KCSE 2014 Physics Paper 2 Questions with Marking Scheme

QUESTIONS

SECTION A (25 marks)
Answer all the questions in this section in the spaces provided.

1. Figure 1 shows two parallel rays from a distant object passing through a convex lens:
   
   
   
   
   1. Indicate on the diagram, the position of the principal focus on the lens. (1 mark)
      
      
   2. Deremine the focal length of the lens. (1 mark)
      
      
2. State the effect of decreasing the distance between the plates of the parallel plate capacitor on the capacitance. (1 mark)
   
   
3. Figure 2 shows circular waves originating from the principal focus F of a concave mirror and moving towards the mirror.
   
   
   
   Complete the diagram to show the refflected waves. (1 mark)
   
   
4. The force of an electromagnetic wave is 4.0 x 10⁶ Hz. Determine its wavelength. (take speed of light as 3.0 x 10⁸ ms^-1) (3 marks)
   
   
5. Figure 3 shows a nail on which a wire is to be wound to make an electromagnet.
   
   
   
   By drawing, show how the wire should be wound around the nail so that end A becomes a north pole and B becones a south pole. (1 mark)
   
   
6. It is observed that when the cap of an uncharged electroscope is irradiated with light of high frequency, the leaf of the electroscope rises. Explain this observation. (3 marks)
   
   
7. Figure 4 shows the magnetic field pattern around two bar magnets placed side by side.
   
   
   
   Indicate on the diagram the poles of each magnet. (1 mark)
   
   
8. Figure 5 shows a graph ofcurrent against voltage for a semiconductor diode.
   
   
   
   In the space provided, draw a circuit diagram that may be used to obtain values needed to draw the graph in figure 5. (3 marks)
   
   
9. Radium undergoes radioactive decay by emiting an alpha particle to form a daughter nuclide Q as in the reaction:
   
   
   
   Determine the values of:
   1. x (1 mark)
   2. y (1 mark)
      
      
10. State two uses of a charged gold leaf electroscope. (2 marks)
    
    
11. The anode of an x-ray tube becomes hot when the tube is in use. State the reason for this. (1 mark)
    
    
12. Draw a ray diagram to show how a ray of light may be totally internally reflected two timesin an isosceles right anlgled glass prism. (Assume that the critical angle of glass is 42⁰) (2 marks)
    
    
13. The current of electrons hitting the screen of a cathode ray oscilloscope is 2.0 x 10^-4 A.
    Determine the number of electrons that strike the screen each second. (take charge of an electron as 1.6 x 10^-19 C)
    
    
                                                  SECTION B (55 marks)
                        Answer all the questions in this section in the spaces provided.
    
14. 1. Figure 6 shows a simple electric bell circuit.
       
       
       
       
       1. Name the parts labelled:
          1. D (1 mark)
          2. E (1 mark)
       2. When the switch is closed, the hammer hits the gong repeatedly. Explain why:
          1. The hammer hits the gong. (2 marks)
          2. The hammer hits the gong repeatedly. (3 marks)
             
             
    2. An electric bulb is rated 60 W, 240 V. Determine:
       1. the current that flows through it when it connected to 240 V supply. (3 marks)
       2. the resistance of the bulb. (3 marks)
          
          
15. 1. One of the causes of energy loss in a transformer is heating in the coils when current flows. State:
       1. The reason why the current causes heating. (1 mark)
       2. How the heating can be minimized. (1 mark)
          
          
    2. The input voltage of a transformer is 240 V and its output is 12 V. When an 80 W bulb is connected across the secondary coil, the current in the primary coil is 0.36 A.
       Determine:
       1. The ratio N_p/N_s of the transformer, (where Np is the number of turns in the primary coil and Ns is the number of turns in the secondary coil) (3 marks)
       2. The power input of the transformer. (3 marks)
       3. The power output of the transformer. (1 mark)
       4. The efficiency of the transformer. (2 marks)
          
          
16. 1. Figure 7 shows resistors R₁ and R₂ connected in parallel. Their ends are connected to a battery of potential difference V volts.
       
       
       
       
       1. In terms of V₁,R₁ and R₂, write an expression for:
          1. Current I₁ through R₁. (1 mark)
          2. Current I₂ through R₂ . (1 mark)
          3. Total current I in the circuit. (1 mark)
       2. Show that the total resistance R_T is given by  (3 marks)
          
          
    2. Figure 8 shows a negatively charged rod placed near an uncharged conductor resting on an insulating support.
       
       
       
       
       1. Show the charge distribution on the conductor. (2 marks)
       2. State the effect:
          1. Of momentarily touching the conductor with a finger while the charged rod is still near the conductor. (1 mark)
          2. On the charge distribution of withdrawing the negatively charged rod after momentarily touching the conductor. (1 mark)
             
             
       3. In the space provided, sketch a diagram to show how the charge in (ii) (II) above would have been distributed if the conductor was a sphere. (1 mark)
          
          
17. 1. Figure 9 shows two speakers S₁ and S₂ which produce sound of the same frequency. They are placed equidistant from a line AB and a line PQ. (PQ is perpendicular to line AB)
       
       
       
       
       1. A student walking from A to B hears alternating loud and soft sounds. Explain why at some point the sound heard is soft. (2 marks)
       2. The student now walks along line PQ. State the reason the nature of the sound the student hears. (3 marks)
          
          
    2. Figure 10 shows sound waves in air produced by a vibrating tuning fork. R is an air molecule on the path of the waves.
       
       
       
       
       1. Using a line, indicate on the diagram a distance d equal to the wavelength of the wave. (1 mark)
       2. In the space provided, show with an arrow the direction of motion of the air molecule fr as the waves pass. (1 mark)
       3. Explain the reason for the answer in (ii). (2 marks)
          
          
18. Figure 11 shows an object placed 10cm infront of a concave mirror whose radius is of curvature is 40 cm.
    
    
    
    
    1. 1. On the same figure, draw a diagram to show the position of the image formed. (3 marks)
          
          
       2. Use the ray diagram to determine:
          1. the image distance. (1 mark)
          2. the magnification. (3 marks)
             
             
       3. State where the position of the image would be if the object had been placed at the principal focus. (1 mark)
          
          
    2. Draw a ray diagram to show the formation of a partially dark shadow and a totally dark shadow during the eclipse of the sun. (3 marks)

MARKING SCHEME

1.                        
   1.                
      
   2. Focal length = 10 cm. √1
2. The capacitance increases. (1 mark)
3. Approximately equally spaced lines √ 1
   
4.                  
   1.  V  = fλ
      λ = 3.0 × 10⁸
             4 × 10⁶
      75 m√ 1
5.                                      
    correct winding
6.                    
   1. Electrons arbsorb enough energy and are ejected√ leaving the electroscope positively charged √ the leaf is repelled by the stem. √
7.                              
   
8.                                        
   
   OR equivalent
   1 mark for correct bias
   1 mark for both ammeter and voltmeter
   1 mark for means of varying the p.d. across the diode.
9.          
   
   
   1. 4 + x =226
      x = 222√ 1
   2. 2 + y =88
      y = 86√ 1
10. -estimate the quantity of charge √1
    - test for insulating properties √1
    - test for the sign of charge √1
    - test for presence of charge √1
    (any two correct)
11. It stops the fast moving electrons √ whose kinetic energy is converted to heat.
12.                       
    
    1 mark for ray incident on hypotenuse
    1 mark for showing two internak reflections
13.                        
    1 mark for either formula
    = 2.0 × 10^-4 × 1      1 mark for substitution
          1.6 × 10^-19  
    = 1.25 × 10¹⁵ electrons       1 mark for answer
14.                          
    1.                      
       1.                          
          1.  D - soft iron armature √ 1
          2. E - contacts √ 1
       2.                    
          1. Soft iron core is magnetised √ and 1 attracts the armature √ the hammer hits 1 the gong.
          2. Contact is broken √ when armature is 1 attracted by the core. The core then loses magnetism. √ 1 The armature loses magnetism and √ springs back making contact again and the process is repeated.
    2.                        
       1. I = P
               V
          = 60 
            240
          = 0.25A √ 1
       2. R  = V 
                  I
          R = 240 × 240 = √ OR  240
                      60                   0.25
           = 960 Ω
15.          
    1.                                                
       1. resistance in the coils. √ 1 
       2. use of thicker copper wires. √ 1
    2.                                  
       1. N_P = V_P
          N_S   V_S
          =240
             12
          =20
             1
       2. Power input = 80W
       3. Efficiency = power output
                            power input
          = 80
            86.4
          = 92.59% √ 1
16.                           
    1.                      
       1.               
          1. I₁ = V
                    R₁
          2. I₂ = V
                   R₂
          3. I_r = I₁ + I₂
             I_T = V + V
                    R₁   R₂
       2.  I_T = V
                  R_T
          V = V  +   V
          R_T   R₁       R₂
          divide through by V
          1 = 1 + 1 HENCE R_T =R₁R₂
          R_T   R₁   R₂                    R₁ + R₂
    2.                   
       1.                    
          
          -concentration of positive charges at sharp end
          +ve & -ve charges in correct position
       2.                  
          1. The conductor loses the negative charges to earth. √ 1
          2. The conductor acquires a net √ positive charge/which redistributes itself.
       3.                      
          
          +ve charges uniformly distributed
17.                          
    1.                      
       1.                        
          1. sound is soft when the waves arrive out of phase; √ 1 such waves undergo destructive interference. 1
          2. same sound - loud. √ 1
             Along PQ the waves undergo 1 constructive intereference as they arrive in phase. √ 1
    2.                  
       1.                
          
          any correct d
       2.                                                    
          
       3. As the longitudinal waves pass √ molecule R moves along to either side. 1 For a crest, R moves away from source.
18.                                  
    1.                              
       
    2.                            
       1. image distance = 20 cm ± 2 cm √ 1
       2.  magnification = image distance
                                  object distance
          =20
            10
          = 2 ± 0.2 √ 1
       3. Infinity. √ 1
          
          - Outer pair of rays √
          - Inner pair of rays √
          - proper labelling of umbra and penumbra √