Physics Paper 2, May/June. 2014
 Questions: 1 2 3 4 5 6 7 8 9 10 11 12 Main

Weakness/Remedies
Strength

Question 12

(a)     Write Einstein’s photoelectric equation and identity each component of the equation

(b)      For a photocell, state one factor each that is responsible for the:

1. emission;
2. rate of emission;
3. energy of photoelectrons.

(c)      (i)    Two nuclear equations are given below:
+    ……………………..equation A
+    ……………………..equation B
Determine the values of:
(   p and q in equation A;
(β)   m  and n in equation B and identify X.
(ii)   Give a reason why it is important to dispose of radioactive waste safety.
(d)   (i)    A certain atom emits ultra-violet photon of wavelength 2.4 x 10-7m
Calculate the energy of the photon.

-6.0 x 10-19J

(ii)

-8.2 x 10-19J

-8.8 x 10-19J

-16.7 x 10-19J

Diagram correctly copied with relative gaps
Arrow correctly shown
(ii)   The figure above illustrates the energy levels of the atom.  Copy the figure in your
answer booklet and indicate on it, the energy level transitions which cause the emission
of the photon in 13(d)(i) above.
[h  =  6.6 x 10-34 Js;  c = 3.0  x  108 ms-1]

_____________________________________________________________________________________________________
Observation

Part (a)  This question was the least popular among the candidates.  The equation was not clearly written by many candidates.  Hence the identification of the component was incomplete.
Part(b)   Performances by candidates was below average because of ignorance.
Part(c)  Performances was above average.  The candidates performed very well because they understood the concept very well.
Part(d)  Performance was average.  However, some candidates, were unaware of the need to consider the relative gaps between the lines.  Most candidates indicated correctly the arrow on the transition line, few, forget to insert arrows on the line where necessary because they were ignorant of the concept.
The expected answers are:
12.  (a)    Einstein’s Photoelectric Equation

E    =   W  +  K.Emax
E    =   Energy of incident radiation
W   =   Work function
K.E =  Maximum kinetic energy of photoelectron

(b)    (i)  -  Emission – frequency/wavelengh  of incident radiation
(ii) -   Rate of emission -  intensity of incident radiation/ number of photons
(iii) -   Energy of photoelectrons - frequency/wavelengh of incident radiation

(c)    (i)   (     218  +  q   =      222
q        =    4
(β)       p   =  84  +  2    =    86
m   =   214  -  214   =  0
n    =    83 – 84  =   -1

X    is an electron/ beta particle

(ii)    Safety Disposal of Radioactive waste

e.g  It is   -   toxic
-   emits harmful radiations

(d)(i)      E   =   hf  =
=       =  8.25 x 10-19

=    8.3 x 10-19J

-8.8 x 10-19J

-6.0 x 10-19J

-8.2 x 10-19J

-16.7 x 10-19J

(ii)

Diagram correctly copied with relative gaps
Arrow correctly shown