PHYSICS PAPER 3 - KCSE 2019 BAHATI MOCK EXAMINATION (WITH MARKING SCHEME)

QUESTION ONE
You are provided with the following apparatus

• A clean tap burette
• Retort stand
• Two clamps and 2 bosses
• A metre rule
• Water
• 100ml beaker
• A stop watch
  
  PROCEDURE

1. Clamp the burette and metre rule vertically and as close to each other as possible
2. Adjust the position of the burette so that its lower end is 15cm above the bench and place the 100ml beaker underneath it.
3. Fill the burette with water to a height above the 70cm mark of the metre rule as shown below.
   
4. By trial and error method adjust the rate of flow of the water until the time taken for the water to flow from 70cm mark to 65cm is between 25-30 seconds.
5. Once this flow rate has been achieved do not alter the flow rate for the rest of the experiment.
6. Fill the burette again with water to a level above the 72cm mark.
7. With the water level at the 70cm mark (at t=0) start the stop watch. Note the time taken for the height h of the water surface in the burette to decrease by 5cm;Do not stop the watch.
8. Continue to record the time taken for the height h of water surface to decrease by successive 5.0cm marks till you have 10 more readings.
9. Enter the results in the table below
10. Reset the watch and refill the burette .
11. Repeat the procedure to get second and third set of readings for t.(8marks)
    

    Height h(cm)	Trial 1		Trial 2	Mean time t
    70
    65
    60
    55
    50
    45
    40
    35

    
    
    1. Complete the table above and calculate the mean time t
    2. Plot a graph of height h (y-axis) against mean time t (5marks)
    3. Use your graph to determine the time taken for the height h to change from 64cm to 42cm. (2marks)
    4. Find the gradient of the graph when h is 47 cm 3mks

QUESTION 2
PART A
You are provided with the following:

• Lens
• Lens holder
• Metre rule
• Screen
• A 70cm long thread.
• Clamp, boss and retort stand.
• Small pieces of wood.
• Pendulum bob
  
  Proceed as follows:
• Using the provided thread, tie the marble to be used as a pendulum clamp the thread so that the length l of the pendulum to the centre of the marble is 50cm as in figure 2.
  
• Displace the marble slightly so as to oscillate along the vertical plane.
  1. Time and record the time, t, for 20 oscillations.
     t₁ = ___S            (1mk)
     t₂ = ___S            (1mk)
     t_ave=___S            (1mk)
  2. Calculate the period, T=___S                                                               (2mk)
  3. Calculate the frequency, f =___S                                                       (2mk)
  4. T²=__S                                                                                               (1mk)
  5. Convert L to metres, L= ___                                                               (1mk)
  6. Calculate       T²/_L   (1mk) 
  7. If the oscillation of the marble is given by the formula.   
         
     determine the value of g.                               (3mks)

PART B

1. Set up the apparatus as shown in figure 2 below. (ensure that the candle and the lens are in the line)
   
2. With the candle placed a distance L =100cm from the screen, determine the position of a magnified image of the candle on the screen by moving the lens
3. Determine the distance of the lens from the candle U₁
   U₁………………………. .cm                                                                               (1 mk)
4. Now move the lens towards the screen until you get a sharply focused diminished image. Determine the new distance of the lens from the candle U₂
   U₂………………………cm                                                                    (1 mk)
5. Calculate the displacement d of the lens                                                                                               (2 mk)
   d = U₂ — U₁ = …………………….cm
6. Give that λ = , calculate the value of λ (3 mks)
7. By using a distant object, find the focal length f of the lens                               (1mk)
8. compare the value in vi and vii                                                                            (1mk)

MARKING SCHEME

QUESTION 1
PART A

1 mark each row

1. h=64cm; t=30.0s
   h=42cm; t=210.0s
   Time taken= 210 - 30= 180s 
2. From the graph when h=35cm; t=290s
   gradient =  32-52               
   300-100
   = -20/200         
   =-0.1cms^-1      
   

QUESTION 2
PART A

1. t₁ = 28.44s­ +/- 3s
   t₂ = 29.50 s +/- 3s
   t_ave = 28.97 s
2. 20 oscillations = 28.97S
   1 oscillation = 1.448S              
   Period = T = 1.448s
3. f = 1/T
   =1/1.448
   =0.6906 Hz
4. T²=1.448²
   =2.097 s²
5. L = 50 cm = 0.5 m
6. T²/L = 1.448²/0.5
   =4.193s²m^-1            
7.  
    
   g= 9.418N/kg 

PART B

1. U= 36.0 cm  (1 mk)
2. U = 70.0 cm  (1 mk)
3. d²=70.0 – 36.0 = 34.0 cm     (1 mk)
4.  
    
   = 22.11 cm        (1 mk)
5. f=20.0cm +/-2cm (1mk)
6. λ = f , the focal length of the lens (1mk)