PHYSICS PAPER 2 - 2019 KCSE CEKENA MOCK EXAMINATION (QUESTIONS AND ANSWERS)

Instructions to candidates.

• This paper contains two sectionsA and B.
• Answer all questions in both sections A and B.
• KNEC Mathematical tables may be used.
• Silent,non-programmed ,electronic  calculators may be used where necessary.
• All working MUST be clearly shown.
• Where necessary,take g=10N/Kg,speed of light c= 3.0 x 10⁸ ms¹

Answer all the questions in this section 
SECTION A (30MKS)

1. State the laws of reflection            (2marks)

2. Draw the magnetic field around the two conductors  shown below.                   (2mark) 
                                                                                                                                          

3. Give a reason why attraction in magnetism is not regarded as a reliable method of testing polarity of a magnet.            (2marks)

4. State two advantages of using a convex mirror as a driving mirror.                    (2marks)

5. State two advantages of an alkaline accumulator over lead acid accumulator.                (2mks)

6. The figure below shows iron bar rod AB inside a coil of a wire. When the current flows through the coil in the direction shown. Identify the polarity of end A and B.         (1mk)
   

7. The figure below shows how magnets are stored in pairs with keepers at the end.
   
   
   1. Name the most suitable metal used to make the keepers         (1 mk)
   2. Explain how the metals above help in retaining magnetism longer.                                 (1 mk)

8. State the two conditions necessary for total internal reflection to occur.            (2marks)

9. The filament of an electric lamp is made of tungsten.  Why is tungsten a satisfactory material for the lamp filament?  (1mark)

10. The chart below shows an arrangement of electromagnetic spectrum.
    

    radio waves

    A

    infra-red

    visible light

    B

    x-rays

    gamma rayrs

                                                                                                               
    1. Name the radiation represented by A(1mark)
    2. Name the device that can be used to detect radiation B (1mark)

11. Two similar razor blades were placed on a wooden block and the other on an iron block as in figure 10.
    
    It was observed that the razor blade on the wooden block is attracted by the magnet while that on the iron block was not. Explain.  (2 marks)

12. The following shows a displacement time graph of a wave.  The velocity of the wave is 40cm/s
    Determine the:                                                     
    1. Period                     (1 marks
    2. Frequency                (2 marks)
    3. Wavelength             (2 marks)

SECTION B (50MKS)

13.  
    1. Explain why is not advisable to carry a pointed umbrella when it’s raining.  (2 mks)
    2. State one factor which affects the capacitance of a capacitor.       (1 mark)
    3. State one use of leaf electroscope          (1mark)
    4. Explain how capacitor C, in the figure below is     
                                                                                         
       1. charged        (2mark)
       2. Discharged          (2mark)
    5. The figure below shows electrical circuit with three capacitors A, B and C of capacitance 5 μF, 6 μF and 3 μF respectively connected to a 12 V battery.
       
       Determine:
       1. The combined capacitance of the three capacitors           (3 marks)
       2. The charge on the capacitor C             (2 marks)
       3. The potential difference across the capacitors B.                                          (2 marks)

14.  
    1. state Snell’s law      (1mark)
    2. A ray of light travels from air into medium 1 and 2 as shown
       
       Calculate
       1. The refractive index of medium 1.                                                                    (2mark)
       2. The angle of refraction r2 in medium two given that the refractive Index of medium 2 is 1.33.                  (3marks)

15.  
    1.  
       1. State Ohm’s law                                                                                         (1 mark)
       2. Two resistors R1 and R2 are connected in series to a 10V battery. The current flowing then is 0.5 A when R1 only is connected to the battery the current flowing is 0.8A. Calculate the
          1. Value of R2           (3 marks)
          2. Current flowing when R1 and R2 are connected in parallel with the same battery.                     (2 marks)
       3. Recharging is one of the practices and maintenance of accumulators. State one measurement, which need to be taken to help you decide when an accumulator is due for charging.                     (1 mark)
    2. In the circuit diagram A, B, C, D, E, F and G are identical lamps.
       
       
       1. Explain which lamps are the brightest and which are the dimmest.                     (2 marks)
       2. If the circuit breaks between lamps B and F, explain the change of brightness in the other lamps.  (3 marks)

16. A lens forms an image that is four times the size of the object on a screen. The distance between the object and the screen is 100cm when the image is sharply focused.
    1. State with reasons what type of lens was used.                                                         (2mks)
    2. Calculate the focal length of the lens.            (4mks)
    3. The figure below shows a human eye with a certain defect.
       
       
       1. State one cause of this defect.                 (1 mark)
       2. On the same diagram, sketch the appropriate lens to correct the defect and sketch rays to show the effect of the lens.    (2 marks)
    4.  
       1. State why convex mirrors are used in supermarkets to check shoplifters. (1mk)
       2. State 3 similarities between the eye and the camera.    (3mks)

17.  
    1. Use the figure 11 below to answer the questions that follows.
       
       
       1. Show the direction of the current on the turns when the switch S is closed.   (1marks)
       2. State the polarity at P                                                                                    (1marks)
       3. Explain using domain theory what happens on the soft iron bar.                (1marks)
       4. If steel bar was used instead, what could be the difference?                       (2marks)
    2. The following diagram (figure 12), shows a part of an electric d.c motor.
       
       
       1. On the diagram above show the direction of rotation of the coil.                  (1marks)
       2. State the effect of increasing the number of turns of the rotating coil of an electric motor.(1marks)
    3. Sketch the magnetic field pattern around the conductor carrying current on figures 13 and 14 shown below. (2marks)
       

MARKING SCHEME

1. The incident ray the reflected ray and the normal at the point of incidence lay on same plane.
2. The angle of incidence is equal to the angle of reflection
   

3. Since attraction can occur between a pole and a magnetic material, While repulsion between two like poles only.
4. -forms upright image-wide field of view

5.  
   • Alkaline produces higher current
   • Lasts longer
   • It is portable
   • Less maintenance and care

6. A- South
   B- North

7. –iron metals
   -Keepers get magnetised by induction acquiring opposite poles that make them get attracted to the magnet forming a closed loop in dipoles.

8. State the two conditions necessary for total internal reflection to occur. (2marks)
   • Light should travel from optically denser to less dense medium
   • Incidence angle greater than critical angle

9. High melting point
10.  
    1. A- Micro wave
    2. Photographic film, photocell, fluorescent materials
11. The magnet induces magnetism into the razor√1mark which in turn Induces the iron block√1mark hence the razor remains attracted to the iron block.

12. The following shows a displacement time graph of a wave. The velocity of the wave is 40cm/s      
    Determine the:                                                                         
    1. T = 0.12 seconds
    2. f= ¹/_T=¹/_0.12=8.333hz
    3. wavelength= ^V/_F= ^0.4/_8.333 = 0.048m                                                                          

Section B (55mks)

13.  
    1. Sharp points readly attract charges from the cloud and can easily conduct them to the ground through the body, this leads to electrocution.
    2. –area of overlap
       - Distance of separation.
       - Nature of dielectric material
    3. –detecting prescence of charge
       - detecting the type of a charge
       -Detecting quantity of charge
       -insulation property
    4.  
       1. charged                                                                                                 
          By connecting B to A, current flow which in turn charges the capacitor
       2. Discharged
          by connecting B to D and the capacitor acts as the source of energy
    5.  
       1. = 2.933 ȗF
       2. Q = CV= 2.933ù x 12 = 3.5196 x 10 ^-5coulombs
       3. p.d = 3.201 v

14.  
    1. Snell’s law                                                                            
       the ratio of sine of angle of incidence to the angle of refraction is constant for a pair of medium
    2. A ray of light travels from air into medium 1 and 2 as shownCalculate
    3.  
       1. ^sinsin40/_{sin 24}= 1.58
       2. n₁sinØ1 ₌ n₂sinØ₂
          1.58sin 24 = 1.33sin Ø₂
          sin Ø₂= 0.4832
          Ø₂= 28.89⁰

15.  
    1.  Ohm’s law
       The current flowing through a conductor is directly proportional to the potential difference across it provided temp and other physical conditions are kept constant.                                          
    2. Two resistors R₁ and R₂ are connected in series to a 10V battery. The current flowing then is 0.5 A when R₁ only is connected to the battery the current flowing is 0.8A. Calculate the
       1. Value of R₂                                                                
          V= IR
          10 = 0.5(R₁+ R₂)
          10 = 0.8R₁
          R₁ = 12.5
          10 = 0.5(12.5+ R₂)
          R₂= 20- 12.5= 7.5
       2. I = 2.133 A
       3. Measuring the level of liquid
          Measuring the density of the liquid
          (any one correct)                                                                         
    3. A &G are brightest since they don’t share current
       C & D are dimmest since the current is split.
       Bulbs A, E and G will light with the same brightness. C & d will also be off.

16.  
    1. Converging lens√, this is because the image formed is real√
    2. m=v/u√
       v=4u
       u+v=100√
       u+4u=100
       5u=100
       u=20cm
       v=80cm√
       ¹/_F = ¹/_U + ¹/_V
       F=16cm  
    3. Cause – Eye lens having a short focal length. Or - Eyeball being too long.       Any one (1mk)
    4.  Correct rays ✓¹
       
    5. The have a large field of view. √ 
    6.  
       

       Eye	Camera
       Eye has a crystalline convex lens	Camera has a convex lens
       Eye has retina where images are formed	Camera has a light sensitive film where images are formed
       Iris controls the amount of light entering the eye	The diaphragm controls the amount of light entering the camera.
       Choroid layer of the eye is black	Camera box is painted black inside.

               

17.  
    1.  
       1.  
          √1mark
       2. P is South Pole. √1mark
       3. Dipoles in the domain are aligned in the process of magnetisation. √1mark
       4. Steel retains magnetism than soft bar
          Steel will also take longer to be magnetized. √1mark
    2.  
       1.  
          √1mark
       2. Increase the power of the electric motor. √1mark
    3.