PHYSICS PAPER 3 - 2019 KCSE STAREHE MOCK EXAMS (QUESTIONS AND ANSWERS)

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INSTRUCTIONS TO CANDIDATES

  • You are supposed to spend the first 15 minutes reading the whole paper carefully before commencing your work.
  • Candidates are advised to record their observations as soon as they are made.
  • Marks are given for observation actually made, their suitability, accuracy and the use made of them. 

QUESTION 1
You are provided with the following apparatus

  • A Metre rule
  • A wire of length at least 100cm
  • A retort stand, boss and clamp.
  • A stop watch or stop clock
  • A micrometer screw gauge
  • An overflow can
  • A beaker at least 50ml or more.
  • A 50ml measuring cylinder
  • A piece of thread about 30cm
  • Water in a 250ml beaker
  • Two pieces of wood.
  • Mass labelled m.

You are required to follow the following procedure

  1.  
    1. Fill the overflow can with water to overflowing and then allow it to drain.
    2. Immerse the mass m into the can. Collect the overflow in a beaker as shown below in the figure below.
      phyc1regh
    3. Using the measuring cylinder provided determine the volume V of the water collected in the beaker. V =      cm3                 (1 mark)
    4. Calculate I given that I = phyc1ivregh (Where m=0.30 kg)                        (2 marks)
  2. Set up the apparatus as shown in figure 2 below. Ensure that the wire is free of kinks and the end tied to the hook is firm and the hook does not move. 
    phyc1bregh
  3. Adjust the length L, of the wire so that L = 70cm, Give the mass m, a slight twist such that when released it oscillates about the vertical axis as shown by the arrows in figure 2. Measure the time for twenty oscillations and record in Table 1.
  4. Repeat the procedure in (c) above for other values of L, as shown in Table 1. Complete the table.   (6 marks)
    Table 1

    Length L (cm)

    70

    60

    50

    40

    30

    20

    Length L (m)

               

    Time for 20 oscillations(s)

               

    Period T(s)

               

    T2 (S2)

               
  5. On the grid provided, plot the graph of T2 (S2) (y – axis) against L (m)        (5 marks)
  6. Measure the diameter d of the wire.     (1 mark)
    d = metres
  7.  
    1. Determine the slope of the graph.       (2 marks)
    2. Given that T2phyc1gfghre  where G is a constant, use the graph to determine the value of G.    (3 marks)

QUESTION 2
You are provided with the following apparatus

  • A metre rule
  • A screen fitted with cross-wires labelled O
  • A mounted white screen labelled S
  • A lump of plasticine
  • A candle
  • A plane mirror
  • Two lenses mounted on holder labelled L1 and L2 - pieces of cello tape.
    Proceed as follows:
    1. Arrange the apparatus as shown in the figure below so that the candle flame, the cross-wires and the centre of the lens lie on a straight line.
      phyc2ajklmn
    2. Adjust the position of the lens arrangement (lens, mirror and holder) until a sharp image of the cross-wires is observed on the screen O.
      Note: It might be necessary to adjust the position of the candle to make the image clearer. Measure the distance L1 between the screen and the centre of the lens L1
      L1 =......                                            (1 mark)
    3. Remove L1 and replace it with L2. Repeat procedure in (b) above to obtain distance, L2 between the screen and the centre of lens L2
      L2 =........                                  (1 mark)
    4. Now remove the mirror and arrange the apparatus as shown in figure below so that the two lenses, the cross-wires and candle flame lie on the straight line.
    5. Adjust the position of lens L1 so that the distance, d, is 5cm. (See figure below). Adjust the position of the screen S until a sharp image of the cross-wires is observed on the screen
      phyc2ejklmn
    6. Repeat the procedure in (f) above for values of, d, equal to 8cm, 12cm, 16cm and 20cm.

      Distance d (cm)

      5

      8

      12

      16

      20

      Distance v (cm)

               
    7. On the grid provided below, plot a graph of V(y-axis) against d. (5 marks)
    8. Determine the intercept Vo on the V-axis.
      VO =..........      (1 mark)
    9. Calculate constant F of the lenses using two methods.
      phyc2ijkmnl
    10. Calculate the power of lens L2 and state its SI unit. (3 marks)


MARKING SCHEME

  1.  
    1.  
      PHYC1VGHN 
    2.  

      Length L (cm)

      70

      60

      50

      40

      30

      20

      Length L (m)

      0.70

      0.60

      0.50

      0.40

      0.30

      0.20

      Time for 20 oscillations (s)

      61.01

      56.08

      51.36

      46.06

      39.81

      32.80

      Period T (s)

      3.051

      2.804

      2.568

      2.303

      1.991

      1.640

      T2 (s2)

      9.309

      7.862

      6.595

      5.304

      3.960

      2.690


      - Correct conversion of length L in M (1mk)
      - Time for 20 oscillation  (1/2mk for each value within range (maximum of 3mks)
      - Correct evaluation of period  (1mk)
      - Correct evaluation of T2 (1mk)    
    3. Axes:               Labelled with units  (1mk)
      Scale:               Simple and uniform  (1mk)
      Plotting:          Each correctly plotted point ( ½  mk) to a max To a max of 2mks (4points within 1 small square)
      Line:                Passing through at least 3 points correctly plotted  (1mk) 
      PHYC1GRAPH  
    4. d  = 0.34 x 10-3 = 3.4 x 10-4m               ü(1mk)
    5.  
      PHYC1GLPKJ

QUESTION 2

  1. L1 = 20.0 cm, L2 = 20.0 cm    (2mk)
  2. One mark given for each, a total of 5 marks
    Webp.net compress image 67
  3.  

    Distance d (cm)

    5

    8

    12

    16

    20

    Distance v (cm)

    11.5

    10.5

    9.5

    8.5

    7.5

  4. Vo = 13.0
  5.  
    1. Substitution (1mk)
      Evaluation (1mk)
    2. Substitution (1mk)
      Evaluation  (1mk)
  6. f = 20.0cm or 0.2 m
    Substitution with f being in metres  (1mk)
    Accuracy (1mk)
    Units  (1mk)
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