Physics Paper 3 Questions and Answers with Confidential - Asumbi Girls High School KCSE Mock 2021

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Questions

Instructions to candidates

  • Answer ALL the questions in the spaces provided in the question paper.
  • You are supposed to spend the first 15 minutes of the 2 ½ hours allowed for this paper reading the whole paper carefully before commencing your work.
  • Marks are given for a clear record of the observations actually made, for their suitability and accuracy and the use made of them.
  • Candidates are advised to record their observations as soon as they are made.
  • Mathematical table and electronic calculators may be used.

 

  1. You are provided with the following apparatus
    • A metre rule
    • Two stands
    • A pendulum bob
    • Some plasticine
    • Stop watch
    • Protractor
    • Two pieces of strings (long and short one)

      Proceed as follows:
      1. Attach one end of the length of string to the metre rule at 10cm mark. Mark by use of a sliding loop of string round the meter rule.
      2. Fix the string at this point with the small bob of plasticine.
      3. Tie the string in a second loop at 90cm mark so that the string is stretched taught between the two marks.
      4. Fix this loop with a small plasticine. Attach the pendulum bob to the centre of the string so that the centre of gravity is 15cm below the point of suspension.
      5. If the attachments of the pendulum bob to the pieces does not produce a V-shape squeeze the string at the knot between the thumb and the fore finger.
        05PhycPP3q1e
        1. Measure the angle 2
        2. Pull the pendulum bob towards you through a small distance, release it; measure the time (t) of the motion by timing 10 oscillations.
        3. Remove the plasticine at B and slide the loop towards A by 4cm and repeat (ii) above for other distances AB as shown in the table below.

          RESULTS (9 marks)
          Length from A to B(cm) 80 76 72 68 64 60
          Time for 10 oscillations(s)            
          Periodic time T(s)            
          T2(s2)            
          2θ            
          θ            
          Cos Î¸            
      6. Plot a graph of T2 against Cos (5 marks)
      7. Find the slope S of the graph. (3 marks)
      8. Given that , s= 1.6π2/k find k (3 marks)
  2.        
    PART A
    1. You are provided with the following apparatus
      • a glass block
      • a plane mirror
      • 4 optical pins
      • a soft board
      • A cellotape ( about 15cm long)
      • 2 white – plain sheets of paper
      • a ruler or half metre rule
      • a protractor
      • 4 office pins

        Proceed as follows:-
        1. Using the cello tape provided fix the plane mirror to the glass block alongside as shown in the figure below. The reflecting surface to face the glass block.
          05PhycPP3q2Aa
        2. With the use of the office pins, secure firmly a white plain paper on the board and place the block together with attached mirror.
        3. Draw the outline of the glass block together with the mirror
        4. Remove the block and the mirror and draw a normal at B somewhere a quarter- way the length of the outline you drew in (iii) above.
        5. Draw four(4) different rays AB incident at B and extended to C. The incident rays should make angles 10°, 20°, 30°,and 40°.
        6. Replace the glass block together with the attached mirror so as exactly fit the outline in(iii)
        7. Place two object pins P1 and P2 along the 10 line. Locate the images of pinsP1 and P2 as they appear by non-parallax (the images of the pins appear to be in a straight line when viewed through the glass block).
          Place pins P3 and P4 so that the images of pins P1 and P2 are not seen.
        8. Remove the glass block together with the attached mirror from the outline and produce the lines joining P1 to P2 and P3 to P4 so that the they intersect at C. Measure and record the distance x in the table 2 below. (4 marks)
          NB. It may be necessary for you to draw another outline so as to avoid congestion of (construction) lines.
           Angle i Â° 10 20 30 40
          Distance x(cm)        
          Table 2
        9. Now measure the breadth b of the glass block.
          b=______________________________________________________(1mark)
        10. Calculate the average Ax of the values of x in table 3 above
          Ax ____________________________________________________ (1mark)
        11. Determine the refractive index of the glass block using the formula.
          Refractive index n of glass n=b/Ax (2 marks)

PART B
You are provided with the following

  • A nichrome wire 1m long mounted on a scale
  • A dry cell
  • 1 ammeter ( 0 – 1A)
  • A switch
  • A bulb
  • A voltmeter ( 0-5v or 0 – 3v)
  • A one cell holder
  • At least 6 connecting wires, one with a jockey

    Proceed as follows
    1.          
      1. Set up the circuit as shown in fig. 2
        05PhycPP3q2Ba
      2. With the jockey / crocodile clip at B (L=100cm) note the voltmeter reading V and ammeter reading, I and record on the table III below.
      3. Repeat the procedure in (ii) above for L=80cm, 60cm, 40cm, 20cm and 0cm and record. 5 marks
        Table III
        L(cm) 100  80  60  40  20  0
        V(volts)            
        I (A)            
      4. Plot the graph of V(y-axis) against I on the grid provided. 5marks
      5. Calculate the slope of your graph when current is 0.15A. 2 marks

Confidential 

Question 1
Each candidate is required to have:

  • A metre rule
  • Two stands
  • A pendulum bob
  • Some plasticine
  • Stop watch
  • Protractor
  • Two pieces of strings (long~1m and short ~20cm one)

Question 2
Each candidate is required to have:

  • A glass block (10 cm x 6 cm)
  • A Plane mirror (7cm x 6 cm)
  • 4 optical pins
  • A soft board
  • Cellotape (about 15 cm long)
  • 2 white – plain sheets of paper
  • a ruler or half – metre rule
  • A protractor
  • 4 office pins
  • a nichrome wire, 1m long mounted on mm scale and labeled AB at the ends (SWG 28)
  • A dry cell
  • 1 ammeter ( 0 – 1A)
  • A switch
  • A bulb
  • A voltmeter ( 0-5v or 0 – 3v)
  • A one cell holder
  • At least 6 connecting wires, one with a jockey

Marking Scheme

  1.         
    1.           
    2.       
    3.     
      Length from A to B(cm) 80 76 72 68 64 60
      Time for 10 oscillations(s) 10  11  12  13  14  15
      Periodic time T(s)  1.0  1.1  1.2  1.3  1.4  1.5
      T2(s2)  1.00  1.21  1.44  1.69  1.96  2.25
      2θ  150°  138°  130°  108°  104°  96°
      θ  75°  69°  65°  54°  52°  48°
      Cos Î¸  0.2588  0.3883  0.4226  0.5878  0.6157  0.6691

      1.  
        05PhycPP3qa1f
      2. Slope, S= Î´Y/δX
        (20 x10-2, 0.375), (75 x 10-2, 2.0)
        S=       2.0 - 0.375       = 2.95
                (75-20) x 10-2
      3. S= 1.6π2 
                k
        k= 1.6π2  = 5.353
             2.95
  2.    
    PART A
    1.      
      1.           
         Angle i Â° 10 20 30 40
        Distance x(cm)  5.2  4.5  3.9  3.4
               
      2.  b = 6.2 cm
      3. Ax = 4.25 cm
      4. Refractive index = 6.2 = 1.45 ± 0.05

PART B       

  1.         
    1.    
      L(cm) 100  80  60  40  20  0
      V(volts) 0.5 - 0.7
      0.08 - 0.12
       0.6 - 1.0
      0.13 - 0.17
       0.7 - 1.1
      0.18 - 10.22
      0.8 - 1.2
      0.33 - 0.37
      0.9 - 1.3
      0.68 - 0.72
       1.1 - 1.5
      1.23 - 1.27
      I (A)  0.12 - 0.16
      0.04 - 0.08
       0.14 - 0.18
      0.06 - 0.10
       0.15 - 0.19
      0.08 - 0.12
       0.16 - 0.20
      0.12 - 0.16
       0.17 - 0.21
      0.14 - 0.18
       0.18 - 0.22
      0.16 - 0.20
       Try both tables and use the one that gives advantage to the candidate . For each correct value / entry give ½ for a maximum of 5 for both v and I
      Total (5mrks)

    2. Axes :- should be well labeled with correct units
      Scale :- Simple and uniform
      Plotting : correct should be smooth and passing through at least 3 correctly plotted points within 1 small square

      N/B curve should be continuous
      Total (5mrks)

    3. For drawing a tangent at I = 0.15A
      Slope =    ΔV   
                      ΔI
         0.85 - 0.65     ½ correct intervals from tangent
           0.175 – 0.13
      = 4.4444 V/A
      Or 4.4444 Ω For correct evaluation to 2 d.p rounded or truncating
      ½ For units
      N/B if curve is wrong
      i.e Co, this part is awarded zero.
      05PhycPP3qa2a
  2. x = 1.5 – 2.0 cm 1 to 1 d.p

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