Intensity vs Photocurrent

Q. Two small spheres, each having a mass of 20 g, are suspended from a common point by two insulating strings of length 40 cm each. The spheres are identically charged and the separation between the balls at equilibrium is found to be 4cm. Find the charge on each sphere

Q. 23. Two identical pith balls are charged by rubbing againsteach other. They are suspended from a horizontal rodthrough two strings of length 20 cm each, the separationbetween the suspension points being 5 cm. Inequilibrium, the separation between the balls is 3 cm.Find the mass of each ball and the tension in the strings.The charge on each ball has a magnitude 2.0x 108 C

Q. Two point charges having equal charges separated 1m distance experience a force of 8N. What will be the force experience by them, if they are held in water, at the same distance? Given k water = 80

Q. a charged metallic bob of mass m, ch^° arge Q makes an 60^° with vertical of lenght l is in equilibrium in presemce of electric repulsionby Q(fixd at emean position.what is Q

Q.

There are two charges +1uc and +5uc. what is the ratio of the force acting on them?

Q. An electric bulb is rated as $200\text{W}.$ What will be the peak magnetic field at $4\text{m}$ distance produced by the radiations coming from this bulb? Consider this bulb as a point source with $3.5\%$ efficiency.

1. $1.71\times {10}^{-8}\text{T}$
2. $1.19\times {10}^{-8}\text{T}$
3. $3.36\times {10}^{-8}\text{T}$
4. $0.84\times {10}^{-8}\text{T}$

Q. In a hydrogen atom, the electron makes $6.6\times {10}^{15}\text{revolutions per second}$ around the nucleus in an orbit of radius $0.5\times {10}^{-10}\text{m}$. It is equivalent to a current nearly

1. $1\text{A}$
2. $1\text{mA}$
3. $1\mu \text{A}$
4. $1.6\times {10}^{-19}\text{A}$

Q. Ultraviolet light of wavelength 300 nm and intensity $1.0watt/m^2$ falls on the surface of a photosensitive material. If 1% of the incident photons produce photoelectrons, then the number of photoelectrons emitted from an area of $1.0c{m}^2$ of the surface is nearly

1. $9.61\times {10}^{14}$ per sec
   
2. $4.12\times {10}^{13}$ per sec
   
3. $1.51\times {10}^{12}$ per sec
   
4. $2.13\times {10}^{11}$ per sec

Q. Assertion : Kinetic energy of photo electrons emitted by a photosensitive surface depends upon the intensity of incident photon.

Reason : The ejection of electrons from metallic surface is possible with frequency of incident photon below the threshold frequency.

1. Assertion is true but reason is false.

2. Both assertion and reason are true but reason is not the correct explanation of the assertion.

3. Both assertion and reason are true and the reason is the correct explanation of the assertion.

4. Assertion and reason both are false.

5. Assertion is false but reason is true.

Q. In a system of equilibrium of charges, when a charged body $(+q)$ is displaced from its equilibrium position, the net force is
$[$Assume charges $+Q$ to be fixed and consider only axial displacement$]$

1. away from the original position
2. towards the original position
3. zero
4. Any of the option $a$ or $b$

Q. Draw graphs showing variation of photoelectric current with applied voltage for two incident radiations of equal frequency and different intensities. Mark the graph for the radiation of higher intensity.

Q.

What is Electromotive force?

Q. A hydrogen atom is in an excited state of principle quantum number $n$. It emits a photon of wavelength $\lambda$ when it returns to the ground state. The value of $n$ is $(\text{R is Rydberg constant)}$

1. $\sqrt{\lambda R(\lambda R-1)}$
2. $\sqrt{\frac{\lambda R-1}{\lambda R}}$
3. $\sqrt{\frac{\lambda R}{\lambda R-1}}$
4. $\sqrt{\lambda (R-1)}$

Q. If the intensity of the radiation on a photocell be increased four times, then the number of photoelectrons and the energy of photoelectrons emitted respectively become

1. four times, doubled
2. doubled, remains unchanged
3. remains unchanged, doubled
4. four times, remains unchanged

Q. In Bohr's atomic model, the electron is assumed to revolve in a circular orbit of radius $0.5\dot{\text{A}}$. If the speed of electron is $2.2\times {10}^6\text{m/s}$, then the current associated with the electron will be _____$\times {10}^{-2}\text{mA}$.
[Take $\pi$ as $\frac{22}{7}$]

Q. The radiation force experienced by body exposed to radiation of intensity $I$, assuming surface of body to be perfectly absorbing is

1. $\frac{\pi R^{2}I}{c}$
2. $\frac{\pi RHI}{c}$
3. $\frac{IRH}{2c}$
4. $\frac{IRH}{c}$

Q. What is a square law device and a bandpass filter, and write the frequency range of satellite communication. 😁

Q. When a brass plate is introduced between two charges, the force between the charges
A) decreases
B)increases
C)remains same
D)becomes zero

Q. In a photoelectric effect experiment, if 'f' is the frequency of incident radiation on the metal surface and 'I' is the intensity of the incident radiation, then

1. If 'f' is increased keeping 'I' and work function constant, saturation current increases.
2. If 'I' is increased keeping 'f' and work function contant saturation current increases.
3. If work function is decreased keeping 'f' and 'I' constant, then stopping potential increases but saturation current remains same.
4. On increasing distance between cathod and anode, stopping potential remains same.

Q. A photon of wavelength $\lambda$ incident on a free electron and is scattered in the backward direction. The fractional shift in its wavelength in terms of the Compton wavelength ${\lambda }_c$ of the electron is-

1. $\frac{{\lambda }_c}{2\lambda }$
2. $\frac{2{\lambda }_c}{3\lambda }$
3. $\frac{3{\lambda }_c}{2\lambda }$
4. $\frac{2{\lambda }_c}{\lambda }$

Q. if the velocity of an electron is doubled its de broglei frequency will ?? 1. halved 2. doubled 3. remain same 4 . four times

Q. The ratio of minimum wavelengths of Lyman and Balmer series will be

1. $1.25$
2. $5$
3. $4$
4. $0.25$

Q. Four charges equal to q are placed at the four corners of a rectangle of side a and $b(a\ne b)$ and a charge Q is at its centre. If the system is in equilibrium, then the value of Q is:

1. $-\frac{q}{4}(1+2\sqrt{2})$
2. $\frac{-q}{2}\left[\frac{a+b+\sqrt{a^2+b^2}}{\sqrt{a^2+b^2}}\right]$
3. $-q$
4. This system will never be in equilibrium

Q. A positively charged sphere of mass m=5kg is attached by a spring of force cons†an t K=10^4N/m. The sphere is tied with a thread so that spring is in its natural length. Another identical, negatively chatged sphere is fixed with floor, vertically below the positively charged sphere. If initial separation between sphere is r_0=50cm and magnitude of charge on each phere is q=100microcoulomb, calulate maximum elongation of spring when the thread is burnt. Take g=10m/s^2.

Q.

What is the relationship between light intensity and distance?

Q. Which one of the following is true in photoelectric emission

1. The threshold frequency depends upon the wavelength of incident light

2. Photoelectric current is directly proportional to the amplitude of light of a given frequency
3. Photoelectric current is directly proportional to the intensity of light of a given frequency at moderate intensities
4. Above the threshold frequency, the maximum K.E. of photoelectrons is inversely proportional to the frequency of incident light

Q. When an inert gas is filled in the place of vacuum in a photo cell, then

1. Photo-electric current is increased
2. Photo-electric current is decreased
3. Photo-electric current remains the same
4. Decrease or increase in photo-electric current does not depend upon the gas filled

Q. The incident intensity of light from the sun on a horizontal surface at sea level is about $1{\text{kW/m}}^2$. Assuming that $50\%$ of this light is reflected and $50\%$ is absorbed, the radiation pressure on this horizontal surface will be -

1. $5\times {10}^{-6}\text{Pa}$
2. $6\times {10}^{-6}\text{Pa}$
3. $7\times {10}^{-6}\text{Pa}$
4. $8\times {10}^{-6}\text{Pa}$

Q.

Show that the wavelength of electromagnetic radiation is equal to the de Broglie wavelength of its quantum (photon).

Q.

Explain the term electronics.