Physics Paper 2 Questions and Answers - Form 3 Mid Term 3 Exams 2023

INSTRUCTIONS TO CANDIDATES

• This paper consists of TWO sections: A and B.
• Answer ALL the questions in sections A and B in the spaces provided.
• ALL working MUST be clearly shown.
• Non-programmable silent electronic calculators and KNEC mathematical tables may be used.

SECTION A (25 MARKS)

Attempt ALL the questions in this section.

1. The figure below shows an object O placed in front of a plane mirror.
   
   On the same diagram, draw rays to locate the position of the image I as seen from the eye E. (2marks)
2. A circuit consists of a battery, metal wire, ammeter and a switch connected in series. The switch is closed and the ammeter reading noted. The metal wire is now heated.
   1. State the observations made on the ammeter reading. (1mark)
   2. Give one reason for the above observation made (1mark)
3. Figure 2 shows an incident ray normal to the surface BC of a right-angled glass prism ABC. The critical angle of the glass is 42°.
   
   Complete the diagram to show the path of the ray. (2marks)
4. The image formed by a convex mirror is virtual. State two other characteristics of image formed by the convex mirror.
   (2 Marks)
5.  
   1. State the basic law of magnetism. (1 mark)
   2. The figure below shows how magnets are stored in pairs with keepers at the ends.
      
      Explain how this method of storing helps in retaining magnetism longer. (2 marks)
6. The figure below shows a hack-saw blade clamped horizontally on a bench and the free end is made to vibrate about the rest position.
   
   The movement o → a → o → b → o→ a → o→ b takes 0.7second. Determine the frequency of vibration of the blade.
   (3 marks)
7. A current carrying conductor AB is in a magnetic field as shown in figure 1 below.
   
   1. Indicate the direction of the force F acting on the conductor. (1mark)
   2. State t factors that determine the direction of the force F. (2marks)
8.  
   1. Distinguish between a transverse and a longitudinal wave. (1 mark)
   2. Determine the frequency of the wave shown below. (2 marks)
      
9.  
   1. What is meant by the term “topping” as applied to a lead acid accumulator ? (1 mark)
   2. State two advantage of a lead acid accumulator over nickel-iron accumulator. (2 mark)
10. The figure below shows a sharp pin fixed on a cap of the electroscope. The electroscope is highly charged and then left for some time.
    
    Explain why the leaf collapses. (2 marks)
11. The figure below shows a positive charge near a plate carrying negative charge.
    
    Draw an electric field pattern between them (1 mark)

SECTION B (55 MARKS)

Attempt ALL the questions in this section.

12.  
    1. Define the refractive index of a substance . (1 mark)
    2. In an experiment to determine the refractive index in a liquid, the liquid was poured into a measuring cylinder. A pin was placed at the bottom of the cylinder and another pin was used to locate the apparent position of the first pin. The real and apparent depth were measured. The experiment was repeated with other values of real depth. The table below shows the results obtained.
       

       Real depth (cm)	5	10	15	20	25
       Apparent depth (cm)	3.3	6.7	10	13.3	16.7

       1. Plot the graph of real depth against apparent depth. (5 marks)\
       2. From the graph determine the refractive index of the liquid. (3 marks)
    3. The figure 5 shows a ray of light incident on a glass-air interface.
       
       Given that the refractive index of the glass is 1.6, determine angle θ. (3 marks)
13.  
    1. State Ohm's law. (2 mark)
    2. Study the circuit diagram (Fig 6) below and answer the questions that follow.
       
       1. Calculate the effective resistance of the circuit. (4marks)
       2. Find the total current in the circuit. (3 marks)
    3. The figure 7 below shows a low voltage lighting circuit.
       
                  Fig 7
       1. On the figure indicate with letter S a point in the circuit where a switch could be placed that would turn off lamp Y and Z at the same time but would leave lamps X still lit. (1 mark)
       2. The current in lamp Z is 3.0A, calculate the resistance of this lamp. (3 marks)
14. In figure 15 shown below. Two identical electroscopes A and B carry the same type of charges as shown. The two are then connected with a copper wire.
    
    
    1. State and explain the observations made. (2 marks)
    2. When a charged body P is brought close to the cap of a negatively charged electroscope the leaf of the electroscopes rises. State with reason the charge on the body P. (2 marks)
    3. Four capacitors were connected in a circuit as shown in figure 16 below. Determine the charge stored in the combination of the capacitors when the switch is closed. (4 marks)
       
    4. State two ways in the capacitance of a parallel plate capacitor can be increased. (2 marks)
15.  
    1. A person standing behind a wall hears a bell ringing although he cannot see the bell. What property of sound enables him to hear the sound? (1 mark)
    2. The figure below is a sketch of ripples caused by a vibrator in a ripple tank whose frequency is 50Hz.
       
       Using the above information, determine the speed of the wave motion. (3 marks)
    3. The speed of sound in air determined on a warm day is 330m/s. Explain any difference you would expect in the results if the measurement is done on a cold day. (2 marks)
    4. In an experiment to determine the speed of sound, an observer stood in front of a high wall at a distance of 80m. He clapped two boards together at such a rate that each clap coincided with the echo from the wall. A second observer noted a time of 9.5 seconds starting with first clap and ending with the 21st clap.
       1. Calculate the speed of sound under these conditions. (4 marks)
       2. Describe two probable source of error in this experiment. (2mark)
       3. State two way in which sound wave differ from light waves. (2 mark)

MARKING SCHEME

Section A (25 marks)

1. The figure below shows an object O placed in front of a plane mirror.
   2 diverging rays ✓¹  Position of the image
2.  
   1. The ammeter reading decreases✔
   2. The resistance of the metal increases with increase in temperature.✔
3.  
   
4.  
   • always upright
   • always smaller than oject / accept diminished
     reject: formed behind the mirror
5.  
   1. State the basic law of magnetism. (1 mark)
      • Unlike poles attract, like poles repel ✓¹
   2. The keepers become magnetized thus neutralizing ✓ the pole; this reduces repulsion at the poles ✓ thus helping in retention of magnetism.
6. One cycle = a → a = 4 spaces
   each space = 0.7 = 0.1 second
                           7
   T = 0.1 × 4 = 0.4 second ✓1
   f = 1/T
     =  1  = 2.5Hz    ✓1
        0.4
7. A current carrying conductor AB is in a magnetic field as shown in figure 1 below.
   1.  
      (1mk)
   2.  
      • Direction of magnetic field. ✓
      • Direction of the current (2mk)
8.  
   1. Distinguish between a transverse and a longitudinal wave. (1 mark)
      

      Transverse	Longitudinal wave
      Displacement of particles in the wave is perpendicular to the direction of wave motion.	Displacement of particles in the wave is parallel to the direction of wave motion.
      Requires no medium for propagation.	Requires a material medium for propagation.
      Can be mechanical or electromagnetic in nature.	Purely mechanical wave.

      Any 1 combination
   2. f = ¹/_T = 2(s)
      Hene f = ¹/₂ = 0.5Hz
9.  
   1. Topping is adding distilled water in the lead acid accumulator so that the plates are submerged 
   2. It has a higher e.m.f compared to nickel iron type. It is less expensive than nickel iron type any one ✓
10. Charges concentrate1 on the sharp end of the pin resulting into net reduction of charges on the leaf making it collapse.
11.  
    

Section B (55 Marks)

12.  
    1. This is the ratio of sine of the angle of incidence to the sine of the angle of refraction.
       OR
       n = Sin i  
             Sin r
    2.  
       1. for the graph check
          scale   1 mk
          line      1 mk
          ploting 2 mks
          axes    1 mk
                      5 mks
       2. M = Δy  
                 Δx
             = 15 − 6 = 9   
                10 − 4     6
             = 1.5 ± 0.1        3 marks
    3. n =   1      1.6 =    1     
             sin θ            Sin θ
       1.6 Sin θ = 1
       Sin θ =  1   = 0.625
                   1.6 
       Sin⁻¹ = 0.625 = 38.68%
13.  
    1. current through conductor is directly proportional to the applied voltage provided temperature and other physical conditions are kept constant.
    2.  
       1. Parallel resistance  = 6 × 5 = 2.73Ω
                                             6 + 5
          Parallel resistance = 4 × 2 = 1.33Ω
                                            4 + 2
          Series resistance = 3.00✓
          Effective resistance
          = 2.73 + 1.33 + 3.00
          = 7.06✓✓1 3 marks
       2. I = ^V/_R = ⁶/_7.06 = 0.84A
    3.  
       1.  
          
          R = ^V/_I 
       2. = ¹²/₃ = 4Ω
          M = Δy  
                  Δx
          =   = 15 − 6 = 9   
                10 − 4     6
             = 1.5 ± 0.1
14.  
    1.  
       • Leaf in A decreases in divergence
       • B increases in divergence electrons flow from B to A ✓1
    2. P is negatively charged ✓1 The body repels more negative charge from the cap to the leaf. ✓1
    3. CT = 2 × 2 + 3 × 3 = 2.5μF
                2 + 2    3 + 3
       Q = CV
           = 2.5 × 10⁻⁶ × 3 = 7.5 × 10⁻⁶C
    4.  
       • Decreasing distance between plates.
       • Increase area of overlap of the plates
       • using a dielectric with a higher dielectric constant. (any two✓1 ✓1 )
15.  
    1. Diffraction ✓1
    2. l = 24 = 8cm
             3
       v = f✓
       = 50 × ⁸/₁₀₀ ✓1
         = 4 m/s ✓1
       
    3. The speed will be lower because of low temperature ✓1
    4.  
       1. V = n × 2d
             = 20 × 2 × 80
                       9.5
             = 336.8 m/s
       2. The time for the 20 claps might not be accurate. ✓1
       3. Requires a material medium to travel through. ✓