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 Physics Paper 1, MAy/June. 2008
 Questions: 1 2 3 4 5 6 Main

Weakness/Remedies
Strength

Question 3

(a)You are provided with two resistance wires labeled A and B, a 1 Ω standard resistor Rx and other necessary apparatus.

(i)         Connect  Rx in the left hand gap of the metre bridge, a length L = 100 cm  of wire
A in the right hand gap and the other apparatus as shown in the diagram above.

(ii)        Determine and record the balance point P on the bridge wire NQ.

(iii)       Measure and record lx  =  NP and lx   =  PQ.

(iv)      Evaluate  R1   =  ly        Rx.
lx
(v)        Repeat procedure for four other values of L =  95, 85, 75, and 65 cm. In each
case, determine and record the balance point P and the lengths lx and ly .  Also
evaluate R1.

(vi)      Repeat the experiment with the second wire B.  Obtain the balance points P and
the values of  lx and ly.

(vii)     Evaluate R2  =     ly  Rx in each case.  Tabulate your readings.
l
(ix)      Plot a graph of R2 on the vertical axis against R1 on the horizontal axis.

(x) Determine the slope, s, of the graph.
(xi)     Evaluate k  =   √ s.

(xii)   State two precautions taken to obtain accurate results.                             [21 marks]

(b)

(i)     State two advantages of using a potentiometer over a voltmeter for
measuring potential difference.                                                     [2 marks]

(ii)        Define internal resistance of a cell.                                                 [2 marks]

_____________________________________________________________________________________________________
Observation

The candidates were required to

(i)       connect a circuit as shown in the diagram above:
(ii)      measure five values of lx and ly for wire A to at least 1 decimal place
in trend. Trend: as L decreases, lx increases.
(iii)     measure five values of  lx and ly  for wire B to at least 1 decimal place and
in trend.  Trend: as L decreases, lx increases.

(iv)     evaluate five values of R1  and  R2 correct to 2 decimal places.

(v)     present data on a composite and complete table showing L, lx, (A), lY (A), lx
(B),  lY B, R1 , R2.

(vi)     correctly distinguish the graph axes, select reasonable scales, plot the five
points correctly and draw a line of best fit into the points;

(viii)     draw a large right angled triangle on the graph line, read ∆R2 and ∆R,
and evaluate slope    =  ∆R²

∆R¹

(ix)     Evaluate k  =   √s.

(x)      State any two of the following precautions in acceptable form of speech:

-     Key removed when not taking readings:
-     Ensured tight connections/clean terminals;
-     Avoided parallax errors in reading meter rule;
-     Jockey not allowed to scratch resistance wire;
-     Zero error of metre rule noted and corrected;

b (i)  Any two correct advantages potentiometer over the voltmetre e.g

-     High accuracy
-     Null deflection (does not draw current at balance point)
-     Range can be increased as required
-     No friction in moving parts.

(ii)The internal resistance of a cell is the opposition to the current flow through [the electrolyte of] the cell.

This question was very popular and well attempted by many candidates.  Some candidates however had difficulty in making deductions from the graph.  Some failed to record initial ammeter readings as demanded by the question.

Part b was fairly attempted.