PHYSICS PAPER 2 - KCSE 2019 ALLIANCE MOCK EXAMINATION

SECTION A: 25marks

1. The chart below shows an arrangement of different parts of the electromagnetic spectrum.
   

   Radio wave

   A

   Infrared rays

   B

   Ultra-violet

   c-Rays

   
   
   1. Name the radiation represented by
      A                                                        (1mark)
   2. State one use of radiation represented by B                                                                               (1mark)

2. An object O is placed in front of convex mirror as shown in the diagram below. Complete the diagram to locate the position of the image, 1.  (3 marks)
   

3. The figure below shows a wire carrying current whose direction is out of the paper.   The wire is placed in a magnetic field.
   
   
   1. Indicate on the figure the direction of the force F, acting on the wire.                                   (1 mark)                                          
   2. State what would be observed on the wire if the direction of the current is reversed.            (1 mark)

4. The figure below shows part of the lighting circuit of a house. 
   
   
   1. Give a reason why a fuse is included in the circuit.                                                               (1 mark)
   2. If each lamp has a power of 60W at voltage of 240V. Calculate the current through one lamp when it is switched on.       (2 marks)
5. Figure 5 below shows a simple transformer connected to a 12v a.c source and an a.c voltmeter.
   
   Determine the reading on the voltmeter.   (2 marks)                                                                                            

6. The diagram shows a patient having her eyes tested. A chart with letters on it is placed behind her and she sees the chart reflected in a plane mirror.
   
   Determine how far away from the patient, the image of the chart is seen.                                (2 marks)                                         

7. State Snell’s law.     (1 mark)                                                                                                
8. The figure below shows an electric circuit.
   
   State and explain how the potential difference across X varies as the light shining on it becomes brighter.         (2marks)  

9. Waves pass from deep water to shallow water and refraction occurs.
   
   Calculate the speed of the waves in the shallow water   (2 marks)                                                                   

10. The diagram below shows a ray of light striking the plane at 35^o as shown below.
    
    State the angle of reflection.          (1 mark)

11. The figure below shows an iron bar being magnetized by stroking it with a magnet.         
                  
    Indicate on the iron bar the polarity of resulting magnet.               (1 mark)

12. An echo sounder of a ship transmits sound waves to the depth of the sea and receives the echo after 2.4 seconds. If the speed of sound in water is 1600ms^-1, determine the depth of the sea.  (3 marks)
13. It is observed that when a charged body is brought near the cup of a positively charged electroscope, the divergence of the leaf increases. State the type of charge on the body.       (1mark)                                          

SECTION B (55 marks)

14.  
    1. The figure below shows a diagram of a Geiger Muller tube connected to a power supply and a pulse counter.
       
       
       1. Why should the argon gas be at low pressure?   (1mark)
       2. State the purpose of the bromine gas in the tube.    (1mark)
       3. Suggest one way of increasing the sensitivity of the tube   (1mark)
       4. Find the value of a and b in the following equation.    (2marks)
          
    2. The figure below shows a PN junction diode used in a rectifier.
       
       
       1. What is an extrinsic semi conductor? (1mark)
       2. What type of rectification is shown?                        (1mark)
       3. Describe how the rectification is achieved                                                                        (2marks)
       4. In the space provided below, sketch the output signal displayed on the CRO during the rectification process.       (2marks) 
          

15.  The figure below shows a cathode ray tube   
                                                          
    1. State the function of the
       1. Heater                                                                                                                     (1mark)
       2. Extra High Tension (E.H.T.)                                                                                (1 mark)
    2. State how the intensity of the fluorescence on the screen can be increased.       (1 mark)
    3. State the effect of having air in the tube instead of a vacuum (1 mark)
    4. State one properties of cathode rays (1 mark)
    5. Distinguish cathode rays and X-rays                                                                   (1 mark)
    6. Give one advantages of using a C.R.O instead of a voltmeter in measuring voltages            (1 mark)
    7. The figure below shows an a.c. voltage. If the Y-gain control reads 10V/cm and the time base reads 5 milliseconds/cm
       
       Calculate:
       1. The frequency of the alternating voltage (2 marks)
       2. Peak to peak voltage of the alternating voltage                                                  (2 marks)
16.  
    1.  
       1. It is observed that when ultra- violet radiation is directed onto a clean zinc plate connected to the cap of a negatively charged leaf electroscope, the leaf falls .Explain this observation      ( 2 marks)
       2. State why this observation does not occur if the electroscope is positively charged           (1 mark)
       3. Explain why the leaf of the electroscope does not fall when infra- red radiation is directed onto the zinc plate     ( 1 mark)
    2. State the effect on the electrons emitted by the photoelectric effect when:
       1. The intensity of incident radiation is increased                                             (1 mark)
       2. The frequency of the incident radiation is increased                                     (1 mark)
    3. Light of wavelength 4.3 x 10^-7m is incident on two different metal surfaces, nickel and potassium. (Take speed of light as 3.0 x 10⁸ ms^-1 and planks constant h as(6.63 x l0^-34Js).
       1. Determine the energy of the incident radiation.                                          (3 marks)
       2. If the work function of nickel is 8.0 x 10^-19J and that of potassium is 3.68 x 10^-19J, state with a reason from which of the two metals the given light will eject electrons.(2 marks)
       3. Determine the velocity of the emitted electrons from the metal surface in b(ii).
          (Take the mass of an electron as 9.1 x 10^-31 kg).                                            (2 marks)
17.  
    1. The figure below shows three resistors as shown. 
       
       If the voltmeter reads 4V, find the
       
       1. Effective resistance                                                                                               (3marks)
       2. Current through the 3W resistor                                                                           (2 marks)
       3. Potential difference across the 8W resistor if the voltage total voltage in the circuit is 10V                                                                                                                         (1 mark)
    2.  
       1. What is meant by the term “terminal voltage” as used in current elecricity?
       2. A cell supplies a current of 2.0A when connected to a 0.6W resistor and 1.5A when the same cell is connected to a 0.9WFind the e.m.f and the internal resistance of the cell. (3marks)
18.  
    1. Give a reason why a candle flame is blown when a highly charged conductor is brought close to it as shown below.     (1mark) 
       
    2. State two factors that affect capacitance of a capacitor                      (2 marks)
    3. The figure below shows 1μF, 2μF, 4μF and 5μF capacitors connected to a battery. 
       
       Determine:
       1. The total capacitance. (3marks)
       2. The total energy stored by the capacitors.         (2marks)
       3. Voltage across the 4μF capacitor.          (2marks)

MARKING SCHEME

1. A -  microwave
   B - for vision
2.  
   

3.  
   1.  
      
   2. moves on the opposite side.
4.  
   1. safeguard appliances from excessive current
   2. P=VI
      60=240 I
      I=0.25A

5. Ns/Np=Vs/Vp
   5/10=Vs/12
   Vs=6V

6. 3m+2m=5m

7. the ratio of sine of angle of  incidence to sine of angle of refaction is the same for a pair of media.

8. Pd reduces,resistance reduces.

9. f =V/ λ                       
   V₁/λ₁=V₂λ₂
   2/1=V₂/0.4
    V₂=0.8m/s

10. 90-35=55^o
11.  
    

12. d=1/2st
    1/2x1600x2.4=1920m

13. negative charges

14.  
    1.  
       1. Argon – to initiate the discharge.
       2. Quenching agent.       
          Absorb energy of positive ions before they cause secondary electron emission.
       4. a = 226  b=88
    2.  
       1. semiconductor that has been added impurities to enhance electrical conductivity
       2. half wave rectification
       3. During the first cycle (positive) the diode is forward biased, so it conducts, so current flows through the resistance 
          During the second cycle (negative) the diode is reverse biased so it does not conduct, the process repeats itself. 
                                

15.  
    1.  
       1. to provide heat by thermiomic emission
       2. to create high pd for the anode
    2. increasing the pd of the grid and cathode
    3. cause ionization
    4. posses kinetic energy travel in strait lines
    5. x-rays-formed due  to changes in electron structure while gamma rays-formed from changes  nucleus  structure of an atom
    6. can measure both ac and dc voltages
       can measure larger voltages
    7.  
       1. T=5x4=20ms
          f=1/T=1/0.02
          f=50Hz
       2. V=10x4=40V

16.  
    1.  
       1. electron emitted are repelled  by the negative charges, so the leaf of electroscope fall
       2. electron emitted area attracted by the positive charged
       3. its energy is lower than the energy need to dislodge an electron from a metal surface
    2.  
       1. increase in the rate of emission of electrons
       2. speed of electrons increases
    3.  
       1. E=hf
          (6.63x10^-34x3.0x10⁸)/(4.3x10^-7)
          =4.6256x10^-19J
       2. potassium, lower  work function an also less energy than energy of radiation
       3. E = 1/2mv²
          V²= (2x 0.9456x10^-19)/(9.1X10^-31)
          V=4.559X10⁵m/s

17.  
    1.  
       1. R_P=(R₁R₂)/(R₁+R₂)
          R_S=(R₁+R₂)
          (3X6)/(3+6)+8
          10Ω
       2. V=IR
          I  = 4/3
          = 1.333A
       3. 10-4 =6V
    2.  
       1. pd across a cell when it is supplying current
       2. E = IR+Ir
          E = (2X0.6)+2r          
          E=1.8V,r = 0.3Ω 
          E = (1.5+0.9)+1.5r                                            

18.  
    1. ionization occurs, positive charges drift away    / This due to an electric wind set up by the high concentration of charge at the sharp point. Air is ionized and like charges repel.
    2. area of overlap
       distance of seperation                                                                                                                                                                                                                                                                                                                                                                                        
    3.  
       1. 1μF +4μF = 5μF
          Series = (5x5)/10 = 2.5μF;
          Total capacitance = 2.5 +2 = 4.5 μF
       2. Energy =1/2cv²
          =1/2x4.5x10^-6x8²
          =1.44x10^-4 J
       3. Total charge = 4.5 x 8 =36μC, Voltage =  4v