Physics Paper 2 Questions and Answers - Mokasa II Joint Mock Exams 2023

Instructions to candidates

• This paper consists of two sections A and B
• Mathematical tables and electronic calculators may be used
• Use the following;
  Velocity of light c = 3.0× 10⁸ms^-1
  Mass of an electron me = 9.1× 10^-31kg
  Planks constant = 6.63× 10^-34Js

SECTION A (25MARKS)

1. The diagram below shows two rays from an object O. Complete the ray diagram to show the image I position (2marks)
   
2.  An object 0.5m high is placed 4m in front of a pinhole camera and forms an image 2.5 cm tall. Determine the length of the camera (2marks)
3. The diagram (figure 2) below shows a neutral leaf electroscope
   
   Given a dry glass rod and silk cloth .Describe briefly how you would charge the electroscope negatively by induction (3marks)
4. A form one student connected the circuit as shown in the figure 3 below with two identical bulbs B₁ and B₂ to an emf source.
   
   1. State and explain the observation made when both the switches S1 and S2 are closed (2marks)
   2. If the emf of the source is 3.0V and of negligible internal resistance and the ammeter reads 0.3A.when both the switches S₁ and S₂ are closed .Determine the resistance of each bulb (2marks)
5. One of the maintenance practices of accumulators is to maintain the level of the electrolyte above plates is by regularly topping up with distilled water and not acid. Explain why acid is not used (2marks) 
6. Figure 4 below shows an image I formed by a convex mirror of an object placed in front of it.
   
   Complete the ray diagram to locate the position of the object (2marks) 
7. In an ac generator the induced emf can be increased by increasing the speed of rotation. State two other adjustments that can be done to give the same effect. (2marks)
8. The diagram below shows a decay series in a nuclear equation where a parent nuclide X decayed to form a daughter nuclide plus radiation Z.
   
   State the values of B and identify the type of radiation
   
   1. B………………………………………………… (1mark)
   2. Radiation type…………………………….. (1mark)
9.  
   1. Define photoelectric effect (1mark)
   2. What do you understand by the term threshold wavelength as used in photoelectric effect (1mark) 
10. The figure 5 below shows a wave form of a displacement –time graph of a certain wave.
    
    Determine the frequency of the wave (2marks)
11. A transmitter of ultrasound sends it to the bed of the sea. If the depth of the ocean is1.4km and the echo is received after 0.2seconds.Determine the speed of sound in water (2marks)

SECTION B (55MARKS)

12.  
    1. Define the term radius of curvature of a lens (1mark)
    2. When a lamp is placed 10cm from a convex lens of focal length 20cm it produces an image on the same side as the object.
       1. State and explain one practical application of the set up arranged this way (2marks)
       2. Determine the position of the image of the lamp (2marks) 
    3. In an experiment to determine the relationship between real and apparent depth of a coin placed at the bottom of a beaker .Several values of the real depth and the apparent depth when viewed from above were recorded
       
       1. In the axes provided below sketch a graph of apparent depth against real depth (1mark)
          
       2. Explain how the graph can be used to determine the refractive index of water (1mark)
13.  
    1. Figure 7 below shows a pattern of water waves incident onto a concave reflector as shown
       
       1. Complete the diagram to show the pattern of waves after reflection (2marks)
       2. On the diagram indicate clearly the principal focus F of the concave reflector (1mark)
    2. The figure 8 below shows a section of a swimming pool with deep section at X and shallow end at Y as viewed from the side
       
       The vibrator is connected to electric pulse vibrator
       1. Identify the type of waves generated by vibrator on the water surface (1mark)
       2. On the surface of water as viewed from above as shown below. Sketch the refracted waves as they progress from X to Y (1marks)
          
       3. A radio waves transmitted by CNN station has a frequency of 60MHZ .If the speed of the waves is 3.0 × 10⁸ms^-1 .Determine the wave length of CNN waves (2marks)
14.  
    1. Figure 10 below represents two parallel plates capacitor separated by a distance d mm
       
       Suggest two adjustments that can be made so as to reduce the effective capacitance (2marks)
    2. The figure below shows an arrangement of capacitors of 3μF, 10μF and 5μF connected to a 10V emf source supply as shown.
       
       1. Determine the effective capacitance of the circuit (2marks) 
       2. The charge stored across 5μF capacitor (2marks) 
       3. The energy stored in 10μF capacitor (2marks)
15. Figure 12 below shows a beam of cathode rays entering a space between two charged plates A and B.
    
    1. On the same diagram sketch the path followed by the beam of the cathode rays between the plates into the space beyond the plates (1mark)
    2. The picture below shows the image of human hand made using x-rays
       
       State and explain the property of the X –rays that help in making the above image of the hand (2marks)
    3. An x-ray machine operates at a potential of 80Kv only 0.5% of the electron energy is converted to x–rays while the rest is converted to heat at the anode at the rate of 99.5Js^-1
       Determine;
       1. The tube current (3marks)
       2. Average velocity of the electron hitting the target (2marks)
       3. Minimum wavelength of the x- rays (2marks)
16.  
    1. Explain why it is not safe to have a switch inside the walls of a bathroom (1mark)
    2. State two ways of minimizing power loss in the transmission of power (2marks)
    3. State one condition for an electrical appliance to be connected with two pin plug for connecting it to power socket. (1mark)
    4. A cable of resistance 20Ω is used to connect a house for domestic power consumption to supply 14.4kw at 240V.Calculate;
       1. The current in the cable (2marks) 
       2. The power loss in the cable (2marks)
    5. Figure 14 below shows a three pin plug connected to mains supply with the conventional colours as indicated
       
       Identify any two mistakes in the wiring (2marks)
17. Silicon is a pure semiconductor in group four of the periodic table
    1. Explain how silicon can be changed into
       1. p-type semiconductor (1mark)
       2. n-type semiconductor (1mark)
       3. What is meant by the term p-n junction? (2marks)
    2. The circuit in figure 14 below shows diodes and bulbs which are connected to a dc power supply
       
       1. State and explain which bulbs will light when the switch S is closed (2marks)
       2. Explain why increase in temperature increases the conductivity of a pure semiconductor (2marks)
18. The cells in the figure below have each 2.0V and negligible internal resistance
    
    Determine;
    1. Total current in the circuit (2marks)
    2. The voltmeter reading (1marks)
    3. Current through 20Ω resistor (2marks)

MARKING SCHEME

1.  
   
2. v/u = I/o ⇒ v = u × 1
                              0
                        = 4m × 2.5cm = 0.2m
                                  50cm
3.  
   • Charge the glass rod positively by rubbing with a piece of silk cloth
   • Place it close to cap with out touching
   • Earth the cap and remove the earth on the rod.
4.  
   1.  
      • Only B lights
      • B₂ is short circuted by switch S₂
   2. R = ^V/_l = 3.0v = 10Ω
                     0.3A
5.  
   • When in use only water evaporates making electrolyte more concentrated.
   • Hence need to dilute only with distilled water.
6.  
   
7.  
   • increasing the strength of the Magnetic fiend
   • Winding turns on soft iron core
   • Increasing number of turns of the coil
8.  
   1. B  −1
   2.  Radiation type B - Beta
9.  
   1. Emmission of elections from a metal surface when a radiation of sufficient frequency is incident onto the surface.
   2. The maximum wavelength of a radiation incident onto a metal surface beyond which no photoelectric emmission will occur. 
10. T = 0.6s ⇒ f = ¹/_T = ¹/_0.6 = 1.667HZ
11. V = Distance = 1400M = 1400ms⁻¹
              Time         0.1s 
12.  
    1. Radius of a circle forming the arc of the mirror
    2.  
       1.  
          • Magnifying glass (simple microscope)
          • Image formed is virtual erect and magnified making it larger than object.
       2. ¹/_f = ¹/_u + ¹/_v 
          ¹/₂₀ = ¹/₁₀ + ¹/_v 
          ¹/_v = ¹/₂₀ − ¹/₁₀ 
          ¹/_v = −¹/₂₀ 
          V = − 20cm
    3.  
       1.  
          
       2. Refractive index n = Inverse of the gradient
13.  
    1.  
       1.  
          
    2.  
       1. Parallel waves
       2.  
          
       3. λ = ^e/_f
          λ = 3.0 × 10⁸ms⁻¹ = 5m
                   6.0 × 10⁷    
14.  
    1.  
       • Rotated one sideways to reduce the overlap area.
       • Pull the plates apart to increase d mm
    2.  
       1. (3×5) + 10 = 11.875μF
          (3+5)
       2. Q = 1.875 × 10⁻⁶F × 10v
              = 1.875 × 10⁻⁵C
       3. E = ¹/₂CV²
             = ¹/₂ × 10 × 10⁻⁶F × 10V × 10V
            = 5 × 10⁻⁴J
15.  
    1.  
       
    2.  
       • High penetrating power
       • X-rays pass throguh different tissues at different rates causing different reaction on photographic films forming clear outline of the tissues.
    3.  
       1. I = 99.5% = 0.995
          P_input = P_output   =  99.5  = 100w
                             1       0.995
          Pinput = I.V
          I =   100   = 1.25 × 10⁻³A
                80000 = 1.25mA
       2.  
          
       3.  hc    = e
          λ_min   
          λ_min = hc   
                     ev
          λ_min = (6.63 × 10⁻³⁴ ×3 × 10⁸ )
                       1.6 × 10⁻¹⁹ × 80000
          λ_min = 1.554 × 10⁻¹¹m
16.  
    1. Avoid water splash into the switch causing electrocution of a person standing in the water.
    2.  
       • High voltage transmission
       • Using thick aluminium conductors
    3. Casing made of insulator
    4.  
       1. I = ^p/_v = 14400w = 60A
                          240v
       2. Powerloss = I²R
                           = (60 × 60 × 20) = 72,000W
    5.  
       • Fuse on neutral instead nof live
       • Earth cable red instead of green
       • Green cable connected to live.
17.  
    1.  
       1. Dopine intrinsic semiconductor with trivalent atoms  (group three)
       2. Dopine intrinsic semiconductor with pentavalent atoms (Group five)
       3. Intrinsic semiconductor doped ups with half p-type and the other half n-type with a junction in between.
    2.  
       1.  
          • Bulbs B₁ and B₃
          • Diode D₃ and D₄ forward biased and D₂ and D₄ reverse biased
       2. Increase the kinetic energy of the electrons which make more of them gaining enough energy to jump ,from valency bond to conduction bond.
18.  
    1. Total resistance = (20×20) + 10Ω = 20Ω
                                    (20+20)
       I =  V  = 2.0V = 0.1A
            RT     20Ω
    2. V = IR
          = 0.1A × 10
          = 1.0V
    3. I = ^V/_R = 1.0V  = 0.05A
                       20Ω