KCSE 2018 Physics Paper 3 with Marking Scheme

QUESTIONS

Question 1
You are provided with the following:

• Some water in a container
• A 10ml measuring cylinder
• A piece of a glass rod
• A 10g mass
• 5 paper clips
• A half metre rule
• A metre rule
• Two stands, two bosses and two clamps
• Three pieces of sewing thread

Proceed as follows:

1. Pour 6 ml of the water into the measuring cylinder. Lower the glass rod into the water and determine the volume V of the glass rod.
   V = ....................................................... cm (1 mark)
   Remove the gless rod from water.
2. Using a stand and a piece of string, suspend the half metre rule at its centre of gravity C so that it balances horizontally with the scale facing you.
   Using a second stand, clamp a metre rule vertically near one end of the half metre rule to note the height at which the half metre rule is horizontal.
   Maintain this height throughout the experiment
   Record the centimetre mark of the centre of gravity C.
   C = .......................................... cm (1 mark)
3. Using the string, suspend the 10g mass on the half metre rule at a distance d = 2 cm from C. The distance d = 2 cm should be maintained throughout the experiment.
   Balance the half metre rule by suspending the glass rod using a string at a distance X from C.
   Record the value of X
   X  = .............................................................. cm (1 mark)
4. Using the results in part (a) and (c) determine the;
   1. mass of the glass rod,(2 marks)
   2. density of the glass rod.(2 marks)
5. Remove the glass rod Push the half metre rule through one paper clip and adjust the position of the clip to a point P where the half metre rule balances horizontally. See Figure 1.
   
   Figure 1
6. Record the centimetre mark for point P in Table 1.
7. Repeat part (f) for the other number of clips shown in Table 1 and complete (the clips may be suspended by connecting them as a chain of the required number (4 marks)
                       Table 1
   

   number of clips N	1	2	3	4	5	6
   cm mark of P(cm)
   distance L (from c to p)
   1/L(cm21)

8. Plot a graph of ¹/_L (y axis) against the number of clips N. (4 marks)
   
9. Determine the slope S of the graph.(3 marks)
10. Determine K given that: ¹/_L = 0.05 KN (2 marks)

QUESTION 2
You are provided with the following:

1. A voltmeter 
2. A resistor labelled 1012
3. A resistance wire mounted on a half metre rule labelled X
4. Two cells in a cell holder 
5. A switch 
6. Eight connecting wires 
7. A micrometer screw gauge 
8. A resistor labelled 10KO 
9. A galvanometer 
10. A beaker containing a liquid labelled L 
11. Two copper plates 
12. A resistance wire labelled AB and mounted on a millimetre scale
13. Ajockey 
14. A vernier calliper

Proceed as follows:
PART A 

1. Measure and record the diameter d of the resistance wire x (1 mark)
   d = .............................. mm
      =...............................mm
2. Set up the circuit as shown in Figure 2.
   
   
   1. Close the switch and record the potential difference V₁ across the 100 resistor.
      V₁ = ...............................................(1 mark)
   2. Open the switch. Determine the current I flowing in the circuit. (2 marks)
3.                          
   1. Now connect the voltmeter across wire X. Close the switch and record the potential difference V₂ across wire X. (1 mark)
      V₂ = ...............................................(1 mark)
   2. Determine the resistance R of wire X. (2 marks)
   3. Determine the resistance per metre of wire X. (1 mark)
   4. Determine Q given that Q = πkd² (where d is in metres). (2 marks)
                                                 4
      PART B
4.                    
   1. Using the vernier callipers measure and record the width W of one of the copper plates (1 mark)
      W = ...................cm
   2. Determine the area A of a 5 cm length of the copper plate
      A = ............... cm² (1 mark)
5. Using stands and clamps, hold the copper plates in the beaker such that both plates:
   1. reach the bottom of the beaker,
   2. are parallel, vertical and facing each other,
   3. are separated from each other by a distance S.
6. Connect the copper plates to the circuit as shown in Figure 3.
   
   Figure 3
7. Set the separation distance between the copper plates Sto 3 cm. Using the jockey tap wire AB at various points to obtain a point P at which the galvanometer does not show any deflection. Record the balance length L (from A to P) in Table 2.
8. Repeat part (g) for other values of S shown in Table 2 and complete the table. (6 marks)
              Table 2
   

   Plate separation distance S(cm)	3	4	5
   Balance length L (cm)
   Resistance R = (10 x 103)D                          (100-D)
   Resistance per unit length K = R                                               S
   constant Z = A.K.

9. Determine the average value of Z. (2 marks)

MARKING SCHEME

1.              
   1. V = 3.4 cm³ ± 0.2
   2. C =25.3 cm ± 0.1
   3. X= 2.2 cm ± 0.1
   4.                     
      1. 10 x 2 = mx 2.2
         M = ^m/_v 10 x 2
                        2.2
         = 9.1g  ± 0.1
      2. p = ^m/_v
         = 9.1
            3.4
         =2.68gcm^-3
   5.                                      
   6. Table 1 
      

      number of clips N	1	2	3	4	5	6
      cm mark of P(cm)	45	35.2	32.1	30.2	29.2	28.5
      distance L (from c to p)	19.7	9.9	6.8	4.9	3.9	3.2
      1/L(cm21)	0.05	0.10	0.15	0.20	0.26	0.31

   7.                                        
   8.                                    
      
       
   9.      
   10. 1 = 0.05kN
       L   
       1/L = 0.05k
        N       
       0.05 = k
       0.05 
       k = 1
2.                      
   1. d = 0.36  ± 0.5
      =3.6 x 10^-4m
   2.                          
      1. V₁ = 1.7V ± 0.2
      2. I = V 
              R
         =1.7
           10
         =0.17A
   3.                      
      1. V₂ = 1.0V ± 0.2
      2. R = V 
                l
         =  1  
           0.17
         = 5.88Ω
      3. K = 5.88 x 2 
         = 11.76 Ωm^-1
         or
         5.88 = 11.76Ωm^-1
          0.5
      4. Q = πKd²
                  4
         = π11.76 x (3 x 10^-4)²
                            4
         = 119.7 x 10-⁸
   4.                                 
      1. W = 5.0cm ± 0.10
      2. area = 5 x 5.0
         = 25.00cm²
   5.                                      
   6.                                      
   7.                                       
   8. Table 2
      

      Plate separation distance S(cm)	3	4	5
      Balance length L (cm)	79.5	82.4	86.2
      Resistance R = (10 x 103)D                          (100-D)	38.8	46.8	62.5
      Resistance per unit length K = R                                               S	12.9	11.7	12.5
      constant Z = A.K.	325.73	295.43	315.63

   9. Z average = 325.73 + 295.43 + 315.63
                                          3
      = 312.26