Physics Paper 2, Nov/Dec. 2009

Physics Paper 2, Nov/Dec. 2011

Questions:	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	Main

General Comments
Weakness/Remedies
Strength

Question 7

The table shows the pointer reading of a spring balance when different weights are hung on it.
Determine the value of F.

Weight/N	5	10	F
Pointer reading/cm	8	12	30

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comments

     Candidates performance in this question was poor. Most of them could neither state the
     similarities nor the differences between photoeletronic emission and thermionic emission.
    The expected answers are:
    (a)     Differences between thermionic and photoelectric emission

Thermionic emission

Photoelectric emission

- Caused by heat/themalenergy

- Electrons are released at a
particular temMany candidates attempted this question and majority of them faired very well in it.

The expected answer is:
.         F = ke
            10 – 5 = k(12 – 8)                        ……..(A)
            F – 10 = k(30 – 12)                      ……..(B)
            Solving simultaneously equations   (A) and (B)

F = 32 . 5N

perature
-    Time rate of emission of
     electrons increases with
     increase in temperature

Caused by lightelectromagnetic wave energy
Electrons are released at threshold frequency
Time rate of emission of electrons increases with/is proportional to increase in intensity

      (b)    Similarities between thermionic and photoelectric emission

both are surface phenomena
electrons are released in both cases
ejected/emitted electrons have kinetic energy.