Physics Paper 2 Questions and Answers - Lainaku 1 Joint PreMock Exams 2023

• Attempt ALL questions in sections A and B.
• All working must be clearly shown

                                                                                         SECTION A: (25 MARKS)

1. An incident ray makes an angle of 25° to the mirror as shown below.
   Fig 1
                                       
   Complete the diagram to show how the ray is reflected after striking the mirror hence calculate angle of reflection.        (2 mks)
2. Give the reason why insulators do not conduct electric current.          (1 mk)
3. A positively charged glass rod is brought near the brass cap of a negatively charged electroscope. Explain why the leaf falls.        (2 mks)
4. What causes a freely suspended magnetic needle to always point in the north south direction?             (1 mk)
5. A ray of light travelling towards a concave mirror passes through its centre of curvature. State how the ray is reflected after striking the mirror. (1 mk)
6. Fig 2 below shows a magnetic compass placed near a conductor in an electric circuit.  
                                        
   1. State what happens to the magnetic needle when the switch is closed. (1 mk)
   2. Explain why the needle behaves as described in (a) above. (1 mk)
7. What are longitudinal waves. (1 mk)
8. An echo sounder in a ship produces a sound pulse of frequency 24.8 KHZ. An echo is received from sea bed at a depth of 175m after 0.25 seconds. Calculate the wave length of sound in water.                      (3 mks)
9. The critical angle of a ray of light travelling from medium A to air is 44°.
   1. Define the term critical angle. (1 mk)
   2. Calculate the angle of refraction, when the angle of incidence is decreased to 400 (give your answer to 3 decimal places.)  (3mks)
10. A circular wave is incident on a straight reflector as shown in fig 3 below.
                                                     
    Complete the diagram to show how the wave is reflected.         (2 mks)
11. Fig 4. Below shows a circuit consisting of capacitors and a battery
                                                                
    Determine the charge stored in the circuit (3mk)
12.  
    1. Sketch a graph to show the variation of the current against time for a discharging capacitor in axis below. (1 mk)
                                                   
    2. State two ways of increasing the capacitance of a capacitor. (2mk)

                                                                               SECTION B (55 MARKS)

13.  
    1. State two factors that determine the heat produced by a conductor when connected to an electric circuit. (2mks)
    2. The electrical power is given by
       P = V I   where V = Pd across a conductor
                                 I = Current through a conductor.
       Show that electrical power can also be given by
       
       P = V²/R where R=resistance.                    (3 mk)
    3. What property does a fuse wire have that makes it suitable for its use in a circuit.  (1 mk)
    4. An electric heater rated 1.2 KW, 240V supplies 5.5 x 10⁵ joules of heat energy to water in an insulated container.
       1. For how long is the heater switched on.(Give your answer in minutes and to 2 decimal places)           (3 mks)
       2. Determine the resistance of the heater coil            (2 mks)
14.  
    1.  
       1. Using a ray diagram show how a convex lens forms an image when an object is placed between it and its focal point.   (3 mks)
       2. Name one optical device that makes use of the above set up.   (1 mk)
    3. In an experiment to determine the focal length of a converging lens, several values of image distance V and corresponding values of object U were obtained.
       

       Object distance (U) cm	10	15	20	25
       Image distance (V) cm	40.0	17.1	13.3	11.8
       1/U x 10-2 (cm-1)
       1/v x 10-2 (cm-1)

       
       
       1. Complete the table.            (2 mks)
       2. Plot a graph of ¹/_v against ¹/_U and produce it to cut both axis      (4 mks)
                      
       3. Find the intercepts at ¹/_u.    = _______________ (cm^-1)        (1 mk)       
                                                          ¹/_v    =   ______________ (cm^-1)                       (1 mk)                                                 
       4. Determine the average value of focal length of the lens from the graph           (2 mks)
15.  
    1. The table below shows an arrangement of electromagnetic spectrum.
       

       Radio waves

       Micro waves

       A

       Visible light

       B

       X rays

       Gamma rays

       
       
       1. Name the radiation represented by B. (1mk)
       2. Name the human organ that detect radiation A. (1mk)
       3. State one application of gamma rays. (1mk)
    2. Fig 5. Shows a dry cell (the paper that covers the dry cell is not shown)
       
       1. Name the parts labelled A and B
          1.           (  1mk)
          2.        ( 1mk)
       2. State and explain the importance of manganese (iv) oxide in the cell (2mks)
       3. Explain why large currents should not be drawn from the cell for a long time (2mks)
    3. State with reasons whether the dry cell is classified as primary or secondary type of cell          (2mks)
16.  
    1. Explain what is meant by non-Ohmic conductors (2mks)
    2. State the reason why electromotive force of a cell is always higher than the potential difference (terminal voltage) (1mk)
    3. Fig 6, below shows three identical bulbs A, B, and C connected in a series – parallel circuit.
                                                            
       1. State the bulb with the highest potential difference. (1 mk)
       2. If current through Bulb B is 0.85A, determine the current through bulb A.                 (2 mks)
    4. State two factors that affect a resistance of a metal conductor    (2mks)
    5.  
       1. In the axis provided below sketch a graph to show the relationship between the resistance( R) and temperature of a thermistor (1mk)
                                               
       2. Explain the curve of your graph in (e) (i) above. (1mk)
17.  
    1. What is meant by the term diffraction of a wave (1mk)
    2. State two factors that determine the extent of diffraction of a given wave          (2 mks)
    3. Two identical loudspeakers connected to the same audio-frequency generator are placed some distance away from each other as shown below.
                                                            
       1. Briefly describe the sound experienced by:
          1. An observer moving along line AB.           (1mk)
          2.  
             1. An observer moving along CD.               (1mk)
             2. Explain the sound experienced by the observer in (b (i)) above           (2mks)
          3.  
             1. State with reason the effect of increasing the frequency of the audio generator on the sound heard along line CD (2mks)

                                                                                    MARKING SCHEME

1. Fig (1)
                                      
2. Because their electrons are tightly bound to the nuclei of the atoms and are not free to move.
3. The positively charged glass rod attracts some electrons from the leaf and metal plate towards the brass cap hence decreasing the charge at leaf and plate.
4. Because of earths magnetic field. / The earth behaves as though it has a magnet inside.
5. The ray is reflected along the same path.
6.  
   1. The magnetic needle gets deflected.
   2. When current passes through the conductor magnetic field forms around it which interacts with that of magnetic needle causing a deflection.
7. They are the waves in which the direction of the particles is parallel or along the direction of wave travel.
8.  
                                                        
9.  
   1. The angle of incidence in the denser medium for which the angle of refraction in the less dense medium is 90° .
   2.          refractive index = 1/sin c
                                        = 1/sin 44°
                                        = 1.44
      When,   i = 40°
      Refractive index = sin 40° /sin r
                      Sin r   =  sin 40°/1.44
                                = 0.446
                              r = 26.5°
10.  
                                                       
11.          
                        Q = CV
                        Q = (25 x 15)/ (25 + 15) µF  x  6V
                        Q = 56.25µC
12.  
    1.  
                                               
    2.  
       1. Decreasing of distance of separation of plates.
       2. Increasing of area of overlap of plates.

                                                                                                   SECTION B

13.  
    1.  
       • Amount of current
       • Resistance of conductor
       • Time taken.  (any 2)
    2. P = VI
       But I =V/R
       Therefore P = V (V/R)
                        P = V² /R
    3. Low melting point.
    4.  
       1. Heat = power x time
          5.5 x10⁵ J = (1.2 x 1000) W x t
                         t = 458.33 s
                         t = (458.33/60) minutes
                         t = 7.64 min
       2. P = V²/R
          R = 240²/( 1.2 x 1000)
          R = 48 Ω
14.  
    1.  
       1. 
                                     
       2. Magnifying glass/microscope
    2.  
       1.  
          

          Object distance (U) cm	10	15	20	25
          Image distance (V) cm	40.0	17.1	13.3	11.8
          1/U x 10-2 (cm-1)	10.0	6.7	5.0	4.0
          1/v x 10-2 (cm-1)	2.5	5.8	7.5	8.5

       2.  
          • Labelling axis   --- (1 mk)
          • Scale ---- (1 mk)
          • Plotting points--- (1 mk)
          • Straight line --- (1 mk)
       3. ¹/_u. = 12.2 x 10^-2 (cm^-1)               
          ¹/_v  = 12.3 x 10^-2 (cm^-1) 
       4. Average focal length = (f₁ + f₂)/2
          But,     f₁ = 1/ (12.2 x 10^-2 )
                     f₁ = 8.2 cm
                     f₂  = 1/(12.3 x 10^-2 )
                     f₂  = 8.13 cm
          average focal length = (8.2 + 8.13)/2
                                           = 8.165 cm
15.  
    1.  
       1. ultra violet radiations
       2. skin
       3. To kill tumors and cancerous cells
    2. 1. 1. Zinc can
          2. Ammonium chloride jelly( or paste)
       2. • Its importance is to depolarize.
          • It removes hydrogen gas around the carbon rod by reducing it to water.
       3. The process of depolarization is slow hence some hydrogen is left at the carbon rod causing insulation.
    3.  
       • It’s is a primary cell
       • It cannot be recharged
16.  
    1. The materials in which voltage across is not directly proportional to current flowing since they do not obey Ohms law.
    2. Some of the cells energy is used to drive current through the internal resistance of the cell.
    3.  
       1. Bulb A.
       2. Current = 0.85 A x 2
                       = 1.7 A
    4.  
       • cross section area
       • length of conductor
       • nature of the material
       • temperature   (any 2)
    5.  
       1.  
                                                      
       2. The resistance of a thermistor decreases with increase in temperature
17.  
    1. speading of a wave after passing through a gap or an obstacle.
    2.  
       • size of wavelength.
       • size of gap
    3. 1.  
          1. The observer hears loud sound all through
          2.  
             1. The observer hears alternating loud and soft sound
             2. A loud is heard when there is constructive interference and a soft sound when there is destructive interference.
    4.  
       1. Distances between the points of constructive interferences (loud sound) is reduced and also those of destructive interferences (soft sound) are reduced.
       2. Because higher frequency signal has shorter wavelength.