Work Function

Q. If an electron recieves 10eV. energy and wastes 3 eV in overcoming the work function then find the potential that will stop the electron from striking the collector plate.

1. 7 V
2. 5 V
3. 3 V
4. 10 V

Q. A metal surface is illuminated by light of two different wavelengths ${\lambda }_1=500\text{nm}$ and ${\lambda }_2=620\text{nm}$. The maximum speed of ejected photoelectrons corresponding to these wavelengths are in the ratio $3:2.$ Then work function of the metal in $\text{milli eV}$ is approximately equal to .
$(hc=1240\text{eV – nm})$

Q.

If work function of a metal is 2 eV, it means every electron requires only 2 eV to get ejected from the metal surface.

1. True

2. False

Q.

A metal with work function of 3.7 eV is being used in a photoelectric experiment. A light source is switched on and light is allowed to fall on the plate such that it delivers 10 eV to each electron. Find the kinetic energy with which the electrons will come out?

1. 7.3 eV

2. (0 - 6.3 ) eV

3. None of these

4. 6.3 eV

Q.

Sodium has a work function of 2.28 eV. Let's say, I introduce a very strong external electric field, which is applying a force on the electrons outwards, thus giving them electrical potential energy of 1.5 eV each. What is the work function of the metal surface in such a case?

1. 0.78 eV

2. 1.5 eV

3. 2.28 eV

4. 0 eV

Q. The work function for aluminium surface is 4.2 eV and that for sodium surface is 2.0 eV. The two metals were illuminated with appropriate radiations so as to cause photoemission. Then choose the correct statement.

1. Both aluminium and sodium will have the same threshold frequency.
   
2. The threshold frequency of aluminium will be more than that of sodium.
   
3. The threshold frequency of aluminum will be less than that of sodium.
   
4. Cannot say

Q. No photoelectrons are emitted from a metal if the wavelength of light exceeds $6000\stackrel{\circ }{A}$. The work function of the metal is approximately equal to

1. $3\times {10}^{-16}J$
2. $3\times {10}^{-19}J$
3. $3\times {10}^{-20}J$
4. $3\times {10}^{-22}J$

Q. A metal has a work function of $2.5\times {10}^{-19}J.$The threshold frequency beyond which photo electrons will come out is.

1. $2.3\times {10}^{14}Hz$
2. $3.3\times {10}^{14}Hz$
3. $2.8\times {10}^{14}Hz$
4. $3.8\times {10}^{14}Hz$

Q.

$\begin{array}{cc}ColumnI& ColumnII\\ \text{(A) If v (frequency) is increased keeping}\text{I (intensity) and}\Phi \text{(work function) constant}& \text{(P) Stoping potential increases}\\ \left(B\right)\text{If I is increased keeping v and}\Phi \text{constant}& \text{(Q) Saturation photocurrent increases}\\ \text{(C) If the distance between anode and cathode increases.}& \text{(R) Maximum KE of the photoelectrons increase}\\ \text{(D) If}\Phi \text{is decreased keeping v and I constant}& \text{(S) Stopping potential remains the same}\end{array}$

1. (A) (P, R); (B) (Q, S); (C) (S); (D) (P, R)

2. (A) (Q, S); (B) (P, R); (C) (S); (D) (P, R)

3. (A) (P, R); (B) (Q, S); (C) (P, R); (D) (S)

4. (A) (P, R); (B) (S); (C) (Q, S); (D) (P, R)

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

1. 540 nm
2. 310 nm
3. 220 nm
4. 400 nm