Physics Paper 2 Questions and Answers - Lugari Constituency Joint Pre Mock Exams 2023

1. Two plane mirrors are inclined at an angle of 120° to each other such that their reflecting surfaces face each other. An object pins stands midway between the mirrors. Draw a ray diagram to show all the images (3mks)
2. State two conditions necessary for the occurrence of an annular eclipse (2mks)
3. The figure below shows two parallel rays incident on a concave mirror. F is the focal point of the mirror
                                                     
   Sketch on the same diagram the path of the rays after striking the mirror. (2mks)
4. State the class of waves to which sound belongs (1mk)
5. Calculate the value of the critical angle C shown in the figure below (2mks)
                            
6. In the diagram below, two electroscopes A and B carry same type of charges as shown. The two are then connected with a copper wire as shown.
                                
   
   State and explain the observations (2mks)
7. The figure below shows a real image I formed by a convex lens
    
   On the same grid, construct a ray diagram to locate the position of the object (2mks)
   
   
8. State a property of electromagnetic wave on which the operation of a radar system is based (1mk)
9. The figure below shows an attempt to supply each of the three lamps L1,L2 and L3 with a switch.
                                         
   1.  Explain why this is a poor connection             (1mk)
   2. Redraw an adjacent diagram to show the best positioning for the switches (1mk)
10. State one use of x-ray in medicine and one use in industry (2mks)
11. Draw the magnetic field lines due to the configuration shown below (1mk)
    
12. Sketch the current –voltage characteristic of a junction diode in a forward bias mode (1mk)
13. The graph below represents values of ¹/_f  and corresponding values of wavelength for waves transmitted in a certain medium
    
    From the graph, determine the speed of the waves (3mks)
14. State one causes of power loss in long distance transmission wires and how these loses can be minimized (1mk)

                                                                                  SECTION B    (55 MKS)

                                                                   Answer all questions in the spaces provided

15.  
    1. Study the circuit shown below.
                                                   
       State and explain what happens to the identical lamps X and Y in the circuit shown when
       1. Switch S₂ only is closed (2mks)
       2. Switches S₁ and S₂ are closed (2mks)
    2. Graph A shows how potential difference across a battery varies with the current supplied.
       Graph B shows how the current in a filament lamp varies with potential difference across it.
       
       1. Use graph A to determine
          1. e.m.f of the battery (1mk)
          2. The internal resistance of the battery given V = -Ir+E (3mks)
          3. Calculate the resistance of the filament lamp when current through it is 1.5A (2mks)
16.  
    1.  
       1. The following nuclear reaction is part of a radioactive series
          
          1. Name the radiation represented by r and s (1mk)
             r………
             s………
          2. Determine the number represented by x and y (1mk)
             x………
             y………
       2. The figure below shows the features of diffusion cloud chamber used for detecting radiations from radioactive sources.
          
          1. State the property of alcohol that makes it suitable for use in the chamber (1mk)
          2. What is the purpose of the solid CO₂ ? (1mk)
          3. Explain how the radiation from the radioactive source is detected in the chamber. (2mks)
          4. State one advantage of the cold chamber over a charged gold leaf electroscope when used as detectors of radiation (1mk)
    2. The graph below shows how the activity of a sample of the radioisotope technetium which is used extensively in medicine, varies with time.
       
       1. Use the graph to determine the half-life, T ½ of technetium (1mk)
       2. Hence calculate the decay constant for technetium given that where λ is the decay constant. (1mk)
       3. Determine the number of technetium atoms remaining in the sample after 24 hours (1mk)
17. The figure below shows the features of an X-ray tube
     
    1.  
       1. What is the purpose of the oil going in and out of the anode (1mk)
       2. State with reason the property of tungsten that makes it suitable as a target (1mk)
    2. An X-ray tube operates with a potential difference of 100kv and filament current is 20mA. Calculate ;
       1. The power transferred to the target of X-ray tube (2mks)
       2. The number of electrons hitting the target per second (2mks)
       3. The maximum energy of X-ray produced (Take charge of an electron=1.6x10^-19C, mass of an electron =9.1x10^-31kg, f_max = 3 x 10¹⁹ Hz)             (2mks)
    3. The diagram shows monochromatic radiation falling on a photocell connected to a circuit
                          
       The incident radiation has a wavelength of 2.15x10^-7m. The metal surface of the photocell has a work function of 2.26 eV
       1. Calculate the energy in eV of a proton of the incident radiation (Take speed of  light C=3.0x10⁸ms^-1, Planck’s constant, h = 6.63x10^-34JS and electronic charge, e = 1.6x10^-19C) (3mks)
       2. What is the maximum kinetic energy of the emitted electrons (2mks)
       3. Write down the value of the stopping potential (1mk)
18.  
    1. State Lenz’s law of electro-magnetic induction (1mk)
    2. In the figure below, the bar magnet is moved out of the coil
                               
       1. If the current, I is induced in the coil in the direction shown, what is the polarity of x of the magnet? (1mk)
       2. Explain briefly the source of electrical energy in the circuit (1mk)
       3. A hydro-electric power station produces 500KW at a voltage of 10KV. The voltage is then stepped up to 150KV and the power is transmitted through cables of resistance 200Ω to a stepdown transformer in a sub-station. Assuming that both transformers are 100% efficient. Calculate;
          1. The current produced by the generator (2mks)
          2. The current that flows through the transmission cables (2mks)
          3. The voltage drop across the transmission cables (2mks)
       4. The power loss during transmission (2mks)
       5. The power that reaches the sub-station (2mks)
19.  
    1. The following graph shows the variation of image distance, v, with magnification, for a converging lens
       
       
       Using the graph and the equation  ^v/_f = M + 1 determine:
       1. The object position when the image position is 45 cm (2mks)
       2. The focal length of the lens (2mks)
       3. The power of the lens (2mks)
    2. The following figure shows an eye defect
        
       Name the defect and illustrate on the same diagram how the defect could be corrected. (2mks)

MARKING SCHEME.

SECTION A   (25 MARKS) 

Answer ALL the questions in this section in the spaces provided 

1. Two plane mirrors are inclined at an angle of 120° to each other such that their reflecting surfaces face each other. An object pins stands midway between the mirrors. Draw a ray diagram to show all the images (3mrks)
                                                            
   ✓ Correct position of two images
   ✓ Correct rays for image1
   ✓ Correct rays for image 2
2. State two conditions necessary for the occurrence of an annular eclipse (2mks)  
   • Moon too small to hide the sun completely
   • Ring of sunlight shows round the edge of the moon
3. The figure below shows two parallel rays incident on a concave mirror. F is the focal point of the mirror.
                                          
   • reffected rays (real) with arrows.
   • Image formed at the focal plane.
     Sketch on the same diagram the path of the rays after striking the mirror.   (2mks)
4. State the class of waves to which sound belongs   (1mk)
   • Longitudinal wave
5. Calculate the value of the critical angle C shown in the figure below   (2mks) 
              
   
   n₁ Sin C = n₂ Sin 90°
   Sin C =  n₂ sin 90°
                 n₁
   C = SIN^-1(^1.3/_1.5) = 60°
6. In the diagram below, two electroscopes A and B carry same type of charges as shown. The two are then connected with a copper wire as shown 
               
   State and explain the observations   (2mks)
   • The divergence of A drops slightly while B rises slightly. Both A and B will have qual divergence as they share changes equally.
7. The figure below shows a real image I formed by a convex lens
    
   On the same grid, construct a ray diagram to locate the position of the object   (2mks) 
8. State a property of electromagnetic wave on which the operation of a radar system is based (1mk)
   • The waves can be reflected.
9. The figure below shows an attempt to supply each of the three lamps L1,L2 and L3 with a switch 
                                   
   • Explain why this is a poor connection  (1mk) 
     
     • When switch is open, bulbs L₁, L₂ and L₃ will not light.
   • Redraw an adjacent diagram to show the best positioning for the switches  (1mk)
     •  Assessed by teacher
10. State one use of x-ray in medicine and one use in industry (2mks) 
    • X-ray photography to reveal fracture/killing cancer cells
    • Industries to detect flaws in metals.
11. Draw the magnetic field lines due to the configuration shown below  (1mk). 
                           
12. Sketch the current -voltage characteristic of a junction diode in a forward bias mode  (1mk)
               
    ✓ Well labelled 
13. The graph below represents values of /f and corresponding values of wavelength for waves transmitted in a certain medium 
    
    From the graph, determine the speed of the waves 
    G = 0·09 − 0·03 
             3 − 1
    =    0.06               
            2           →     C =  ¹/_g = ¹/_0.03      →
    G = 0.03                                                            = 33.33m/s     
14. State one causes of power loss in long distance transmission wires and how these loses can be minimized   (1mk)
    • High resistance in the cables, use thick conductors.
                            or
    • High current in the cables, stepping up voltage before transmission

                                                                                 SECTION B (55 MKS) 

                                                              Answer all questions in the spaces provided 

15.  
    1. Study the circuit shown below.
                                        
       State and explain what happens to the identical lamps X and Y in the circuit shown when
       1. Switch S₂ only is closed   (2mks) 
          • Bulbs X and Y light dimly beacuse they are connected in series offering a higher resistance to current
       2. Switches S₁ and S₂ are closed   (2mks)
          • Bulb X lights, brightly while Y does not because bulb Y is short circuted. V 
    2. Graph A shows how potential difference across a battery varies with the current supplied.
       Graph B shows how the current in a filament lamp varies with potential difference across it 
                       
       1.  Use graph A to determine
          1. e.m.f of the battery  (1mk)
             • 9.0V
          2. The internal resistance of the battery given V = -Ir+E   (3mks) 
             stope (g) =    (8 − 3)V    
                               (0.5 − 3.0) A
                          =      5V
                              −2·5A 
                           − r = −2Ω
                              r = 2Ω
          3. Calculate the resistance of the filament lamp when current through it is 1.5A (2mks) 
             Slope =  (4.2 − 1.0) V
                           (2.15 -0·9)A
             3.2
             1.25
             (Evidence of traingle to score 1st mark)
               Slope = resistance
                         = 2.56Ω
16.  
    1.  
       1. The following nuclear reaction is part of a radioactive series
           
          1. Name the radiation represented by r and s
             • r - beta  (½ mrk)
             • s - Alpha (½ mrk)
          2. Determine the number represented by x and y
             • x - 83 (½ mrk)
             • y - 82 (½ mrk)
       2. The figure below shows the features of diffusion cloud chamber used for detecting radiations from radioactive sources.
           
          1. State the property of alcohol that makes it suitable for use in the chamber
             • Volatile.
          2. What is the purpose of the solid CO₂?   (1mk) 
             • Lowers the temperature in the chamber until it is super saturated. 
          3. Explain how the radiation from the radioactive source is detected in the chamber. (2mks) 
             • Radition ionises air inside the chamber
             • Alcohol droplets from on the air ions produced by the radiation forming white tracks.
          4. State one advantage of the cold chamber over a charged gold leaf electroscope when used as detectors of radiation (1mk) 
             • Cold chamber can identify this type of radiation while a gold leaf electroscope cannot.
    2. The graph below shows how the activity of a sample of the radioisotope technetium which is used extensively in medicine, varies with time 
       
       1. Use the graph to determine the half-life, T 1⁄2 of technetium  (1mk)
          • 6 hours 
       2. Hence calculate the decay constant for technetium given that  where λ is the decay constant. (1mk) 
          6 = 0.6931 → λ =  0.6931 
                    λ                        6          = 0.1155
       3. Determine the number of technetium atoms remaining in the sample after 24 hours (1mk) 
          N = No(½)²⁴ = 8x10⁷ (½)²⁴ = 4.768 = 5 atoms
17. The figure below shows the features of an X-ray tube 
    
    1. 1. What is the purpose of the oil going in and out of the anode  (1mk)
          • It is used to cool the anode by conducting heat away.
       2. State with reason the property of tungsten that makes it suitable as a target  (1mk) 
          • high melting point 
    2. An X-ray tube operates with a potential difference of 100kv and filament current is 20mA. Calculate;
       1. The power transferred to the target of X-ray tube  (2mks) 
          P = IV = 20x 10⁻³ X 100000 = 2000W V 
       2. The number of electrons hitting the target per second 
          N =  I  =   20X10⁻³    =   1.25 x 10¹⁷ electrons
                 e       1.6x10^-19 
       3. The maximum energy of X-ray produced (Take charge of an electron=1.6x10^-19C, mass of an electron = 9.1x10^-31kg) (2mks)  Max range of X-rays = 3.0 x 10¹⁹ Hz
          E_max = hf_max = 6.63x10⁻³⁴ x 3x10⁹
                              = 19.89 x 10⁻¹⁵ = 1.989 x 10⁻¹⁴ J
    3. The diagram shows monochromatic radiation falling on a photocell connected to a circuit.
                                      
       The incident radiation has a wavelength o f 2.15x10^-7m. The metal surface of the photocell has a work function of 2.26 eV (3mks) 
       1. Calculate the energy in eV of a proton of the incident radiation (Take speed of light C = 3.0x10⁸ms^-1, Planck's constant, h = 6.63x10^-34JS and electronic charge, e = 1.6x10^-19C) \
          E = hc
                 λe
          = 6.63 x 10⁻³x 3x10⁸ 
             2.15 x 10⁻⁷ x 1.6 x 10⁻¹⁹ 
          = 5.782ev
       2. What is the maximum kinetic energy of the emitted electrons  (2mks) 
          K·E = 5.782 − 2.26 = 3.522ev.
                 = 3.522 x 16 x 10^-19 
                 = 5.635 X10^-19 Joules
       3. Write down the value of the stopping potential (1mk) 
          5.782 − 2·26 = 3.522ev
18.  
    1. State Lenz's law of electro-magnetic induction  (1mk)
       • The direction of the induced emf is such that the induced circuit it causes to flow produces a magnetic effect that oposses this change producing it.
    2. In the figure below, the bar magnet is moved out of the coil 
                                            
       1. If the current, I is induced in the coil in the direction shown, what is the polarity of x of the magnet?  (1mk)
          • North
       2. Explain briefly the source of electrical energy in the circuit  (1mk)
          • The magnetic flux cuts the coil inducing an emf in the coil hence electrical energy.
    3. A hydro-electric power station produces 500KW at a voltage of 10KV. The voltage is then stepped up to 150KV and the power is transmitted through cables of resistance 200Ω to a stepdown transformer in a sub-station. Assuming that both transformers are 100% efficient. Calculate;
       1. The current produced by the generator (2mks)   
          P = IV → 500000 = I x 10000
                     → I = 50A
       2. The current that flows through the transmission cables  (2mks) 
          V_s = Ip  →  I_s  =  V_pI_p   =  10000 x 50
          V_p    I_s                       V_s           150000      = 3.33A  (2d.p)  Atleast
       3. The voltage drop across the transmission cables
          V = IR
          3.333X 200 = 666.6V
       4. The power loss during transmission (2mks) 
          P = I²R =
          (3.33)² x 200 = 2217.78 W
       5. The power that reaches the sub-station (2mks)
          500000 − 2217.78  = 4975 782.22 W:
19.  
    1. The following graph shows the variation of image distance, v, with magnification, for a converging lens.
        
       
       Using the graph and the equation V = M +1 determine:
                                                              f  
       1. The object position when the image position is 45 cm  (2mks)
          M = V 
                 u
          → 3·5 = 45cm 
                          u
          u = 45
                3.5  = 12.86cm       (Look for evidence on the graph)
       2. The focal length of the lens (2mks) 
          V = mf + f(al − m = 0)
          V = f
          f = 10cm
       3. The power of the lens (2mks) 
          P = ¹/_f  = ¹/_0.1  = 10D
    2. The following figure shows an eye defect 
       
       ✓ Correct with arrows
       Name the defect and illustrate on the same diagram how the defect could be corrected. (2mks)
       • long sightedness (hypermetropic)