Physics Paper 2 Questions And Answers - KCSE 2020 Past Papers

THE KENYA NATIONAL EXAMINATIONS COUNCIL
Kenya Certificate of Secondary Education
232/2 PHYSICS Paper 2 (THEORY)

Instructions to candidates

1. Write your name and index number in the spaces provided above.
2. Sign and write the date of examination in the spaces provided above.
3. This paper consists of two sections; A and B.
4. Answer all the questions in sections A and B in the spaces provided.
5. All working must be clearly shown in the spaces provided in this booklet.
6. Non-programmable silent electronic calculators may be used.
7. This paper consists of 14 printed pages.
8. Candidates should check the question paper to ascertain that all the pages are printed as indicated and that no questions are missing.
9. Candidates should answer the questions in English.

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

1. State the observation made on the image in a pin hole camera when the distance between the object and the pin hole is reduced. (2 marks)
2. Figure 1 shows a gold leaf electroscope
   
   
   1. Name the part labelled A. (1 mark)
   2. State the function of the part labelled B. (1 mark)
3. State two measurements that should be taken for one to decide whether a lead acid accumulator is due for charging. (2 marks)
4. Explain what happens to the speed of a water wave as it moves from the shallow to the deep end in a ripple tank (2 marks)
5. The critical angle for a ray travelling from glass to air is 42º. Determine the refractive index of the glass (3 marks)
6. Figures 2(a) and 2(b) show two circuit diagrams with identical lamps and identical cells
   
   State with a reason which of the bulbs will be brighter (2 marks)
7. Figure 3 shows an annular ring.
   
   On the diagram, sketch the distribution of the charge on the ring, when the ring is negatively charged. (1 mark)
8. When iron filings are sprinkled onto a bar magnet, it is observed that there are more iron filings at the ends than in the middle. Explain this observation.(2 marks)
9. Draw a diagram to show a p-n junction connected in the reverse bias mode. (2 marks) 
10. A broadcasting station produces radio waves of wavelength 800 m. Determine their frequency (speed of air is 3 x 10⁸ms^-1)(2 marks)
11. Explain how x-rays are produced in the x-ray tube. (2 marks)
12. State the purpose of a fuse in an electrical circuit. (1 mark) 
13. Figure 4 shows circular water waves incident on a plane reflector placed at an angle to the path of the waves.
    
    Complete the diagram to show the reflected waves. (2 marks)

SECTION B( 55 MARKS)

Answer all the questions in this section in the spaces provided.

14.  
    1. State two ways of minimising power losses during the transmission of electric power. (1 mark)
    2. An electric cooker is rated 2.5 kW, 250 V. State the meaning of these values (1 mark)
    3. A consumer has the following appliances in the house:
       • An electric iron rated 1500 W
       • A water heater rated 500 W
       • An electric cooker rated 2500 W
       • Three bulbs each rated 60 W.
         
         The house is fitted with a 12 A fuse. Determine:
         1. whether the consumer can connect all the appliances to the 240 V power supply at the same time; (4 marks)
         2. the resistance of the heating element used in the electric cooker. (3 marks) 
15.  
    1. Describe how the focal length of a concave mirror can be determined using a screen and a metre rule.(1 mark)
    2. An object is placed 8cm from a concave mirror whose radius of curvature is 20cm.
       Determine the position of the image.(3marks)
    3. An object of height 10 cm is placed 30 cm from a converging lens of focal length 18 cm.
       1. On the grid provided. draw a ray diagram to locate the position of the image formed.(3 marks)
       2. From the diagram in part (i), determine the:
          1. image height; (2 marks)
          2. image distance. (2 marks)
16.  
    1. State two uses of radioactivity in medicine. (1 mark)
    2. The following is a nuclear reaction equation: ⁶₃Li+¹₀n →³₁H +^x_yP
       Determine the values of x and y. (2 marks) 
    3. Figure 5 shows a radioactive element placed in an evacuated glass chamber. The element produces alpha, beta and gamma emissions.
       
       The three emissions pass through an electric field.
       1. Complete the diagram to show the path of each of the emissions. (3 marks)
       2. State the reason why:
          1. the radioactive element is kept inside a lead box: (1mark )
          2. the chamber is evacuated. (1 mark)
    4.  
       1. Arrange the following electromagnetic waves in the order of decreasing frequency:
          Microwaves; Gamma rays; Radiowaves; X-rays. (1 mark)
       2. The half life of a certain radioactive substance is 24 days. Given that the initial (i) sample of the substance has a mass of 64 g, determine the mass which is left after 72 days. (2 marks)
17.  
    1.  
       1. Name the three components of the electron gun in a cathode ray tube.(3 marks)
       2. State one difference between the deflection systems of a cathode ray tube and the television tube. (1 mark)
    2. Figure 6 shows a graph of stopping potential against the frequency for a certain photo emissive surface, drawn by a student from the data collected when carrying out an experiment on photoelectric effect.
       
       From the graph, determine the:
       1. threshold frequency of the surface: (3 marks)
       2. plank's constant h, given that the energy of the incident photon is
          1.6X 10^-19 J; (3 marks)
       3. work function of the surface. (3 marks))
18.  
    1. Figure 7 shows a soft iron ring placed between the poles of two bar magnets. 
       
       On the figure, draw the magnetic field lines between the poles. (2 marks)
    2. Figure 8 shows two straight conductors P and Q connected to a battery and a variable resistor.
       
       1. Using arrows, indicate on the diagram the direction of current that flows through P and Q when the switch is closed. (1 mark)
       2. State what is observed as the current flows through the conductors. (1 mark) 
       3. Explain the observation in (ii). (3 marks)
    3.  
       1. State how eddy currents are minimised in a transformer.(1 mark)
       2. A step down transformer has 600 turns in the primary coil. The input voltage is 120 V while the output voltage is 24 V. Determine the number of turns in the secondary coil.(3 marks)

MARKING SCHEME
(CONFIDENTIAL)

SECTION A: (25 marks) 

1. The image size increases/ becomes larger/ bigger/ magnified
2.  
   1. Gold leaf / leaf 
   2. Protect the surrounding of the metal rod and leaf from damage or draughts /external effects
      external effects. The e.m.f. across it's terminals /
3.  
   • The emf across it's terminals/Voltage/ pod across
   • The relative density of the electrolyte/ density of acid/electrolyte( not liquid)
4. the speed increases since the wavelength λ increases but the frequency is same because source is the same
   ( no mark for contradiction)
5.  π=    1    
          sin c
    =    1    
       sin 42º
   =  1    
      0.669
   = 1.495( accept 2 dp - 1.49/ 1.50/ 1.494)
6.  B
   The two cells series provide a higher electromagnetic force/ potential difference/ current/ voltage 
7.   
      or   
   ( uniformly distributed and must be on the surface)
8. There is a greater magnetic force at the ends due to increased field lines at the ends of the bar magnet than at the centre of the bar magnet./ high flux density/ or due to higher concentration of field lines at the ends.
9.    
   
   ( reject incomplete circuit)
10.  f = 3 x 10⁸ 
              λ
         3 x 10⁸  
           800
    = 0.00375 x 10⁸ Hz
    = 3.75 x 10⁵ Hz
11.   
    • Electrons are produced by thermionic emission
    • Electrons are accelerated by high voltage
    • Electrons are suddenly stopped to produce x-rays/ stopped by hard surface
      (marks not tied. They are independent)
12.  To disconnect circuit when excess current flows( break)/ protect/ guard appliances from excess current/ electrical fire
13.    
    
    √ curve correctly
    √ angle of reflection
    ( check for correct shapes)
    ( correct wavelength and angles)
14.    
    1.   
       • Stepping up the voltage/ current
       • Use of good conductor cables/ thick cables
    2.   The electric cooker has power output of 2500W when it operates at a potential of 250v, P=V1
    3.  
       1. Total power = 1500 + 2500 + 500 +( 60x3)
          = 4680 W
          Total current required = 4680 = 19.5A
                                               240
          Hence fuse blows and disconnects the current when it exceeds 10A ie, all appliances can't be connected at the same time/ max current for all appliances connected is higher than the fuse rating.
       2. I =  P   = 2500
                v         240
          R= 240 ÷ ( 2500/ 240)
          = 240 x 240
                 2500
          = 23.04Ω
15.   
    1.   
       • Using the mirror focus a distant object on to the screen
       • Adjust the distance the screen & mirror to obtain a sharp image
       • Measure the distance between the screen & the mirror - this is the focal length of the mirror
         ( using the metre rule measure the distance between the screen and the mirror)
    2.  1 = 1 + 1 
        f     u     v
        1  =  1  -  1  
        v     10     8
        1 = 4-5   
        v     40
       v= 40cm
    3.  
       1.  For diagram, check:
           Correct scale
          correct rays
          Correct image post
          Correct tilt
          
          
          
       2.    
          1. Image height = 15cm
          2. Image distance = 45cm
16.   
    1.   
       • Sterilization of medical equipment
       • Treatment of malignant growths/ radio therapy/ killing cancerous cells / removing thyroid glands
    2.  x = 4
        y= 2
    3.   
       1. 
          
          
          • Don't award when passing through the plate
          • Deflected earlier and moves further
          • Deflected later and doesn't move further
       2.    
          1. To shield the radiation from moving to the other direction
          2. Prevent collision of clear vision on the effect of the field/ minimise loss of / prevent ionisation
    4.    
       1. Gamma rays, X- rays, microwaves , radio waves
       2. 64      →    32    →     16      →       8
              24 days      48days      72 days  
          3 half lives, 8g left
          alternatively, 
          64 x (1/2)³ 
17.    
    1.   
       1.   
          • The heating coil/ cathode
          • Grid
          • The anodes
       2. The cathode ray tube uses plates for deflection while a television tube uses coils
          ( CRT - electric fields while TV uses magnetic field)
    2.   
       1. eVs = hf - hfo
          at Vs = 0
          hf = hfo
          f = fo which is obtained by extrapolating the graph to obtain the √ value of fo when Vs=0
          
          4.6 x 10¹⁴ 1 +2 ± 0.1
          Second mark check is student has used graph ( extrapolates/ put a mark)
          
          
          
       2.  Vs =  hf  -  hfo 
                    e       e
            h (f-fo)
            e
            h  = gradient
            e
          =   1.25 - 0.5  
              (8-6) x 10¹⁴ 
          = 0.75 x 10^-14  
                2
          = 0.375 x 10^-14 
          h= 3.75 x 10^-15 x 1.6 x 10^-19 
          6.0 x 10^-34 Js ± (0.8)
          alternatively, 
          E= hf
          h=E/f
           = 1.6 x 10^-19  
                   f
          Read from graph = ans
          f = ( 4.6 x 10¹⁴ - 10 x 10¹⁴)
          Range ( 1.6 x 10^-34 - 3.478 x 10^-34) Js
       3. Wo = hfo
          = 6.0x10^-34x4.36x10¹⁴
          =2.76x10^-19J
18.   
    1.    
       
       ( 2 fields, direction - independent)
    2.   
       1. 
          
          on the diagram
       2. The two conductors repel/ move away/ distance below conductors increases
       3. As the current flows, a magnetic field develops around each conductor such that the field between the conductor reinforce each other creating a stronger force.
    3.   
       1.  By laminating the core
       2.  N1 =  Vs 
           N_p     V_p 
            N₁ =  24 
          600     120
          N₁ = 120 turns