Physics Paper 2 Questions and Answers - Form 3 End Term 3 2021

END OF TERM 3
FORM 3 PHYSICS PP2

SECTION A : (25 MARKS)

Answer all the questions in this section in the spaces provided.

1. Figure 1 below shows an object infront of plane mirror.
   Figure 1     
   Sketch image of object using mirror shown. (1mk)
2. Figure 2 below shows an object infront of concave mirror and it’s image.
   Figure 2
   Locate position of its principal focus. (2mks)
3. State the use of Manganese (IV) oxide in dry cell. (1mk)
4. Use figure 3 below to answer following questions.
   figure 3
   Determine
   1. Total resistance. (3mks)
   2. Potential difference across 4Ω resistor. (3mks)
5. Figure 4 shows conductor carrying current in magnetic field and moves in direction shown.
   Figure 4
   Identify polarities X and Y. (2mks)
6. A man standing between two parallel walls fires a gun. He hears an echo after 1.5 seconds and another one after 2.5 seconds and yet another one after 4 seconds. Determine the separation of the walls. (Take velocity of sound 340 m/s)
7. A student shouts and hears an echo after 0.6 seconds. If the velocity of sound is 330m/s. Calculate the distance between student and reflecting surface. (3mks)
8. Figure 6 shows water waves moving towards barrier. Show the emergence of the reflected waves
   Figure 6
9.  
   1. Define refractive index. (1mk)
   2. The critical angle of a material is 43.2⁰. Determine the refractive index of that material. (2mks)
   3. A battery of emf E drives a current of 0.25A when connected to 5.5W resistor. When the 5.5W resistor is replaced with 2.5W resistor, the current flowing becomes 0.5A. Find the emf E and the internal resistance r of the battery. (3 marks)
10. Define the term sulphation as applied to lead acid cells. (1 mark)

SECTION: B(55MARKS)

ANSWER ALL QUESTIONS IN THIS SECTION

11.  
    1. An uncharged metal rod brought close but not touching the cap of a charged electroscope causes a decrease in the divergence of the leaf. Explain the observation. (1mark)
    2. In experiment to investigate factors affecting capacitance of a capacitor, a student increased the area of the plates and decreased the separation of the plates. Explain the effect on the capacitance when
       1. the area of plates increased (1 mark)
       2. the distance of the separation of the plates decreased (1 mark)
    3. Figure 7 illustrates a method of charging a metal sphere.
       Fig. 7.
       1. Name the method of charging shown in fig 8.(1mar(ii) Indicate the final charge on the sphere in fig 8. (1 mark)
    4. Figure 9 shows an arrangement of capacitors connected to a 10V d.c supply.
       
       Determine
       1. the combined capacitance (2 marks)
       2. the total charge in the circuit (1 mark)
       3. the total energy stored in the circuit. (2marks)
12.  
    1. Distinguish between e.mf. and terminal voltage of a battery. (2 marks)
    2. The graph in figure 8 shows the variation of potential difference V against current I for a cell when current is drawn from it.
       
       From the graph determine
       1. The e.m.f of the cell. (2 marks)
       2. The internal resistance of the cell. (4marks)
    3. On the space provided below, draw a circuit that could be used to obtain the results represented by the graph. (2 marks)
13.    
    1. Figure 9 is an illustration of a wave pattern.
       
       1. State with reason the type of wave shown. (2 marks)
       2. Determine the wavelength of the wave. (1 mark)
       3. Calculate the frequency of the wave given that the speed of the wave is 9m/s. (3 marks)
    2. Figure 10 show s monochromatic source of light L behind a barrier with a single slit S placedbehind another barrier with two identical slits S1 and S2. A screen PQ is placed in position as shown.
       
       1. Explain what is observed on screen PQ. (2 marks)
       2. What is the significance of S1 and S2 ? (1 mark)
14. Figure 11 shows an electromagnetic relay being used to switch an electric motor on and off. The electromagnet consists of a coil of wire wrapped around a core. The motor in figure is switched off.
    
    1. Suggest suitable material for the core. (1mark)
    2. What happens to the core when switch S is closed? (2marks)
    3. Why do the contacts A and B close when the switch S is closed. (2marks)
    4. When the switch S is opened, what will happen to;
       1. The core (1mark)
       2. Soft iron armature. (1mark)
    5. Give one other application of an electromagnet. (1mark)
    6. State two ways in which an electromagnet could be made more powerful. (2marks)
15. Figure 12 below shows a narrow beam of white light onto a glass prism.
    
    1. What is the name of the phenomenon represented in the diagram? (1mk)
    2. Name the colour at X and Y. Give a reason. (3mks)
    3. What is the purpose of the slit? (1mk)
16. The figure 4 shows a circuit with a coil used to warm oil in a beaker.
    
    
    1. State the Ohm’s Law. (1mk)
    2.    
       1. Explain how heat is produced in the coil. (2mks)
       2. Given that the reading of the ammeter is 2.5A, determine the resistance of the coil. (3mks)
       3. How much heat is produced in the coil in a minute? (3mks)
       4. Give two changes that can be made in the set-up in order to produce more heat per minute. (2mks)
       5. How much heat is produced in the coil in a minute? (3marks)

MARKING SCHEME

SECTION A

1.   
   
2.   
   rays with arrowsposition of F
3. Depolarizer
4.    
   1. 4 + 3 = 7Ω
        1  +   1  =  12  
       7        5      35
      = 35/12= 2.916Ω
   2. I = 12 + 12 = 144 = 4.1143A
            35             35
      C(4Ω ) = 5/12 x 4.1143 x 4 = 6.857V
5.    
   • X - North
   • Y - South
6.    
   
   Alternative: 2d = V
                      t
   Time for second echo = 5/2 = 2.5 seconds
    1.5 + 2.5 = 40 seconds
   D= 5 x t = 330 x 4 = 1320m
7.    
   1. S = vt =330 x 0.6 = 99m
   2.    
      1. E = IR + Ir
         E = 0.25 × 5.5 + 0.25 r
         E = 0.5 × 2.5+ 0.5 × 5
         E = 1.35 + 0.25r
         E = 1.25 + 0.5 r
         0 = 0.10 - 0.25 r
         0.25r = 0.10
          0.1   = 0.4Ω
         0.25
         E= 1.35 + 0.25 x 0.4
           = 1.45
8.   
   
9.    
   1. Ration of sine of angle of incidence to sine of angle of refraction for a given pair of media.
   2. n =   1   =    1              = 1.461
           Sin C     Sin C 43.2⁰ 
10. Hardening of lead sulphate on the lead plates 

SECTION B 55 MARKS

11.  
    1. A metal rod is a good conductor of charge hence the electroscope 
    2.  
       1. Increase 
       2. Increases 
    3.  
       1. Induction 
       2. Electrons from the earth to the sphere  to neutralize the repelled positive charges 
       3. Negative charges.
    4.  
       1. Series = (3 x 3)/(3+2) = 9/6 = 1.5μF
          in parallel with 2μF
          CT = 1.5 + 2 = 3.5μF
          In series with 1μF
          CT = (3.5 x 1)/(3.5+1) = 3.5μF/4.5μF
          = 0.78μF
          = 7.8 x 10^-7F 
       2. 7.8 x 10-7 x 10 
          = 7.8 x 10^-6 C
       3. E = ½CV²
          = ½ x 7.8 x 10^-6 x 10 
          = 3.9 x 10^-5J 
12.  
    1. E.m.f is the p.d. across the battery in the ü1 open circuit while terminal voltage is the p.d. across the cell is a closed circuit.
    2.  
       1. E.m.f = 1.625V ü1 (show unit)
       2.  E = IR + Ir
          V = E - Ir
          V = Ir + Slope =
          -r = 1.5 - 1.0   =    0.5   = 0.78
                 0.16 - 0.8     -0.64
          r= 0.78Ω
13.  
    1.  
       1. Transverse wave 
          • The particles vibrate at right angle to the direction of motion of the wave 
       2. The wavelength = 50cm or 0.5m 
       3.  v = f 
            f =   9  
                  0.5
          = 18Hz
    2.  
       1.  
          • Bright and dark fringes are formed 
          • Bright fringes are formed where constructive interference occurs while dark fringes are formed were destructive interference occurs 
       2. Produce coherent sources of light.
14. 1. Soft iron
    2. The current flows through the solenoid; it is magnetized and attracts the soft iron armature.;
    3. The magnetized core attracts the soft iron armature. The pivot armature pushes the springy metal strip which joins contact B and A.;;
    4.  
       1. The core (1mark)
          • It loses its magnetism;
       2. Soft iron armature. (1mark)
          Soft iron goes back to its original position thus switching off the current in the circuit.;
    5. Give one other application of an electromagnet. (1mark)
       • Electric bell, telephone receiver, moving coil loudspeaker and circuit breaker.
    6. State two ways in which an electromagnet could be made more powerful. (2marks)
       • Using a soft iron core, increasing the current and
       • Increasing the number of turns;;
15.  
    1.  
       • Dispersion of light.
       • X – Red
         Y – Violet
         
         • Red has the lowest frequency/longest wavelength hence least deviated while violet has the highest frequency/shortest wavelength hence most deviated.
       • Act as point source of light.
16.  
    1. The current flowing through the conductor is directly proportional to the potential difference across its ends provided temperature and other physical conditions are kept constant.
    2.  
       1. When the switch is closed the current flows through the coil which offer resistance hence dissipating heat.
       2. V = IR 
          R= V= 12  = 4.8Ω
               I     25
              
       3. Heat = Vlt 
          = 12 x 2.5 x 60 
          = 1800J 
       4.  
          • Increasing the number of coils. 
          • Increasing the current. 
    3. The readings will decrease because the resistance is decreased. ¹