Stopping Potential vs Intensity

Q. An electron falls from rest through a vertical dis†an ce h in a uniform and vertically upward directed electric field E. The direction of electric field is now reversed, keeping its magnitude the same. A proton is allowed to fall from rest in it through the same vertical dis†an ce h . The time of fall of the electron, in comparison to time of fall of the proton i

Q. A uniform electric field E Exists between two metal plates one negative and other positively charged . The plate length is l and the seperation of the plates is d . An electron and a proton start moving parallel to the plates towards the other e from the mid point of the seperation of plates at one end of the plates . Which of the two will have greater deviation when they come out of the plates if they start with 1) same initial velocity 2)same initial kinetic energy 3)same initial momentum

Q. The surface of a metal is illuminated with the light ofWavelength 400 nm. The kinetic energy of theejected photoelectrons was found to be 1.68 eV.Work function of the metal is about(1) 3.09 eV(3) 4.73 ev(2) 1.42 eV(4) 0.68 ev

Q. When light of a given wavelength is incident on a metallic surface, the minimum potential needed to stop the emitted photoelectrons is $6.0\text{V}$. This potential drops to $0.6\text{V}$ if another source with wavelength four times that of the first one and intensity half of the first one is used. What are the wavelength of the first source and the work function of the metal, respectively?
$[\text{Take}\frac{hc}{e}=1.24\times {10}^{-6}{\text{JmC}}^{-1}.]$

1. $3.78\times {10}^{–7}\text{m},1.20\text{eV}$
2. $3.78\times {10}^{–7}\text{m},5.60\text{eV}$
3. $1.72\times {10}^{–7}\text{m},1.20\text{eV}$
4. $1.72\times {10}^{–7}\text{m},5.60\text{eV}$

Q. 13.A current passes through a resistor. Lets K1 and K2 represent the average kinetic energy of the conduction electrons and the metal ions respectively. How to compare k1 and K2

Q.

When the light source is kept 20 cm away from a photo cell, stopping potential 0.6 V is obtained. When source is kept 40 cm away, the stopping potential will be

1. 2.4 V

2. 0.3 V

3. 0.6 V

4. 1.2 V

Q. A beam of cathode rays after gaining kinetic energy once it passes throught a potential difference of $V$ is subjected to crossed electric ($E$) and magnetic fields ($B$). The fields are adjusted such that the beam is not deflected. The specific charge of the cathode rays is given by

1. $\frac{B^2}{2V{E}^2}$
2. $\frac{2V{B}^2}{E^2}$
3. $\frac{2V{E}^2}{B^2}$
4. $\frac{E^2}{2V{B}^2}$

Q. The work function for the following metals is given: Na: 2.75 eV; K: 2.30 eV; Mo: 4.17 eV; Ni: 5.15 eV. Which of these metals will not give photoelectric emission for a radiation of wavelength 3300 Å from a He-Cd laser placed 1 m away from the photocell? What happens if the laser is brought nearer and placed 50 cm away ?

Q. The curves a, b, c and d shows the variation between the applied potential difference $\left(V\right)$ and the photoelectric current $\left(i\right)$ at two different intensities of light $(I_1>I_2)$. Which of the following figure is correct?

1. 
2. 
3. 
4. 

Q. An experimental setup for verification of photoelectric effect is shown in the diagram. The voltage across the electrodes is measured with the help of an ideal voltmeter, and it can be varied by moving jockey $J$ on the potentiometer wire. The battery used in potentiometric circuit is of $20\text{V}$ and its internal resistance is $2\Omega$. The resistance of $100\text{cm}$ long potentiometer wire is $8\Omega$.


The photo current is measured with the help of an ideal ammeter.

The wavelength of various colours is as follows:

$\text{Violet}:4000\mathring{A}-5000\mathring{A}$
$\text{Blue}:4500\mathring{A}-5000\mathring{A}$
$\text{Green}:5000\mathring{A}-5500\mathring{A}$
$\text{Yellow}:5500\mathring{A}-6000\mathring{A}$
$\text{Orange}:6000\mathring{A}-6500\mathring{A}$
$\text{Red}:6500\mathring{A}-7000\mathring{A}$

It is found that the ammeter current remains unchanged $\left(2\mu \text{A}\right)$ even when the jockey is moved from the end $\text{P}$ to the middle point of the potentiometer wire. Assuming one photon ejects one electron and the power of the light incident is $4\times {10}^{-6}\text{W}$, the colour of the incident light is:

1. $\text{Green}$
2. $\text{Violet}$
3. $\text{Red}$
4. $\text{Orange}$

Q. When the light source is kept 20 cm away from a photo-cell, stopping potential of 0.6 V is obtained. When source is kept 40 cm away, the stopping potential will be

1. 0.3 V

2. 0.6 V

3. 1.2 V

4. 2.4 V

Q.

Light of wavelength $\lambda$ falls on a metal having work function $h_c$ / ${\lambda }_0$​. The photoelectric effect will take place only if

1. $\lambda \le {\lambda }_0$

2. $\lambda \ge 2{\lambda }_0$

3. $\lambda <\raisebox{1ex}{${\lambda }_0$}\!\left/ \!\raisebox{-1ex}{$2$}\right.$

4. $\lambda \ge {\lambda }_0$

Q. The photoelectric cut-off voltage in a certain experiment is 1.5 V. What is the maximum kinetic energy of photoelectrons emitted?

Q. If the frequency of light in a photoelectric experiment is doubled, the stopping potential will
(a) be doubled
(b) be halved
(c) become more than double
(d) become less than double

Q. In a photoelectric experiment, the collector plate is at 2.0 V with respect to the emitter plate made of copper (φ = 4.5 eV). The emitter is illuminated by a source of monochromatic light of wavelength 200 nm. Find the minimum and maximum kinetic energy of the photoelectrons reaching the collector.

Q. The curves a, b, c and d shows the variation between the applied potential difference $\left(V\right)$ and the photoelectric current $\left(i\right)$ at two different intensities of light $(I_1>I_2)$. Which of the following figure is correct?

1. 
2. 
3. 
4. 

Q.

When a point source of light is at a distance of one metre from a photo cell, the cut off voltage is found to be V. If the same source is placed at 2 m distance from photo cell, the cut off voltage will be

1. $V$

2. $\frac{V}{2}$

3. $\frac{V}{4}$

4. $\frac{V}{\sqrt{2}}$

Q. In photoelectric effect, the slope of the straight line graph between stopping potential and frequency of the incident light gives the ratio of Planck's constant to

1. Work function
2. K.E. of electron
3. Charge of electron
4. Photoelectric current

Q. Kirchhoff's law of meshes is in accordance with law of conservation of:

1. charge
2. energy
3. current
4. angular momentum

Q. The stopping potential in a photoelectric experiment is linearly related to the inverse of the wavelength (1/λ) of the light falling on the cathode. The potential difference applied across an X-ray tube is linearly related to the inverse of the cutoff wavelength (1/λ) of the X-ray emitted. Show that the slopes of the lines in the two cases are equal and find its value.

Q. The curves a, b, c and d shows the variation between the applied potential difference $\left(V\right)$ and the photoelectric current $\left(i\right)$ at two different intensities of light $(I_1>I_2)$. Which of the following figure is correct?

1. 
2. 
3. 
4. 

Q. The maximum intensity produced by two coherent waves of intensity $I_1$ and $I_2$ will be

1. $I_1+I_2$
2. $I_1^2+I_2^2$
3. $I_1+I_2+2\sqrt{I_1{I}_2}$
4. zero

Q. The curves a, b, c and d shows the variation between the applied potential difference $\left(V\right)$ and the photoelectric current $\left(i\right)$ at two different intensities of light $(I_1>I_2)$. Which of the following figure is correct?

1. 
2. 
3. 
4. 

Q. 50% of the X-rays coming from a Coolidge tube are able to pass through a 0.1 mm thick aluminium foil. If the potential difference between the target and the filament is increased, the fraction of the X-rays passing through the same foil will be
(a) 0%
(b) < 50%
(c) 50 %
(d) > 50%

Q. 21.If an electron enters in to a space between the plates of a parallel plates capacitor at an angle alpha with the plates and leaves at an angle Beeta to the plates. The ratio of its K.E while entering the capacitor to that while leaving will be

Q.

A photo electric setup uses a 100 watt bulb of blue colour. If I bring the bulb closer to the plate what will happen to the stopping potential and why? According to classical model, it will become more ___________ (positive/negative)

1. Positive

2. Negative

Q. According to the wave model, energy of the light falling on the plate depends only on the amplitude of light and not on frequency.

1. True
2. False

Q. An electron is projected horizontally with a kinetic energy of 10 keV. A magnetic field of strength 1.0 × 10⁻⁷ T exists in the vertically upward direction. (a) Will the electron deflect towards the right or left of its motion? (b) Calculate the sideways deflection of the electron while travelling through 1 m. Make appropriate approximations.

Q. The stopping potential for photoelectrons from a metal surface is $V_1$ when monochromatic light of frequency $v_1$ is incident on it. The stopping potential becomes $V_2$ when monochromatic light of another frequency is incident on the same metal surface. If $h$ be the Plancks onstant and $e$ be the charge of an electron, then the frequency of light in the second case is

1. $v_1-\frac{e}{h}(V_2+V_1)$
2. $v_1-\frac{e}{h}(V_2-V_1)$
3. $v_1+\frac{e}{h}(V_2-V_1)$
4. $v_1+\frac{e}{h}(V_2+V_1)$

Q.

When a point source of light is at a distance of one metre from a photo cell, the cut off voltage is found to be V. If the same source is placed at 2 m distance from photo cell, the cut off voltage will be

1. $V$

2. $\frac{V}{2}$

3. $\frac{V}{4}$

4. $\frac{V}{\sqrt{2}}$