PHYSICS PAPER 3 - KCSE 2019 MASENO MOCK EXAMINATION (WITH MARKING SCHEME)

1. PART A
   You are provided with the following:
   • a voltmeter (0 – 5V)
   • a carbon resistor labelled R
   • Two new size D dry cells
   • cells holder
   • a capacitor labelled C (2200µF)
   • a stopwatch
   • eight connecting wires at least four of which have crocodile clips
   • a switch
     Proceed as follows :
     1.  
        1. Draw a circuit diagramhaving a switch, voltmeter, two dry cells and connecting wires that can be used to determine the Emf of the cells provided. (1mk)
        2. Use the above circuit to determine the Emf of the cells
     2. Connect the circuit as shown in figure 1 below.
        
     3. Close the switch and note the maximum voltage attained on the voltmeter. Record it as V_max
     4. Open the switch and simultaneously start your stopwatch and note the time taken for the voltmeter reading to decrease from V _max to 0.2V. record this value in table 1 below. Short the terminals of the capacitor C to attain a reading of zero volts on the voltmeter.
     5. Repeat procedure iii and iv for the other values of the voltage indicated in table 1
        

        Voltage, V (volts)	0.2	0.5	0.8	1.0	1.5	1.8
        Time (t)(s) taken for voltage to decrease from V maxto V

        determine the resistance R of the resistor given that t =⁷⁰/₁₁ CR. Where t is the time at which V=0.5V and C is the capacitance of the capacitor. 3mks  
2. PART B
   You are provided with:
   • A complete stand
   • A stop watch
   • A light string
   • A pendulum bob or a 50g mass
   • A metre rule or a half metre rule
     Proceed as follows:
     1. Set up the apparatus as shown in the figure below
     2. Displace the bob slightly at a small angle from the vertical line and record the time taken 20 oscillations in the table below. Repeat the for two more trials
        

        Trials	Trial 1	Trial 2	Trial 3
        Time for 20 oscillations

        Find the average time for 20 oscillations    ( 1½ mks )  
     3. Calculate the average periodic time T_{av  (}2mks)
     4. Given that T_av=2π find the value of g     (3mks)
3. PART C
   You are provided with the following:-
   • A biconvex lens.
   • A lens holder.
   • A screen.
   • A meter rule.
   • A candle
   • A cross wire
     Proceed as follows:
     1. Set up the apparatus as shown in the figure below.
        
        NB: THE CROSS WIRE PROVIDED MUST BE PLACED JUST INFRONT OF THE CANDLE TO ACT AS THE OBJECT     
     2. Place a lit candle and a cross wire at a distance U = 20cm from the len
     3. Adjust the position of the screen until a sharp image of the cross wire is focused on the screen. Record d in the table 2.
     4. Repeat part (b) and (c) for other values shown in table 2 and complete the table. (8mks) 
        

        U(cm)	20	25	30	35	40	45
        D (cm)
        V=D-U(cm)
        1/m = u/v

        determine the slope S of the graph             (3mks)
        Plot a graph of ¹/_m against U. (5mks)
     5. given that ¹/_f=¹/_v +¹/_u,   use the graph to determine the focal length of the lens (4mks)

MARKING SCHEME

1. QUESTION ONE
   PART A 
   Emf…………3.0V ±0.1           correct to 1 dp
   V max........2.5 V±0.1         correct to 1 dp
   

   Voltage, V (volts)	0.2	0.5	0.8	1.0	1.5	1.8
   Time (t)(s) taken for voltage to decrease from V max to V	23.72	14.03	10.16	8.12	4.78	3.07

   
   Correct substitution        (1mk)
   Correct evaluation          (1mk)
   Correct answer within 1000±50Ω with correct units 4sf   (1mk)
   NB ½ MARK FOR NO UNITS, NO MARK FOR WRONG UNIT
   
   PART B
   

   Trials	Trial 1	Trial 2	Trial 3
   Time for 20 oscillations

   Answers within       29.94   ±3s
   ¹/₂ mk for the principle of averaging  
   1 mk for correct answer using the learners values
   
   NB; ½ MARK FOR NO UNITS, NO MARK FOR WRONG UNIT
   T_av=answer in vi above ÷20     
   1mk correct substation 
   1mk correct answer
   
   NB ½ MARK FOR NO UNITS, NO MARK FOR WRONG UNIT
   Correct substitution     1mk    
   Correct evaluation       1mk
   Correct answer             1mk 
           
2. QUESTION 2
   

   U(cm)	20	25	30	35	40	45
   D (cm)	75.0	62.0	60.0	62.0	64.0
   V=D-U(cm)
   1/m =u/v

   Axis       (1mk)   both well labeled with units
   Scale     (1mk)    simple and uniform
   Plotting (2mks)   each correctly plotted point within 1 small square
   ½ a mark a maximum of 4 pts
   Curve   ( 1mk)   a smooth curve through at least four correctly plotted pts
   Change in y      (1 mk)
   Change in x       (1 mk)
   Correct evaluation with correct units   (1mk)    
   NB: ½ MARK FOR NO UNITS, NO MARK FOR WRONG UNIT
   
   Rearranging ¹/_f =¹/_v+¹/_u to ^u/_v=^u/_f-1   (1mk)
   Identifying that slope =¹/_f           (1mk)
   Correct evaluation           (1mk)
   Answer with correct units      (1mk)   within   15±2 cm
   NB ½ MARK FOR NO UNITS, NO MARK FOR WRONG UNIT