Physics Paper 2 Questions and Answers - Form 3 End Term 3 2022 Exams

QUESTIONS

SECTION A (25 MKS) ANSWER ALL

1. State one similarity between an alkaline battery and lead acid battery. (1mark)
2. The fig 1 below shows a ray of light incident on a mirror.
   
   Fig 1
   Determine the angle of reflection when the mirror is rotated 100 anticlockwise. (2marks)
3. State the condition under which the potential difference across the terminal of a cell is equal to its e.m.f. (1mark)
4. The fig 2 below shows a displacement – distance graph of a wave profile.
   
   Fig 2.
   1. State the amplitude of the wave. (1mark)
   2. Given that the period of the wave is 0.255, determine the velocity of the wave. (2marks)
5. State the property of light applied in transmitting light signals in optical fibres. (1mark)
6. The figure 3 below shows two bar magnets and plotting compass.
   
   Figure 3
   Draw the magnetic field pattern round the bar magnets indicating the polarity of each. (2marks)
7. 7. A soldier standing some distance from a wall blows a whistle and hears its echo 1.8seconds later. How far is the wall from the soldier ? (Speed of sound in air = 330m/s) (3marks)
8. The fig. 4 below shows the conductivity wires A and B passing through a horizontal piece of card board
   
   
   1. Sketch the resultant magnetic field pattern when the currents of high magnitudes are flowing on both wires as shown. (1mark)
   2. What is the resulting effect of the field on the wires at the loose ends? (1mark)
   3. If the current in B were to be reversed , state how the resulting effect would affect the wire conductors. (1mark)
9. The fig.5 below shows the image, I formed by a concave mirror. Locate using ray diagrams the position of the object. (2 Marks)
   
   Figure 5.
10. A 10μF capacitor is charged by 100v supply and then connected across an uncharged 20μF capacitor.
    Calculate the final p.d on each capacitor. (3marks)
11. Other than temperature, state any other factor that affect the resistance of an ohmic conductor. (1mark)
12. A car battery requires topping up with distilled water occasionally. Explain why this is necessary and why distilled water is used. (2marks)
13. Two similar razor blades are placed one on a wooden block and the other on a soft iron block as shown in figure 6 below.
    
    It was observed that the razor blade on the wooden block was attracted to the magnet while the one on the soft iron block was not. Explain the observation. (2marks)

SECTION B (55MKS). ANSWER ALL QUESTIONS

14.                          
    1. Draw the electric field pattern in the fig.7 below. (2marks)
       
       Figure 7
    2. Fig. 8 shows a system of capacitor connected to R 100v supply.
       
       Determine:
       1. the effective capacitance of the circuit. (3marks)
       2. the charge through the 6μf capacitor. (3marks)
       3. the p.d across the 8μf capacitor. (5marks)
    3. State the factors that affect the capacitance of a parallel plate capacitor. (2marks)
15. The fig. below shows an object placed in front of a concave mirror of focal length 10cm. C is the center of curvature.
    
    
    1. On the same fig. draw a ray diagram showing the position of the image. (3marks)
    2. Use the ray diagram in (a) above to determine:
       1. the image distance. (1mark)
       2. magnification. (1mark)
       3. State two characteristics of the image. (2marks)
    3. A building standing 20M from a pinhole camera produces on the screen of the camera an image 2.5cm high, 5cm behind the pinhole. Determine the actual height of the building. (3marks)
16.                      
    1. Name the property of light that shows it is a transverse wave. (1mark)
    2. State a characteristic of sound, which is determined by a overtone. (1mark)
    3. Distinguish between stationary and progressive waves. (1mark)
    4. State the condition for a minimum to occur in an interference pattern. (1mark)
    5. State two ways by which the frequency of a note produced by a given guitar may be increased. (2marks)
    6. In an experiment using ripple tank the frequency, f, of the electric pulse generator was reduced to one third of its value. How does the new wavelength compare with the initial wavelength? Explain your answer. (3marks)
    7. State one observable change on water waves when passed from deep to shallow water. (1mark)
17.                      
    1. State the Snell’s law. (1mark)
    2. A coin is placed beneath a transparent block of thickness 10cm and refractive index 1.56. Calculate the vertical displacement of the coin. (2marks)
    3. The speed of free light in a prism is 1.94x 10⁸ m/s.
       1. Determine the refractive index of the prism material.(speed of light in air = 3.0 x10⁸ m/s) (2marks)
       2. Determine the critical angle of the prism material. (2marks)
    4. State the advantage of using optical fibre in communication. (2marks)
    5. The refractive indices of water and floss are 3/2 and 4/3 respectively. Find the value of θ in the fig. below. (2marks)
       
18.                        
    1. Figure below shows a graph of potential difference .v(volts) against current , I (amperes) for a certain device.
       
       From the graph:
       1. State with a reason whether or not the device obeys ohm’s law. (2marks)
       2. determine the resistance of the device at ;
          1. I=1.5 A (2marks)
          2. I= 3.5 A (2marks)
       3. From the results obtained in (ii) state how the resistance of the device varies as the current increases. (1mark)
       4. State the cause of this variation in resistance. (1mark)
    2. Three identical dry cells each of e.m.f 1.6v are connected in series to a resistor of 11.4Ω. a current of 0.32a flows in the circuit. Determine:
       1. the total e.m.f of the cells. (1mark)
       2. the internal resistance of each cell. (2marks)

MARKING SCHEME

1. Both batteries are chargeable. 
2. Initial angle of reflection =90º -48º
   =42º =initial angle of incidence
   New angle of incidence =90º –(48º - 10º) 
   =52º
   New angle of reflection =52º
3. In an open circuit. 
4.                          
   1. Amplitude =0.2m 
   2. Wave length λ=0.4m
      v=f λ
      =1/0.25x0.4
      v= 1.6 m/s 
5. Total internal reflection.
6.                            
   
   - Naming polarities
   - Field pattern
7. Speed=2d/t
   d=speed x time
                2
   = 330 x 1.8 m
             2
   =297 m
8.                
   1.                          
      
      
   2. Wires attract each other.
   3. Wires would repel each other.
9.                                
   
   - Any 2 rays draw.
   - Object between c and f.
10. Q= CV =10x100
    =1000 μFV
    CT =C1 +C2
    =20 +10
    =30μF.
    V=Q/CT = 1000 μFV
                         30 μF
    =33.33 V 
11. - Length of the material
    -Nature of the material                any 1
    -Cross-sectional area.
12. Evaporation on the cell reaction cause hrs of water.
    Distilled water is used because it does not introduce impurities to the cell.
13. - Magnetism was induced on soft iron.
    -No magnetism was induced on wooden block since it is non magnetic.
14.                              
    1.                                          
       
    2.                  
       1. Capacitance in parallel =4 +8 =12 μF.
          Capacitance in series ,1/CT =1/12+1/6=3/12
          CT =12/3= 4/μF
       2.  Q =CT V
          =4x100 μC
          =400Μc or =4x10-4C
       3. P.d across 6μc capacitor, V1 =Q/C
          =400/6
          =66.67V
          P.d across 8/μ f capacitor ,= 100-66.67
          =33.33V
    3. Area of overlap
       Distance between plates (2x1=2mks for any two correct factors)
       type of dielectric
15.                    
    1. GRAPH
       
    2.                    
       1. Image distance =7.5cm
       2. Magnification m= 7.5/5 =1.5
       3. Virtual
          Enlarged 2x1=2m. any two correct
          upright
    3. M=hi/h0 =v/u
       2.5cm/h0 =5cm/200cm
       ho =2.5cmx200 cm
                      5
       =1000cm
       =10m
16.                    
    1. Polarization.
    2. Quality of sound.
    3. Progressive wave –wave profile moves along with the speed of the wave.
       -Stationary wave –wave profile appears static.
       OR
       Progressive –Energy translation in the direction of the wave travels.
       Stationary wave –No translation of energy but energy associated in the wave.
    4. The two waves must be completely out of phase with one another.
    5. Increasing the tension.
       -Reducing the length.
    6. V=f λ
       λ1 is initial length
       λ2 is final length
       Then , V =f λ1 and V=f λ2
                          3
       Since V is constant
       f λ1 =f λ2
               3
       λ1 =3λ1 wave length increases 3 times.
    7. Speed reduces or wavelength decreases. any
17.                        
    1. The ratio of the fire of angle of incidence to the fire of the angle of refraction is constant.
    2. ∫ = Real depth
          Apparent depth
       1.56=10/x
       1.56x=10
       x=10/1.56
       =6.410
       Vertical displacement =10 -6.410 =3.59cm.
    3.                  
       1. ∫ = velocity of light in vacuum
          velocity of light in medium
          3.0 x 108
          1.94x 108
          =1.546
       2. 1/sin c = 1.546
          sin c =1/1.546
          c=40.300
    4. -Minimal energy losses due to total internal reflection .
       - Large quantity of data can be converted per unit time
       -Its flexible.
       =2/3x 4/3=8/9
       =fin 30/finθ =8/9
       finθ = fin 30x 9/8
       =0.5x 9/8=0.5625
       =θ=34.230
18.                      
    1.                  
       1. -Does not obey ohm’s law.
          - Current is not directly proportional to voltage.
          - The graph is not linear.
       2.                                      
          1. at I =1.5 A ,R =gradient of tangent at I
             9.2 -4.8
             3.6 -0.1
             =1.26Ω
          2.  At I =3.5A ,R= gradient of tangent at I
             9.4-7.2
             5.4 -1.5
             =0.56Ω
          3.  As current increases , resistance decreases .
          4. Change in temperature.
    2.                      
       1. E =1.6 +1.6+1.6
          =4.8V
       2. Let r be the combined internal resistance .
          E= I (R+r)
          4.8=0.32(11.4+r)
          =3.648 +0.32r
          R =3.6Ω
          Internal resistance of each cell =3.6/3=1.2Ω