Physics Trial Exams Paper 3 Questions - Alliance Boys High School Mock December 2020

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Instructions to candidates

  1. Write your Name and Index number in the spaces provided above.
  2. Sign and write the date of examination in the spaces provided above. 
  3. Attempt all the question in the spaces provided.
  4. KNEC Mathematical tables and silent electronic calculators may be used.
  5. All working must be clearly shown where necessary.
  6. This paper consists of 10 printed pages, check to ascertain that all pages are printed.
  7. The answers should be in English.
  8. Assume:
    • Density of water to be / gcm-3
    • Specific heat capacity of water to be 4.2J/g/°C
    • Gravitational field strength to be 10Nkg-1


Question  Maximum Score  Candidate's Score 
 1  20  
 2  20  
 TOTAL  40  

You are provided with the following apparatus

  • A 20g mass, 50g mass and 100g mass 
  • A half metre rule
  • Vernier calipers (can be shared)
  • Micrometer screw gauge (can be shared)
  • A stop watch
  • A helical spring 
  • A retort stand, boss and clamp

Proceed as follows:

  1. Count and record the number of complete turns, N of the helical spring
    1. Number of complete turns, N=........................(1/2 mark)
      Using a Vernier calipers measure and record the internal diameter, d, and external diameter, d, of the helical spring
    2. Internal diameter, d1 (1/2 mark)
    3. External diameter, d2 (1/2 mark)
      Using the micrometer screw gauge measure and record the diameter, dy of the wire coiled to make the helical spring
    4. Diameter of wire, (1/2 mark)
      Using a half metre rule measure and record the length of the helical spring, h1), between the ends of the turns that make the helical spring. See Figure1a
    5. Length of helical spring, h1..................... cm (1/2 mark)
    6. Determine the number of turns per unit length of the helical spring (1/2 mark)
  2. Hang a mass of 150g on the spring. Measure and record in Table 1 the length h2, between the end turns of the coil. See Figure Ib. Hence determine the extension e (m) produced by the mass.
    figure 1 kjasuhd
  3. Displace the mass by a small vertical distance and release so that the spring makes vertical oscillations. Measure and record in Table 1 the time for 10 oscillations. Hence determine periodic time, T.
  4. Repeat the procedure in (b) and (c) above for 120g and 170g masses. Complete Table 1 (5 marks)
    Table 1
    Mass, m (kg)  0.120  0.150  0.170 
    Length of spring, h2 (cm)      
    Extension, e (m)      
    Time, t for 10 oscillations (s)      
    Period, T=t/10 (s)      
    α= mg/e      
    ? = 4π2m/T2      
  5. Compare the average values of α and ? (1 mark)

You are provided with the following:

  • A 400ml glass beaker
  • A thermometer
  • A stop watch
  • A tripod stand and a measuring cylinder 100ml
  • A wire gauze
  • A source of heat

Proceed as follows:
Set up the apparatus as shown in Figure 2
figure 2 kagusd
Using a measuring cylinder, measure 100 cm3 of water and pour it into the beaker.

  1. Measure and record initial temperature of the water, To
    To.................... (1/2 mark)
  2. Heat the water until boiling point, measure and record the boiling point temperature, Tb.
    Tb=........................ (1/2 mark)
  3. Calculate the average quantity of heat acquired by the water in raising temperature of water to boiling point (1/2 mark)
    Switch off the gas tap and place a thermometer into the beaker and start the stop watch when the temperature of water is 75 'C. Measure and record in Table 2, the temperature, T C of the water every two minutes.
    Table 2 (4 marks)
    Time (t) (minutes)  10  12 
    Temperature (T) °C            
    Excess temperature, (T-T0°C            
    Log (T-T0)            


  4. Complete Table 2

  5. Plot a graph of Log Excess temperature against Time (4 marks)

  6. From the graph determine:
    (i) the initial Excess temperature, K (1/2 mark)
    (ii)the temperature of the surrounding TR using the expression K= 75 - TR (1/2 mark)
    (iii)the average rate of loss of heat energy during the 12 minutes (1/2 mark)

You are provided with the following apparatus with an aim of using them to determine the focal length of a concave mirror.

  • A concave mirror
  • One stand, one boss and one clamp
  • An optical pin stuck on a stopper 
  • A mirror holder
  • A screen
  • A metre rule


  1. Sketch a ray diagram for principle you will use to determine the focal length of a concave mirror. (1 mark)
  2. Describe the procedure in your set up for measuring the focal length (1 mark)
  3. Assemble the above apparatus accordingly measure and record the focal length of the concave mirror (1 mark)

You are provided with the following apparatus

  • A voltmeter range (0-5V)
  • An ammeter( 0-14) 
  • 2 dry cells 
  • Cell holder 
  • Seven pieces of connecting wires
    A carbon resistor, Labelled, R 
  • Potentiometer
  • A Centre zero milliammeter (Galvanometer) 
  • A capacitor labelled C
  • 2 plug keys


  1. Sketch a diagram for an open circuit for a set up to use to measure electromotive force, E of a battery comprising two cells connected in series
    (1 mark)
  2. Set up the circuit, measure and record the electromotive force, E of the battery .......... (1 mark)
    Assemble appropriate apparatus in a closed circuit to investigate internal resistance of the battery. Measure several terminal potentials and their corresponding currents through the battery. Record your readings in Table 3.
    Table 3
    Voltmeter reading, V (V)      
    Ammeter reading, I(A)      
    (E - V) II      
  3. Complete Table 3 (41/2 marks)
  4. Use the results in Table 3 to determine the average internal resistance of the battery (1 mark)
    Record the capacitance. C of the capacitor in scientific notation
  5. Capacitance, C = ................(1 mark)
    Set up the circuit in Figure 3.
    last hjvad
    1. Close key S, while S, is open and describe the behavior of the pointer of the Milliameter (Galvanometer) (1 mark)
    2. State the inference for the observation in f{i}
    3. Open S, then close key S2 and describe the behavior of the pointer of the Galvanometer .....................(1 mark)
    4. State the inference for the observation in f(iii) (1 mark)
  7. Repeat to close key S1 until the pointer stops moving, then open key S2. Record the maximum current, Io = ............mA (1 mark)
  8. Close key S1 until the pointer stops moving, then open key S2 measure and record in Table 4 the time for the current to change from I0 to 0.8I0.
  9. Repeat this procedure in (h) for current to change to 0.5I0, and 0.4I(11/2)
    Table 4 
    Current (mA)  0.8I0  0.5I0  0.4I0 
    Time (s)      
  10. Use the measurements in Table 4 to determine the average half-life, t for the discharge of the capacitor (1 mark)
  11. Use the equation t=0.693 RC to evaluate the resistance R in the circuit. (11/2mark)
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