KCSE 2014 Physics Paper 3 Questions with Marking Scheme

QUESTION 1

You are provided with the following:

• a voltmeter
• a milliammeter
• a micrometer screw gauge (to be shared)
• a stopwatch
• a centre zero galvanometer
• a switch
• ten connecting wires (at least with a crocodile clip on one end)
• a resistance wire mounted on a millimetre scalelabeled AB
• a resistance wire labeled P
• a resistance wire labeled Q
• a capacitor labeled C
• a metre rule or half metre rule
• two dry cells and a cell holder
• a carbon resistor labeled R
  
  

Proceed as follows:

PART A

1. Using the micrometer screw gauge provided, measure the diameter:
   1. D of wire P.
      D = _________________ (1 mark)
   2. d of wire Q
      d = _________________ (1 mark)
      
      
2. Determine C₁ the value of the ratio D/d
   C₁ = __________________ (1 mark)
   
   
   1. Set up the circuit as shown in figure 1. (Ensure that each of the wires P and Q is 50 cm long)
      
      
      
      Close the switch. Using the clip at the the free end from the wire from the galvanometer, tap wire AB near end A and observe the defection in the galvanometer.
      
      
   2. Then tap the wire near end B and then observe the deflection in the galvanometer.
   3. Now tap the wire AB at various points between A and B to obtain a point K where there i no deflection in the galvanometer.
      1. Determine the length L₁, the distance from A to K.
         L1 = ________________ (1 mark)
      2. Determine the length L₂, the distance from B to K.
         L₂ = ______________ (1 mark)
         
         
   1. Given that resistance R_Q of Q is 9.0 ohms, determine the resistance R_P of P using the expression: (2 marks)
      
      
      
      
   2. Determine the value of C₂ given that, (2 marks)
      
      
      
      
   3. Compare the value of C₁ (in part (b)) with that of C₂. (1 mark)
      PART B
      
      
3. Set up the circuit shown in figure 2. S and T are crocodile clips.
   
   
   
   
   1. Charge the capacitor C by connecting the crocodile clip to S. Record the reading of the voltmeter, V
      V = _____________ (1 mark)
      
      
   2. Calculate the value of current of I_o , given that I_o = V/R (where R = 4.7 x 10³ Ω) (3 marks)
      
      
   1. Discharge the capacitor by by disconnecting the crocodile clip from S and connecting it to T. Observe and record the highest reading of the milliammeter I₁. (This is the current at t₀ = 0).
      (You may have to repeat the process to obtain an accurate value.)
      I₁ = _______________ (1 mark)
      
      
   2. Recharge the capacitor by connecting the crocodile clip to S.
      
      
   3. Discharge the capacitor and at the same time start the stop watch to measure the time t₁ taken for the current to decrease to the half the value of I₁  ie (¹/₂I₁)
      t₁ = ______________ (1 mark)
      
      
   1. Recharge the capacitor and repeat the procedure in f(iii) to measure the time t₂ taken for the the current to decrease to one tenth of the value of I₁  i.e (¹/₁₀I₁)
      t₂ = _____________ (1 mark)
   2. Use the values of the currents corresponding times to draw a graph of current I (y axis) on the grid provided. (3 marks)
      
      

QUESTION 2
You are provided with the following:

• a stand boss and clamp
• two wooden blocks
• a stopwatch
• a half metre rule or metre rule
• a metallic rod
• a bare copper wire labelled M attached to a crocodile clip
• a bare copper wire labeled N attached to a crocodile clip
  
  Proceed as follows:

1. Clamp wire M between the wooden blocks so that the length l of the wire between the wooden blocks and the point of its attachment on the crocodile clip is 5 cm. Clamp the metallic rod at its mid-point using the crocodile clip attached to wire M.
   
   
2. Displace the rod through a small angle in a horizontal plane aboutits mid point so thst when released, it oscillates in the same plane. Record the time t for 10 oscilations and determine the period T in Table 1.
   
   
3. Repeat part (b) for the other lengths of wire M shown in Table 1.
   
   
4. Complete Table 1. (6 marks)
   
   
   
   
5. Plot a graph l (y axis)against T².
   
   
6. Determine the gradient of the graph, S. (3 marks)
   
   
7. Now replace wire M with wire N in the set up.
   
   1. For l = 20 cm, displace the rod through a small angle in the horizontal plane and measure the time t_N for ten oscillations.
      t_N = __________ (1 mark)
   2. Determine the period T_N = ____________ (1 mark)
   3. Calculate T_N² (1 mark)
   4. Determine the value of H given that  (1 mark)
   5. Calculate the value of ^H/_S (2 marks)

MARKING SCHEME

QUESTION ONE PART A

1.                  
   1. D = 0.38 mm ± 0.02 (1 mark)
   2. d = 0.28 mm ± 0.05 (1 mark)
2. C₁ = D = 0.38 = 1.357 (1 mark)
           d    0.28
3.                        
   1. L₁ = 38.5 cm (1 mark)
      L₂ = 61.5 cm (1 mark)
      (l₁ < l₂)
      R_p = 38.5
      9      61.5
      therefore: R_p = 5.63Ω
      C₂ = √  9  
                5.63
      = 1.264   (2 marks)
   2. C₁ and C₂ are nearly equal (to the nearest whole number).(1 mark)

QUESTION ONE PART B

V = 3.1 volts ± 0.1
I0 = V  =      3.1      A
       R      4.7  × 10³
= 0.659 mA   (3 marks)
I₁ = 0.63 mA
For = I₁
         2
t₁ = 3.9 s(1 mark)
For = I₁
        10
t₂ = 13.5 s (1 mark)

(3 marks)

QUESTION TWO
(d)

(6 marks)
(e) Graph.

(5 marks)
(f) Gradient = 20 cm/s² 
                     16
= 0.20 cm/s²
    16
= 0.015625 ms^-2   (3 marks)
(g) l_N = 20 cm = 0.2 m

1. t_N = 52.0
2. T_N = 5.2
3. T_N² = 27.04(1 mark)
   H =   0.2    = 0.007396 (1 mark)
          27 04
4. H = 0.007396
   S    0.015625
   = 0.4737     (2 marks)