Physics Paper 2 Questions and Answers - Kassu Jet Joint Exams 2020/2021

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232/2
PHYSICS
PAPER 2
TIME: 2 HOURS

Instructions to candidates

  • This paper consists of two sections A and B.
  • Answer all the questions in the two sections in the spaces provided after each question
  • All working must be clearly shown.
  • Electronic calculators, mathematical tables may be used.
  • All numerical answers should be expressed in the decimal notations


QUESTIONS

SECTION A: (25 MARKS)

  1. Explain why repulsion method is the best test for polarity of a magnet as opposed to attraction. (1 mark)
  2. Define the following;
    1. the direction of an electric field. (1 mark)
    2. the capacitance of a capacitor. (1 mark)
  3. The diagram below shows a set of parallel rays of light incident on a thin lens and emerging out from the lens. The lens is placed inside a blackbox with narrow opening on both sides.
    phyp2 q3 kassu2021
    State the type of the lens in the box and explain your answer. (2 marks)
  4. In an experiment to magnetize two substances P and Q using electric currents, two curves were obtained as shown below.
    phyp2 q4 kassu2021
    1. Explain the difference between substances P and Q with reference to domain theory. (1 mark)
    2. State and explain which of the two substances in (i) above would be suitable for use as a core of an electromagnet. (1 mark)
  5. The letters in the figure below represents different types of radiations in the electromagnetic spectrum.
    phyp2 q5 kassu2021
    1. Which colours of spectrum appears at P and Q?
      P - …………………………………………… (1 mark)
      Q - …………………………………………… (1 mark)
    2. How is radiation marked C detected? (1 mark)
  6. The diagram below shows a circuit that was connected by a form one student. Comment with a reason on the brightness of the bulbs. (2 marks)
    phyp2 q6 kassu2021
  7. A car battery requires topping up with distilled water occasionally. Explain why this is necessary and why distilled water is used. (2 marks)
  8. The figure below shows the wiring in a modern mains appliance.
    phyp2 q8 kassu2021
    Identify the wires X, Y and Z. (2 marks)
    X - …………………………………………………………………………………………………………
    Y - …………………………………………………………………………………………………………
    Z - …………………………………………………………………………………………………………
  9. Three resistors of resistance 2.0Ω, 4.0Ω and 6.0Ω are connected together in a circuit. Draw a circuit diagram to show the arrangement to the resistors which gives;
    1. An effective resistance of 3.0Ω (2 marks)
    2. A minimum resistance. (1 mark)
  10. When rod X was rubbed with material Y, it was observed that the material acquired a negative charge.
    1. State the charge on the rod X. (1 mark)
    2. Explain how the rod X acquired the charge. (1 mark)
    3. Explain briefly how you would test the nature of the charge on rod X using an electroscope. (2 marks)
  11. Distinguish between intrinsic semi-conductor and extrinsic semiconductor. (2 marks)

SECTION B: (55 MARKS)

  1. The following figure shows a circuit where a battery of an e.m.f. 12v, switches A and B, two capacitors C1 = 9.0μF and C2 = 3.0μF and a voltmeter connected as shown below.
    phyp2 q12 kassu2021
    1. Determine the charge on C1 when the switch A is closed and B open. (2 marks)
    2. What is the voltmeter reading when switch A is closed and switch B open? (Assume capacitor C1 is fully charged). (1 mark)
      Switch A is now opened and switch B closed. Determine:
    3. The effective capacitance of C1 and C2. (2 marks)
    4. The voltmeter reacing V. (3 marks)
    5. The energy stored by C1 (2 marks)
  2.  
    1. In an experiment to study one of the properties of waves, a double slit was placed close to the source of monochromatic light as shown below.
      phyp2 q13 kassu2021
      1. What property of waves is being investigated? (1 mark)
      2. State the function of the double slit. (1 mark)
      3. State and explain the observation made on the screen. (2 marks)
      4. State what is observed on the screen when;
        1. the slit separation S1 S2 is decreased. (1 mark)
        2. White source of light is used in place of monochromatic source. (1 mark)
        3. S1 and S2 are made larger. (1 mark)
    2. The diagram below shows plane wave fronts in a ripple tank incident on a boundary between a deep to shallow region.
      phyp2 q13b kassu2021
      On the same diagram, sketch the wave pattern in and beyond the shallow region. (2 marks)
    3. The equation below represents a nuclear decay. (1 mark)
      phyp2 q13c kassu2021
      Identify the radiation A.
  3.  
    1. The diagram below shows an object O placed infront of a concave mirror as shown.
      phyp2 q14a kassu2021
      1. Complete the diagram to show the image formed. (2 marks)
      2. State two characteristics of the image formed. (1 mark)
    2.  
      1. State two factors that determine the speed by which electrons are emitted from metal surface by light falling on it. (2 marks)
      2. In an experiment using a photocell, light of varying frequency but constant intensity was shone onto the surface of a metal. The maximum kinetic energy, (Ke)max emitted for each frequency, was determined. The graph below shows how Kemax varies with frequency f. 
        phyp2 q14b kassu2021
        From Einstein’s equation, hf = Ɵ + Kemax, where Ɵ is the work function. Determine.
        1. the threshold frequency, f0 from the graph (1 mark)
        2. the planks constant, h (2 marks)
  4.  
    1. An electric cooker has an oven rated 3KW, a grill rated 2KW and two rings each rated at 500W. The cooker operates from 240V mains. What is the cost of operating all the parts for 30 minutes if electricity cost Ksh.6.50 per unit? (3 marks)
    2. Fig. below shows identical copper coils A and B placed close to each other. Coil A is connected to a d.c. power supply while coil B is connected to a galvanometer.
      phyp2 q15b kassu2021
      1. State and explain what is observed on the galvanometer when the switch is closed. (2 marks)
      2. State what is observed on the galvanometer when the switch is opened. (1 mark)
      3. State what would be observed if the number of turns of coil B is doubled. (1 mark)
    3. A transformer with 2000 turns in the primary circuit and 150 turns in the secondary circuit has a primary circuit connected to a 800V ac source. It is found that when a heater is connected to the secondary circuit, it produces heat at the rate of 1000w. Assuming 90% efficiency, determine the;
      1. Voltage in the secondary circuit. (2 marks)
      2. the current in the primary circuit. (2 marks)
      3. Current in the secondary circuit (1 mark)
    4. A cell drives a current of 5A through a 1.6Ω resistor. When connected to a 2.8Ω resistor, the current that flows is 3.2A. Determine the e.m.f. (E) and internal resistance (r) of the cell. (4 marks)
  5.  
    1. State how each of the following can be increased in an x-ray tube.
      1. Intensity of x-rays. (1 mark)
      2. penetrating power of x-rays. (1 mark)
    2. An x-ray tube has an electron beam current of 10mA and is accelerated through a p.d of 60KV. The efficiency is 0.5%. Calculate;
      1. the input power (2 marks)
      2. the quantity of heat produced per second. (1 mark)
      3.  the number of electrons hitting the target per second. (2 marks)
    3. The fig. below shows an a.c. signal on the C.R.O screen.
      phyp2 q16 kassu2021
      Determine:
      1. The frequency of the signal given that the time base is set at 10ms/div. (2 marks)
      2. The peak voltage of the signal given that the y-gain is set at 50v/div (2 marks)


MARKING SCHEME

  1. Repulsion occurs only between like poles. Attraction occurs between unlike poles and also between a magnet and a magnetic material
  2.  
    1. The path followed freely by a free +ve charge
    2. Charge stored per unit volt (C= Q/V)
  3. Concave lens
    - Rays parallel and close to the principal axis appear to diverge from the principal focus when refracted.
  4.  
    phyp2 ans4 kassu2021
    1. Dipoles in P align easily (easily magnetised) than those in Q (i.e. P is easily magnetised than Q)
      TOo magnetise them to the same strength, P requires less current than Q
    2. P - it s easily magnetised than Q or 
      - It is magnetically soft
  5.  
    1. P - red, Q - violet
    2.  Thermopile, bolometer, ckin thermometer with blackened bulbs
  6. The bulbs do not light. no current flow since the voltmeter is wrongly connected. The voltmeter should be out of the circuit not in the circuit i.e it should be connected across the device whose voltage is to be determined
  7. - Replace water lost due to evaporation when the cell is working
    - Distilled water is used since it doesn't have ions that can react with the acid to form insoluble compounds
  8. X - Live wire 
    Y- Neutral wire
    Z - Earth wire
  9.  
    1.  
      phyp2 ans 9i kassu20 0HGXQ
    2.  
      phyp2 ans 9ii kassu2 bm8qx
  10.  
    1. Positive charge
    2. During rubbing electrons were transferred from rod X to the material
    3. - Charge the electroscope +vely
      - Bring the rod close to the cap of the electroscope
      - Lok for an increase in the divergence of the leaf. This will confirm that X is +vely charged
  11. Intrinsic semi-conductor is a pure semiconductor while extrinsic semi-conductor is an intrinsic semi-conductor that has been doped i.e impurity has been added to improve conductivity
  12.    
    1. Q= C1V = 9 × 10-6 × 12 = 1.08 × 10-4 C
    2. V = 12 V when fully charged
    3. CE = 9 + 3 = 12 μF
    4. V = Q/C 
      = 1.08 × 10-4
          12 × 10-6
      = 9 V
      Or
      V = Q/C 
      108μC
          12μF
      = 9 V
    5. E1 = 1/2CV2 = 1/2 × 9 × 10-6 × 92
      = 3.645 × 10-4 J
  13.  
    1.  
      1. Interference of light
      2. Acts as a coherent source of light
      3. - Alternate bright and dark fringes are seen on the screen
        - Bright fringes are points where constructive interference occurs i.e. crest from one source meets a crest from the other source and where a crest from one meets a trough from the other, destructive interference occurs representing dark fringes 
      4.  
        1. Separation of fringes increase
        2. Central fringe is white, fringes on either side are coloured
        3. No fringe and therefore no interference
    2.  
      phyp2 ans13b kassu20 r4hgt
  14.  
    1.  
      1.  
        phyp2 ans14a kassu20 CiCp5
      2. Virtual, upright, magnified, behind the mirror
    2.  
      1. - Frequency pf incident radiation/wavelength
        - Work function of the metal surface/ type of metal
      2.  
        1. 4.45 × 1014 Hz
        2. h = (13.2 − 0) × 10-20  = 6.439 × 10-34Js
                (6.5 − 4.45) × 1014
  15.  
    1. Total power = 3kW + 2kW × ((2 × 500)/100) = 6 kW
      Total units (kWh) = 6kW × 30/60 hr = 2kWh
      if 1 Unit = sh 6.50
      ∴ 2 units = ?
      = 2 × 6.50 = Ksh 13.00
    2.  
      1. - The galvanometer shows a deflection in one direction then returns to zero mark
        Closing the swithc causes a change in the magnetic flux in the primary coil which links with secondary coil, inducing an emf and current in secondary coil. Both emf and current lasts for only a short time because as long as the switch is closed, the magnetic flux in the primary coil remains constant.
      2. The pointer will deflect in the opposite direction and then returns to zero mark
      3. he pointer will deflect more
      1. Vs = Ns ⇒ Vs = 150 × 800 = 60V
        Vp    Np               2000
      2. Pp = Ps/0.9 = 1000/0.9 = 1111.1 W
        Ip = 1111.1/800 = 1.389A
        or
        n = Po/PI
        90/100 = IsVs/IpVp
        0.9 =   1000   
                 Ip × 800
        Ip   1000    
               0.9 × 800
        = 1.389A
      3. Po = IsVs
        1000 = Is × 60
        Is = 1000/60 = 16.67 A
    3. E = I(R+r)
      E = 5(1.6+r) -------(i)
      E = 3.2 (2.8+r) ----(ii)
      5(1.6+r) = 3.2(2.8+r)
      8+5r = 8.96 + 3.2r
      1.8r = 0.96
      r = 0.96/1.8
  16.  
    1.  
      1. Increasing the heating current
      2. Increasing the anode voltage
        Increasing speed of electrons
    2.  
      1. P = Ir = 10 × 10-3 × 60 × 103 = 600W
      2. H = 99.5/100 × 600 = 597 W
      3. n = Q/e = It/e10 × 10-3 
                                1.6 × 10-19
        = 6.25 × 1016 electrons
    3.  
      1. f = 1/T
               1           
           4 × 10 × 10-3
        = 100/4 = 25 Hz
      2. Vo = 3 × 50 = 150 V

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