intermediate value of $d$. The energy of the electron is

asked Jan 1, 2014 by thanvigandhi_1

1 answer

Light of wavelength $4000\: A^{\circ}$ and intensity $100 W/m^2$ is incident on a plate of threshold frequency $ 5.5 \times 10^{14}Hz$. The no. of photons incident per $m^2$ per second is

asked Jan 1, 2014 by thanvigandhi_1

1 answer

One milliwatt of light of wavelength of 4560 $A^{\circ}$ is incident on a cesium surface. Calculate the electron current liberated. Assume a quantum efficiency of 0.5%.

asked Jan 1, 2014 by thanvigandhi_1

1 answer

If the speed of photoelectrons is $10^4\: m/s$, what should be the frequency of the incident radiation on a potassium metal? (work function of potassium = $2.3 eV)$

asked Dec 31, 2013 by thanvigandhi_1

1 answer

A photosensitive metallic surface has work function, $hv_{\circ}$. If photons of energy $2hv_{\circ}$ fall on this surface, the electrons come out with a maximum velocity of $4 \times 10^6 \: m/s$. When the photon energy is increased to $5hv_{\circ}$, then maximum velocity of photoelectrons will be

asked Dec 31, 2013 by thanvigandhi_1

1 answer

Threshold wavelength for photoelectric emission from a metal surface is 5200 $A^{\circ}$ will be emitted when this surface is illuminated with monochromatic radiation from . Photoelectrons

asked Dec 31, 2013 by thanvigandhi_1

1 answer

Figure shows the variation of photocurrent with anode potential for a photo-sensitive surface for three different radiations

asked Dec 31, 2013 by thanvigandhi_1

1 answer

A photon of energy 4 eV is incident on a metal surface whose work function is 2 eV. The minimum reverse potential to be applied for stopping the emission of electrons is

asked Dec 31, 2013 by thanvigandhi_1

1 answer

In a series of photoelectric emission experiments, a number of different metals were illuminated with monochromatic light of a number of different photon energies and of different intensities. The variables in the experiment were thus:

asked Dec 31, 2013 by thanvigandhi_1

1 answer

In which of the following cases the heavier of the two particles has a smaller de-Broglie wavelength? The two particles

asked Dec 31, 2013 by thanvigandhi_1

1 answer

Figure shows the results of an experiment involving photoelectric effect. The graphs A,B,C,D relate to light beams having different wavelengths.

asked Dec 31, 2013 by thanvigandhi_1

1 answer

When a monochromatic point source of light is at a distance 0.2 m from a photoelectric cell, the cut- off voltage and the saturation current are respectively 0.6 V and 18 mA. If the same source is placed 0.6 m away from the photocell, then choose the correct option:

asked Dec 31, 2013 by thanvigandhi_1

1 answer

Which of the following statements is not in support of the quantum nature of light?

asked Dec 31, 2013 by thanvigandhi_1

1 answer

The energy that should be added to an electron to reduce its de-Broglie wavelength from 1nm to 0.5 nm is

asked Dec 31, 2013 by thanvigandhi_1

1 answer

The energy of a photon is equal to the KE of a proton. The energy of the photon is E. Let $ \lambda_1$ be the de- Broglie wavelength of the proton and $ \lambda_2$ be the wavelength of the photon. So, $\large\frac{\lambda_1}{\lambda_2}$ is

asked Dec 31, 2013 by thanvigandhi_1

1 answer

We wish to see inside an atom. Assuming the atom to have a diameter of 100 pm, this means that one must be able to resolve a width of say 10 pm. If an electron microscope is used, the minimum electron energy required is about

asked Dec 31, 2013 by thanvigandhi_1

1 answer

Which of the following graphs correctly represents the variation of particle momentum with associated de-Broglie wavelength?

asked Dec 31, 2013 by thanvigandhi_1

1 answer

S1: If momentum of a body increases by 50%, its KE will increase by 125%. S2: KE is proportional to square of velocity.

asked Dec 30, 2013 by thanvigandhi_1

1 answer

S1: If the accelerating potential of an electron is doubled then its velocity becomes 1.4 times. S2: It will move on a circular path with same velocity.

asked Dec 30, 2013 by thanvigandhi_1

1 answer

S1 : When ultraviolet light is incident on a photocell, its stopping potential is $V_{\circ}$ and the maximum kinetic energy of the photoelectrons is $K_{max}$ increase. . When the ultraviolet light is replaced by x-rays, both $V_{\circ}$ and $ K_{max}$ S2 : Photoelectrons are emitted with speeds ranging from zero to a maximum value because of the range of frequencies present in the incident light.

asked Dec 30, 2013 by thanvigandhi_1

1 answer

A radiation of energy $E$ falls normally on a perfectly reflecting surface. The momentum transferred to the surface

asked Dec 30, 2013 by thanvigandhi_1

1 answer

When radiation falls on plate C, the ammeter reading remains zero till jockey is moved from the end P to the middle point of the wire PQ. Therefore the deflection is recorded in the ammeter. The maximum kinetic energy of the emitted electron is :

asked Dec 30, 2013 by thanvigandhi_1

1 answer

Which of the given colors do not show photoelectric effect from this experiment?

asked Dec 30, 2013 by thanvigandhi_1

1 answer

If no radiation is falling on plate C, the number of electrons appeared on the surface of cathode C when jockey is connected at end P of the rheostat is

asked Dec 30, 2013 by thanvigandhi_1

1 answer

De Broglie used Einstein’s special theory of relatively together with Plank’s quantum theory to establish the wave property of particles. He gave fundamental relationship $ \large\frac{ \lambda h}{p}$; where $ lambda$ and $p$ are wavelength and momentum respectively and $h$ is Plank’s constant. A de-Broglie wave associated with an electron can form a standing wave between the atoms arranged in a one dimensional array with node at each of the atomic sites. A standing wave is formed when the distance between the atoms of any array is $d = 3A^{\circ}$. A similar standing wave is again formed if $d = 3.5 A^:{\circ}$ but not for any intermediate value of $d$. For thermal neutron at ordinary temperature, energy is given by relation $E = kT$, where $K$ is Boltzmann constant mass of Neutron is $1.67\times10^{–23} g$. The least value of d for which standing wave can be formed is

asked Dec 30, 2013 by thanvigandhi_1

1 answer

The anode voltage of a photocell is kept fixed. The wavelength $ \lambda$ of the light falling on the cathode is gradually changed. The plate current vs. $ \lambda$ curve is

asked Dec 30, 2013 by thanvigandhi_1

1 answer

The quark structure of protons and neutrons appears at the minute length-scale of $10^{-15}m$ or less. This structure was first probed in early 1970’s using high energy electron beams produced by a linear accelerator at Stanford, USA. Guess the order of energy of these electron beams. (Take wavelength of a proton = $10^{-15}m$ ; rest mass of energy of electron = $0.511\: MeV$)

asked Dec 30, 2013 by thanvigandhi_1

1 answer

Light of Intensity $10^{-5}W/m^2$ falls on a sodium photo-cell of surface area $2\: cm^2$ .Assuming that the top 5 layers of sodium absorb the incident energy, estimate time required for photoelectric emission in the wave – picture of radiation.( Effective atomic area of a sodium atom = $10^{-20}m^2$ )

asked Dec 30, 2013 by thanvigandhi_1

1 answer

A monoenergetic electron beam with speed of $ 5.2 \times 10^6\: m/s$ is subjected to a magnetic field of $1.3 \times 10^{-4}T$ normal to the beam velocity. What is the radius of the circle traced by the beam, given $ \large\frac{e}{m}$ for electron equals $1.76 \times 10^{11}C /kg$?

asked Dec 30, 2013 by thanvigandhi_1

1 answer

In a photocell experiment, a convex lens is used to focus the light beam. Current strength is I. If the lens is replaced by another lens of half diameter, but same focal length, photoelectric current will be

asked Dec 28, 2013 by thanvigandhi_1

1 answer

Maximum velocity of the photoelectrons emitted by a metal surface is $1.2 \times 10^6 m/s$. Assuming the specific charge of the electron to be $1.8 \times 10^{11}C/kg$, the value of the stopping potential is

asked Dec 28, 2013 by thanvigandhi_1

1 answer

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

asked Dec 28, 2013 by thanvigandhi_1

1 answer

When photons of energy hv fall on an aluminum plate (of work function $E_{\circ}$) photoelectrons of maximum $KE,\: K$ are ejected. If the frequency of the radiation is doubled, the maximum kinetic energy of the ejected photoelectrons will be

asked Dec 28, 2013 by thanvigandhi_1

1 answer

A photocell employs photoelectric effect to convert

asked Dec 28, 2013 by thanvigandhi_1

1 answer

In photoelectric effect, the number of electrons ejected per second is

asked Dec 28, 2013 by thanvigandhi_1

1 answer

Relation of the stopping potential $V_{\circ}$ of a metal and the maximum velocity $v$ of the photoelectrons

asked Dec 28, 2013 by thanvigandhi_1

1 answer

Graph of $KE_{max}$ of the photoelectrons against v the frequency of the radiation incident on the metal is a straight line of slope equal to: , i

asked Dec 28, 2013 by thanvigandhi_1

1 answer

If in a photoelectric experiment, the wavelength of incident radiation is reduced from $6000\: A^{\circ} \: to \: 4000\: A^{\circ}$ , then

asked Dec 28, 2013 by thanvigandhi_1

1 answer

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

asked Dec 28, 2013 by thanvigandhi_1

1 answer

An electron is accelerated through a potential difference of V volt. It has a wavelength $ \lambda$ associated with it. Through what potential difference must an electron be accelerated so that its de-Broglie wavelength is the same as that of a proton? Take mass of a proton to be 1837 times larger than the mass of electron.

asked Dec 27, 2013 by thanvigandhi_1

1 answer

When the momentum of a proton is changed by an amount $p_{\circ}$, the corresponding change in de- Broglie wavelength is found to be $0.25 \%$. Then, the original momentum of the proton was

asked Dec 27, 2013 by thanvigandhi_1

1 answer

What is the effect of increasing the intensity of light that falls on the emitter in a photoelectric effect apparatus?

asked Dec 27, 2013 by thanvigandhi_1

1 answer

Mark the correct one

asked Dec 27, 2013 by thanvigandhi_1

1 answer

Which statement is incorrect regarding photoelectric effect?

asked Dec 27, 2013 by thanvigandhi_1

1 answer

The graph between stopping potential vs frequency is given for two different metals, then choose most appropriate statement

asked Dec 27, 2013 by thanvigandhi_1

1 answer

Two identical photo cathodes receive light of frequencies $f_1\: and \: f_2$. If velocities of photoelectrons (of mass m) coming out are respectively $v_1\: and\: v_2$, then

asked Dec 27, 2013 by thanvigandhi_1

1 answer

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