Physics Paper 2 Questions and Answers - Moi Kabarak High School Mock 2020/2021

INSTRUCTIONS TO STUDENTS

• Answer ALL the questions in the spaces provided.
• All working MUST be clearly shown.
• Mathematical table and electronic calculators may be used.
• Answers should be in decimal points and NOT fractions.

SECTION A (50 MARKS)

1. The figure below shows an object placed in front of a plane mirror.
   
   Sketch the image of the object as seen in the mirror.  (1 mark)
2. The neutral identical aluminium spheres A and B are hanged freely such that they are in contact, as shown in the figure. A negatively charged rod is brought close to the spheres as shown.
   
   One of the spheres B is earthed momentarily by touching with finger and then the rod is withdrawn. State and explain the observation made.  (2 marks)
3. The circuit below shows a torch bulb and lead plates dipped in dilute sulphuric acid and a battery of emf 12V.
            
   
   1. What would be observed if switch S₁ is closed and S₂ open? Give a reason for your answer.   (2 marks)
   2. State what is observed when S₁ is open and S₂ closed.    (1 mark)
   3. S₂ was closed for sometime and then opened and S₁ closed. State what was observed.    (1 mark)
4. Complete the ray diagram below, to show how a convex lens works as a magnifying glass.   (3 marks)
   
5. A convex lens forms an image three times the size of the object on a screen. If the distance between the screen and the object is 120cm. Determine;
   
   1. The object distance.      (2 marks)
   2. The focal length of the lens.      (2 marks)
6. State the function of ammonium chloride paste in a dry cell.     (1 mark)
7. Describe briefly how an N-type and a P-type semi conductors are made. (2 marks)
8. An immersion heater rated 4000W is used continuously for 1hour 30 minutes. Calculate the cost of operation at Ksh.6.70 per unit.    (2 marks)
9. State one advantage of the circuit breaker over a wire fuse.    (1 mark)
10. The figure below shows the displacement-time graph of a certain wave.
    
    Determine the frequency of the wave.    (2 marks)
11. The figure below shows an electric circuit connected to a battery. If the internal resistance of the battery is 0.2Ω.
    
    Determine the electromotive force e.m.f of the battery.      (3 marks)

SECTION B: (55 MARKS)

12.  
    1. Given a large source of light screen and a large object, sketch a ray diagram to show the shadow formed on the screen.   (3 marks)
    2. Explain why a plain sheet of paper and a plane mirror both reflect light yet only the plane mirror forms images while the paper cannot form images.       (2 marks)
    3. The diagram below shows the path of light after striking two mirrors at an angle
       
       Determine the angle between the mirrors.      (2 marks)
    4. The figure below shows a convex mirror.
       
       Show on the same diagram how the convex mirror provides to the eye looking into it,a wide field of view.          (2 marks)
13. A student designed a transformer to provide current to an electric bell marked 24W,6V from mains supply of 240V. He wound coils 50 turns and N turns on an iron ring. When he connected the coil of 50 turns to the bell and N turns to the a.c source he found out that the transformer was only 60% efficient. Find;
    1. The value of N     (2 marks)
    2. The power in the primary coil.   (2 marks)
    3. State two ways in which the efficiency of the transformer can be increased.     (2 marks)
    4. State and explain two factors that determine the magnitude of induced emf in a coil rotating in a magnetic field.
       (2 marks)
14.  
    1. State two factors that determine the speed of electrons emitted from a metal surface by light energy falling on it. (2 marks)
    2. The figure below shows the apparatus used to investigate photoelectric effect of a certain radiation.
       name the labelled parts A, B and C.      (3 marks)
       
    3. A photosensitive cathode of work function 2.1ev is irradiated by a radiation of wave length, 4.5 x 10^-7m(Take C = 3.0 x 10⁸ms⁻¹, h = 6.63 x 10^-34JS and 1ev = 1.6 x 10^-19J.)
       Determine:
       The stopping potential on the cathode. (e = 1.6 x 10^-19C)        (3 marks)
    4. The graph below shows the stopping potential against frequency of the incident radiation of different colours of light on a photocell.
       
       From the graph determine the threshold wave length.    (2 marks)
15.  
    1. State two factors that affect the capacitance of a parallel plate capacitor.    (2 marks)
    2. The figure below shows an arrangement of capacitors connected to 12.0V d.c. supply.
       
       Determine;
       1. The effective capacitance.   (3 marks)
       2. The total charge in the capacitors.     (2 marks)
       3. The charge store in the 3μF capacitor.    (2 marks)
16. The figure below shows a waveform on a CRO screen,
    
    Given that the y-gain control is set to 20V/cm and the time base set at 10ms/cm.
    Calculate;
    
    1. The peak voltage fed onto the y-plates.     (2 marks)
    2. The periodic time of the wave.     (2 marks)
    3. The frequency of the wave form.         (2 marks)
    4. Explain what is meant by thermionic emission        (1 mark)
    5. State two advantages of a CRO over conventional voltmeter.  (2 marks)
17. The figure below shows the common features of an x-ray tube.
             
    
    1. Name the parts labelled A and B.
       A -     (1 mark)
       B -       (1 mark)
    2. What property of lead makes it suitable for use as shielding material?    (1 mark)
    3. Explain how the intensity of the x-rays from such a tube may be increased.      (1 mark)
    4. If the x-ray tube is operated with an anode voltage of 10KV and a tube current of 160MA,
       Given
       • Charge of an electron = 1.6 x 10^-19C
       • Mass of an electron = 9.1 × 10^-31 kg.
         Planck's constant = 6.63 x 10^-34JS
         1ev = 1.6 x 10^-19J.
         Determine the velocity of an electron striking the target.     (4 marks)
18.  
    1. The figure below shows the path of a radiation from a radioactive source moving in a magnetic field perpendicular
       
       Identify the radiation.    (1 mark)
    2. Below is a nuclear equation for a fission process resulting from reaction on a neutron with a uranium nucleus.
       
       Determine the values of X and Y.
       X         (1 mark)
       Y         (1 mark) 
    3. Define the term half-life as used in radioactivity.   (1 mark)

Marking scheme

SECTION A (50 MARKS)

1. The figure below shows an object placed infront of a plane mirror.
   
   Sketch the image of the object as seen in the mirror.  (1 mark)
2. The neutral identical aluminium spheres A and B are hanged freely such that they are in contact, as shown in the figure. A negatively charged rod is brought close to the spheres as shown.
   
   One of the spheres B is earthed momentarily by touching with finger and then the rod is withdrawn. State and explain the observation made.  (2 marks)
   • The spheres will repel
   • Both are charged positively by induction
3. The circuit below shows a torch bulb and lead plates dipped in dilute sulphuric acid and a battery of emf 12V.
            
   
   1. What would be observed if switch S₁ is closed and S₂ open? Give a reason for your answer.   (2 marks)
      • No observable change- Bulb does not light
      • No current flows from the lead plates as not charged
   2. State what is observed when S₁ is open and S₂ closed.    (1 mark)
      • Gas bubbles observed on the two plates.
      • positive plate turns dark brown 
      • charging takes place.
   3. S₂ was closed for sometime and then opened and S₁ closed. State what was observed.    (1 mark)
      • The bulb lights - The plates have been charged
4. Complete the ray diagram below, to show how a convex lens works as a magnifying glass.   (3 marks)
   
5. A convex lens forms an image three times the size of the object on a screen. If the distance between the screen and the object is 120cm. Determine;
   
   1. The object distance.      (2 marks)
      ^v/_μ=3
        v=3μ
      μ+ v =120cm
      μ+3μ=120cm
          4μ=30cm   
   2. The focal length of the lens.      (2 marks)
      f= μv  =  3μ²ⁱ = 3 × 30 × 30  =22.5cm
         μ+v    μ+v            120
6. State the function of ammonium chloride paste in a dry cell.     (1 mark)
   • It is an electrolyte.
7. Describe briefly how an N-type and a P-type semi conductors are made. (2 marks)
   • N-type. Doping an intrinsic semiconductor with pentavalent atoms
   • P-type. Doping an intrinsic semiconductor with trivalent atoms
8. An immersion heater rated 4000W is used continuously for 1hour 30 minutes. Calculate the cost of operation at Ksh.6.70 per unit.    (2 marks)
   4000w=4Kw × 1.5hrs × 6.70
             =ksh.40.20
9. State one advantage of the circuit breaker over a wire fuse.    (1 mark)
   • Can be closed by mechanical means once the problem causing excessive current has been corrected or can be reset for use.
10. The figure below shows the displacement-time graph of a certain wave.
    
    Determine the frequency of the wave.    (2 marks)
    T=4 × 10⁻³s
    f =  1   =        1           =250HZ
          T       4×10⁻³s e
11. The figure below shows an electric circuit connected to a battery. If the internal resistance of the battery is 0.2Ω.
    
    Determine the electromotive force e.m.f of the battery.      (3 marks)
    Effective resistance
    =(10 × 5) +2Ω +0.2Ω
       (10+5)
    =5.533Ω
    I in 10Ω=^10v/_10Ω =1.0AM
    Total current
    =(2.0 +1.0)A =3.0A
    E=3.0A × 5.533Ω
      =16.6V

SECTION B: (55 MARKS)

12.  
    1. Given a large source of light screen and a large object, sketch a ray diagram to show the shadow formed on the screen.   (3 marks)
       
    2. Explain why a plain sheet of paper and a plane mirror both reflect light yet only the plane mirror forms images while the paper cannot form images.       (2 marks)
       • Plane mirrors form images by regular reflection while paper will produce irregular reflection.
    3. The diagram below shows the path of light after striking two mirrors at an angle
       
       Determine the angle between the mirrors.      (2 marks)
       
       • 70°
    4. The figure below shows a convex mirror.
       Show on the same diagram how the convex mirror provides to the eye looking into it,a wide field of view. 
       (2 marks)
       
13. A student designed a transformer to provide current to an electric bell marked 24W,6V from mains supply of 240V. He wound coils 50 turns and N.. turns on an iron ring. When he connected the coil of 50 turns to the bell and N turns to the a.c source he found out that the transformer was only 60% efficient. Find;
    1. The value of N     (2 marks)
       ⁵⁰/_N =⁶/₂₄₀
          6N=12000
           N=2000turns
    2. The power in the primary coil.   (2 marks)
       60% → 24W
       100%   =(¹⁰⁰/₆₀ × 24) = 40W
    3. State two ways in which the efficiency of the transformer can be increased.     (2 marks)
       • Using a core of soft magnetic material
       • Winding primary and secondary coil on the same soft iron core
       • using thick copper wires to make the coil with current
       • Laminated core
    4. State and explain two factors that determine the magnitude of induced emf in a coil rotating in a magnetic field.
       (2 marks)
       • Speed of rotation of the coil
       • The current in the coil
       • Strength of the magnet
       • Angle at which coil is cutting the magnetic field.
14.  
    1. State two factors that determine the speed of electrons emitted from a metal surface by light energy falling on it. (2 marks)
       • Energy of the incident radiation
       • Work function of the metal.
    2. The figure below shows the apparatus used to investigate photoelectric effect of a certain radiation.
       name the labelled parts A, B and C.      (3 marks)
       
       A-Cathode
       B-Anode
       C-photocell
    3. A photosensitive cathode of work function 2.1ev is irradiated by a radiation of wave length, 4.5 x 10^-7m(Take C = 3.0 x 10⁸ms⁻¹, h = 6.63 x 10^-34JS and 1ev = 1.6 x 10^-19J.)
       Determine:
       The stopping potential on the cathode. (e = 1.6 x 10^-19C)        (3 marks)
       Given the equation h^C/_A=W_o +ev_s 
       V_s =  0.6625
               1.6 × 10⁻¹⁹
       V_s= ^hc/_ed −w_o/e
       
       
       
    4. The graph below shows the stopping potential against frequency of the incident radiation of different colours of light on a photocell.
       
       From the graph determine the threshold wave length.    (2 marks)
       
15.  
    1. State two factors that affect the capacitance of a parallel plate capacitor.    (2 marks)
       • Distance between the plates
       • Overlap area of the plates
       • Dielectric material between the plates.
    2. The figure below shows an arrangement of capacitors connected to 12.0V d.c. supply.
       
       Determine;
       1. The effective capacitance.   (3 marks)
          
          =1μ + 3μF
          =4μF
       2. The total charge in the capacitors.     (2 marks)
          Q=CV
            =4 × 10⁻⁶F ×12V
            =4.8 × 10⁻⁵C
       3. The charge store in the 3μF capacitor.    (2 marks)
          Q=CV
            =3 × 10⁻⁶F × 12V
            =3.6 × 10⁻⁵C
          
          
16. The figure below shows a waveform on a CRO screen,
    
    Given that the y-gain control is set to 20V/cm and the time base set at 10ms/cm.
    Calculate;
    
    1. The peak voltage fed onto the y-plates.     (2 marks)
       20v/cm × 2cm =40
    2. The periodic time of the wave.     (2 marks)
       T=10ms/cm × 4cm =40ms
       T= ⁴⁰/₁₀₀₀s = 0.04s
    3. The frequency of the wave form.         (2 marks)
       f=¹/_T =¹/_0.04 =25HZ
    4. Explain what is meant by thermionic emission        (1 mark)
       • Emission of electrons from a metal surface when heated
    5. State two advantages of a CRO over conventional voltmeter.  (2 marks)
       • Infinite resistance hence no current flows through 
       • Can measure both ac and dc
       • Record results instantaneously
       • Can measure large voltages without damage
17. The figure below shows the common features of an x-ray tube.
             
    
    1. Name the parts labelled A and B.
       A - Copper Anode    (1 mark)
       B - Stream of electrons      (1 mark)
    2. What property of lead makes it suitable for use as shielding material?    (1 mark)
       • High density
    3. Explain how the intensity of the x-rays from such a tube may be increased.      (1 mark)
       • Increasing the cathode heating current
    4. If the x-ray tube is operated with an anode voltage of 10KV and a tube current of 160MA,
       Given
       • Charge of an electron = 1.6 x 10^-19C
       • Mass of an electron = 9.1 × 10^-31 kg.
       • Planck's constant = 6.63 x 10^-34JS
       • 1ev = 1.6 x 10^-19J.
         Determine the velocity of an electron striking the target.     (3 marks)
         ½mv² =ev
           mv²=2ev
           
18.  
    1. The figure below shows the path of a radiation from a radioactive source moving in a magnetic field perpendicular
       
       Identify the radiation.    (1 mark)
       
       • Using Fleming's left hand rule
         Alpha α
    2. Below is a nuclear equation for a fission process resulting from reaction on a neutron with a uranium nucleus.
       
       Determine the values of X and Y.
       X    36     (1 mark)
       Y     3      (1 mark) 
    3. Define the term half-life as used in radioactivity.   (1 mark)
       • Time taken for half the number of nuclides initially present in a radioactive sample to decay