Physics Paper 1 Questions and Answers - Form 4 End Term 1 Exams 2023

1. Attempt all the questions in the spaces provided
2. Take g= 10N/kg

1. A micrometer screw gauge has a zero error of −0.02mm. It is used to measure the diameter of a wire. If the actual diameter of the wire is 0.28mm. Draw the micrometer screw gauge showing the diameter of the wire.                                  (2 marks)
2. The following figure shows the path of a ray of light through a transparent material placed in air.
   
   Determine the refractive index of the transparent material              (2 marks)
3. A tube of radius 9 mm has a constriction of diameter 10mm. Water flows in the tube at 3ms^-1. Determine the velocity of water in the constriction.    (3 marks)
4. A faulty thermometer reads 2°C when dipped in ice at 0°C and 95°C when dipped in steam at 100°C. What would this thermometer read if placed in water at room temperature at 18°C?       (3 marks)
5. Using Kinetic theory of matter, explain why solids expand when heated                (2 marks)
6. The height of a mountain is 1360m. The barometer reading at the base of the mountain is 74cmHg. Given that the densities of mercury and air are 13,600Kgm^-3 and 1.25Kgm^-3 respectively, determine the barometer reading at the top of the mountain.               (3 marks)
7. The chart below shows part of the electromagnetic spectrum. 
   

   A

   B

   Visible light

   UV light

   C

   1. Identify the radiation marked A and C. (1mark)
   2. Give one application of the radiation marked B. (1mark)
8. An electric kettle is rated at 1.8 kW, 240 V. Explain the choice of the safest fuse for the kettle. (the available fuses are 5 A, 10 A, and 20 A)          (2marks)
9.  
   1. A bar magnet is pushed into a coil as shown in Figure 5 below.
      
      Explain what happens to the pointer of the galvanometer when the magnet is:
      1. Moved into the coil rapidly?                    (1mark)
      2. Remains stationary inside the coil?        (1mark)
   2. State one way of increasing the magnitude of induced current in a generator.        (1mark)
   3. A transformer has 200 turns in the primary coil and 1000 turns in the secondary coil. The primary coil is connected to an a.c source producing 100 V and rated 500 W. The current delivered by the secondary circuit was found to be 0.95 A.
      1. Determine the efficiency of this transformer.        (3marks)
      2. Explain why the efficiency is less than 100%.         (2marks)
      3. State Lenz’s law of electromagnetic induction.          (1mk)
10. The figure below show three wooden blocks resting on a flat surface.  (They are of the same material).
               
    1. Arrange them starting from the least stable.         (1mark)
    2. State the factor that you have considered in 2(i) above.         (1mark)
    3. State Faraday’s law of electromagnetic induction.         (1 mark)
11. Figure below shows a cathode ray tube (C.R.O).
             
    1. Name the parts labelled A and B. (2mks)
    2. What are the functions A and C?           (2mks)
    3. Explain how electrons are produced.           (1mk)
    4. Give a reason why the tube is evacuated.           (1mk)
12.  
    1. What is the purpose of a fuse?                                (1 mark)
    2. The diagram in figure below shows a ring – main circuit used by an electrician in a certain house.
       
       1. Identify two faults in the installation.                                             (2 marks)
       2. Explain why the 3 – pin plug fuse has a longer earth pin than the live and neutral pins.   (1 mark)
       3. Identify the type of transformer T used in the diagram in Figure                                     (1 mark)
    3. A cooker rated 2.0kW was operated for 40minutes each for 30days. If the cost of each   kilo – watt – hour unit is Shs. 15.50, calculate the cost of electricity used.             (3 marks)
13. State two properties of cathode rays.                                                                                     (2mks)
14.  
    1. A power station has input of 50kw at p.d. of 10 Kv. A transformer with secondary coils of 1000 turns is used to step down the voltage to 1000v for transmission along grid. Assuming there is no power loss, calculate:
       1. Current in primary coil.                                                                                               (2mks)
       2. Number of turns in primary coil.                                                                               (1mks)
    2. State which of coils in thicker and why.                                                                 (1mk)

MARKING SCHEME

1.  
   
      0.28+0.02
   = 0.30mm
2. _an_g =  Sin 90°
              Sin 42° 
   _an_g =     1      = 1.494
              0.669
3. Rate of flow; a₁  v₁ =  a₂  v₂
   π × 0.009² × 3 = v2 × π × 0.005²
   v₂ = 9.72 ms^-1
4. 0------ 100   →           100 units         Reading  =  2  +  16.74
   2 ------ 95   →             93 units                          = 18.74°C
   1 unit        =     ⁹³/₁₀₀ = 0.93 units
   18 units    =   18 X 0.93
                   = 16.74
5. Heat increases the kinetic energy of molecules. This leads to increase in the distance covered by moving molecules, hence its length increases
6.       h₁ρ₁g   =  h₂ρ₂ g
   1360 x 1.25 = (74 – x)/100X 13600
       x = 61.5cm
7.  
   1. A-microwaves C- X-rays
   2. Heating e.g cooking, drying
8. I =   ¹⁸⁰⁰/₂₄₀ = 7.5 A               safest fuse = 10 A which is slightly above the operating current.
9.   
   1. 
      
      1. The pointer deflects to the left and then goes back to rest position (zero). Changing magnetic flux links the coil inducing an e.m.f which causes current to flow making the pointer to deflect.
      2. No deflection. There is no change in magnetic flux, no induced e.m.f and hence no current.
   2.  
      • Using a stronger magnet
      • Increasing the number of turns of the coil
      • Winding the coil on a soft iron core
      • Increasing the speed of rotation of the coil;;
   3.  
      1. Determine the efficiency of this transformer. (3marks)
         N_s  =  V_s
         N_p      V_p 
         V_s = 1000  x  100 = 500 V;
                  200
         Power output = 500 x 0.95 = 475 W;
         Efficiency = 475   x 100 = 95%;
                             500
      2. Explain why the efficiency is less than 100%.             (2marks)
         • Flux leakage
         • Hysteresis loss
         • Heating due to eddy current
         • Copper losses
           Nb: one well explained loss award 2mks
      3. Lenz law states that the induced current flows in such a direction that produces magnetic effect that oppose the charge producing it
10.  
    1. I, III, II ✓✓
    2. Position of centre of gravity. ✓✓
    3. The magnitude of induced e.m.f is directly proportional to the rate of change of magnetic flux. ✓1 mk
11.   
    1. 1. A – Control grid.
          B – Anodes. (2mks)
       2. A – Control the brightness/No. of electron to screen.
          C – Deflect the beam of electrons vertically. (2mks)
       3. Thermionic emission by heating the cathode directly or indirectly. (2mks)
       4. To reduce ionisation. (1mk)
12.  
    1. Protective device in mains electricity that melts when current exceeds the rating;
    2.  
       1. Switch should be on live wire and not neutral;
          Fuse should be on the live wire  ;
       2. To open the live and neutral earlier;
          Make contact earlier than live;
       3. Step down transformer
    3. 2 Kw X 40/60 X 30 =   40Kw-Hr
       40 X 15.50
       Sh 620
13.  
    • Travel in straight line
    • Charged     
    • Deflected by magnetic & electric fields any 
14.  
    1.  
       1. P =VI
          I =  50 000   = 5A
                10 000
       2. Ns  = Vs      Np = 1000 x 10 000  = 10 000 turns
          Np     Vp                      1000
    2. Primary coil to minimize resistance