Physics Paper 2 Questions and Answers - Samia Joint Mock Examination 2021/2022

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INSTRUCTIONS TO CANDIDATES

  • Write your name, index number, admission number and sign in the spaces provided above.
  • This paper consists of two sections A and B.
  • Answer all the questions in sections A and B in the spaces provided.
  • All workings must be clearly shown where applicable.
  • All numerical answers must be expressed in decimal form
  • Non-programmable silent electronic calculators and KNEC Mathematical tables may be used where applicable.

SECTION A (25 MARKS)
Answer ALL the question in this section in the spaces provided

  1. The figure below represents a point image formed by a mirror.
    1
    Sketch rays to show how the image is formed and seen by the eye. (2 mks)
  2. State any two ways of increasing the size of an image formed by a pinhole camera. (2 mks)
  3. A leaf electroscope A is charged and placed on a bench. Another uncharged leaf electroscope B is placed on the same bench and moved close to A until the caps touch each other. State and explain what is likely to be observed on the leafs of A and B. (2 mks)
  4. State one way in which polarization reduces the current produced by a simple cell. (1 mk)
  5. Using the domain theory of magnetism, explain why a bar magnet may lose its magnetism when hammered. (1 mk) 
  6. The figure below shows an image, I formed by an object placed in front of a convex mirror.
    2
    On the same diagram, draw appropriate rays and locate the object. (2 mks)
  7. The figure below shows two parallel thick copper conductors connected to a d.c power supply. A rider made from a thin copper wire is placed on the conductors as shown.
    3
    State and explain what is observed on the rider when the switch is closed. (2 mks)
  8. The figure below shows how the displacement varies with time for a certain wave.
    4
    Determine the frequency of the wave. (2 mks)
  9. The figure below shows a voltmeter connected across two charged parallel plates.
    5
    When a thin sheet of mica is inserted between the plates, the reading of the voltmeter is observed to reduce. Explain this observation. (2 mks)
  10. An electric heater is rated 240 V, 3000 W is to be connected to a 240 V mains supply, through a 10 A fuse. Determine whether the fuse is suitable or not. (3 mks)
  11. The figure below shows two identical copper coils P and Q placed close to each other. Coil P is connected to a d.c power supply while coil Q is connected to a galvanometer, G. 
    6
    1. State and explain what would be observed on the galvanometer immediately the switch S is closed. (2 mks)
    2. State the difference that would be noted in the observation made in (a) if the number of turns in coil Q were halved. (1 mk)
  12. The activity of iodine was found to be 1 024 counts per minute. After 80 days, the activity became 32 counts per minute. Determine the half-life of iodine. (3 mks)

SECTION B (55 MARKS)
Answer ALL the questions in this section in the spaces provided

  1.      
    1. State one difference between light and sound waves (1 mk)
    2. In determining the depth of a sea, an echo sounder produces ultrasonic sound. Give two reasons why this sound is preferred. (2mks)
    3. Explain how an increase in temperature affects the velocity of sound in air. (2 mks)
    4. The figure below shows a set up made by a Form 2 student to study an aspect of a wave.
      7
      1. State what happens to the sound from the bell as the bottle and its contents are cooled to 0°C (1 mk)
      2. Explain the observation in (i) above (2 mks) 
    5. A boy stands some distance from a high wall and claps his hands. He claps again each time he hears an echo.
      1. What two measurements would need to be made in order to determine the speed of sound? (2mks) 
      2. The boy’s friend notes that it takes 10 s to make 11 claps. Determine how far the boy is from the wall, given that the speed of sound in air is 330 m/s. (2 mks)
  2.      
    1. State Ohm’s law. (1 mk)
    2. With an aid of a diagram, describe an experiment to verify Ohm’s law for a wire. (4 mks)
    3. Two resistors, R1 and R2 are connected in series to a 10 V battery of negligible internal resistance. The current that flows in the set-up is 0.5 A. When R1 is connected alone to the battery, the current that flows is 0.8 A. Calculate:
      1. The value of R2 (3 mks)
      2. The current that flows when R1 and R2 are connected in parallel to the same battery (3 mks)
  3.      
    1. State two conditions necessary for total internal reflection to occur. (2 mks)
    2. The figure below shows the part of a ray of yellow light through a glass prism. The speed of yellow light in the prism is 1.88 x 108 m/s.
      8
      1. Determine the refractive index of the prism material (Speed of light in air, C = 3.0 x 108 m/s) (2 mks)
      2. Show on the figure the critical angle C, and determine its value. (3 mks)
      3. Given that r = 21.2º, determine angle θ. (2 mks)
    3. The figureshows two rays A and B entering a semi-circular glass block which has a critical angle of 42º. The rays are incident at point O.
      9
      1. Complete the path of the two rays from point O. Label A1 and B1 the corresponding rays. (2 mks)
      2. Calculate the refractive index of the semicircular glass block. (2 mks)
  4.      
    1.      
      1. State two properties of X — rays (2mks)
      2. In a certain X-ray tube, electrons are accelerated by a potential difference of 10KV. Assuming that 5% of the energy is converted into X — rays, determine the frequency of the X-rays produced. (h = 6.62 x 10-34Js , e = 1.6 x 10-19 C) (3mks)
    2. Describe how a P-type semiconductor is formed (3mks)
    3. Give one experimental observation which shows that each of the following is not an electromagnetic wave: (2 mks)
      1. Sound waves 
      2. Cathode rays 
    4. A source of radiation gives photons of energy 5.9 ×10-19 J. Calculate the wavelength of the photons (Planck’s constant, h = 6.23 ×10-34 Js and the speed of light, c = 3.0 ×108 m/s ) (2 mks)
  5.    
    1. State Lenz’s law of electromagnetic induction. (1 mk)
    2. A coil is moved quickly away from the end of a stationary magnet Y and current noted to flow asshown below.
      10
      1. Indicate on the same figure, the polarity at the end of the coil near the magnet Y. (1 mk)
      2. State the essential condition for emf to be induced in the coil above. (1 mk)
    3. A transformer has 800 turns in the primary winding and 40 turns in the secondary winding. The current in the primary is 0.2 A when connected to an alternating e.m.f of 240V. Find:
      1. The secondary e.m.f. (2mks)
      2. The power in the secondary if the transformer is 80% sufficient. (2mks)

MARKING SCHEME

  1.    
    11 
  2. Moving the object towards the pinhole (Reducing the object distance)
    Moving the screen away from the pinhole (increasing the image distance)
  3. Leaf divergence of A decreases while the leaf divergence of B increases
    Due to the repulsion of charges in electroscope A, some charges move to electroscope B
  4. Formation of hydrogen gas around the copper plate insulates the electrode.
  5. Hammering causes the dipoles to vibrate, making them lose their alignment
  6.    
    12  
  7. The rider moves to the left.
    The rider experiences a force when placed to a magnetic field according to Fleming’s left hand rule
  8. T=0.5 s
    f=1/0.5
    = 2 Hz
  9. the charges in the plates induces opposite charges at ends of the mica sheet
    the induced charges produce electric field that opposes the electric field due to the plates hence reducing the resultant electric field and since V = Ed, V reduces
  10. I= P/V
    =3 000
       240
    = 12.5 A The fuse is not suitable
  11.        
    1. the galvanometer deflects
      magnetic field in P builds up from zero to a maximum, cutting coil Q and inducing an e.m.f in it, hence current flows
    2. The deflection is also halved 
  12. N=N0 (½)T/t
      32   
    = ½80/t = ½5Accept alternative method
    1 024
    80/t=5
    t = 16 days

SECTION B (55 MARKS)

  1.      
    1. light is an electromagnetic/ transverse wave while sound is a mechanical/longitudinal wave
    2. it penetrates deepest
      it is easily reflected by tiny grains of sand
    3. An increase in temperature increases the kinetic energy of the air particles
      This leads to an increase in the speed of sound.
    4.    
      1. Sound becomes less audible until it cannot be heard any more.
      2. Steam condenses, creating a (partial) vacuum in the jar.
        Sound, which requires material media for transmission, will not be heard.
    5.      
      1. the distance between the boy and the wall
        the time taken to hear the echo
      2. time for 1 clap = 10/10=1 s
        d= ½ ×330 ×1
        = 165 m
  2.      
    1. The amount of current flowing through a conductor is directly proportional to the potentialdifference across its ends, provided that temperature and other physical conditions arekept constant.
    2.      
      13    
      • Close the switch and adjust the rheostat to obtain the value of current, I and the corresponding value of voltage, V. Record the values in a table.
      • Repeat the experiment for other values of I and the corresponding values of V.
      • Plot a graph of V against I. The graph should be a straight line through the origin
    3.      
      1. 0.8 R1=10
        R1= 12.5 Ω
      2. 0.5 (12.5+ R2)=10
        12.5+R2=20
        R2=7.5 Ω
      3. R=7.5 ×12.5=4.688 Ω
             7.5+12.5
        I= 10/4.688
        = 2.133 A
  3.      
    1. the angle of incidence in the optically dense medium is greater than the critical angle
      the ray must be travelling from optically dense medium to optically less dense medium
    2.      
      1. n = c/V
        = 3.0 × 10 3
          1.88 × 108
        = 1.5957

      2. 14
        sin⁡c=1/n=1/1.5957
        c = sin-1(1/1.5957) = 38.81º
      3.   sin ⁡i    = 1.5957
        sin⁡21.2° 
        θ = sin-1 (1.5957 sin 21.2°) = 35.24°
    3.          
      1.    
        15   
      2. n = 1/sin⁡42°
        = 1.4945
  4.      
    1.      
      1. To travel at the speed of light in a vacuum
        • Cause some substances to fluoresce
        • Undergoes diffraction, Refraction, interference
        • Penetrates matters
        • Obeys the wave equation
      2. K.E = eV = hf
        f = eV/h x 5 % = 1.6 x 10-19 x 10000x5/60620x 10-34 x 100
        f = 1.208 x 1017 Hz
    2. Dope a group 3 element with a pure semiconductor
      3 outermost electrons from the group 3 element form bonds with their neighbours leaving a hole which acts as a positive charge.
      This creates P type (positive charge) semiconductor
    3.      
      1. Sound wave – cannot travel in a vacuum
      2. Cathode rays – are deflected by both magnetic and electric fields
    4. E =hc/λ
      λ = 6.23 × 10-34 × 3.0 × 10
                      5.9 × 10-19
      = 3.168 ×10-7m
  5.      
    1. the direction of induced current is such that it opposes the change causing it
    2.      
      1. North (N)
      2. Change of flux linkage
    3.      
      1. NP = 800, NS = 40
        VP = 240v, IP= 0.2A
         NS = V40 = VS
         NP    V800  240
        VS = 12 V
      2.  Power out  ×100%=80%
        power input
        P= (100% (240v)(0.2)×80)
                           100%
        = 38.4N

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