Physics Paper 3 Questions And Answers with Confidentials - Form 3 Term 2 Opener Exams 2021

PHYSICS
PAPER 3
TERM 2 OPENER EXAM

INSTRUCTIONS

• Answer all questions
• You are not allowed to start working with the apparatus for the first ¼ hours of the 2½ hours allowed for this paper. This time is to enable you read the question paper and make sure you have all the apparatus you may need.
• Marks are given for a clear record of the observations actually made, for their suitability and accuracy and the use made of them.
• KNEC Mathematical tables and silent electronic calculators may be used in calculations.

1. 1. PART A
      You are provided with the following:
      • A cotton thread (about 12m long)
      • A 200ml beaker
      • A thermometer
      • A complete retort stand
      • 100ml measuring cylinder
      • A calorimeter with a stirrer
      • Some water
      • A heat source
      • A 100g mass
      • A balance
        
        Proceed as follows:
        1. Fill the 200ml beaker to about half its volume with water. Clamp the thermometer and lower it into the water, ensuring that its bulb does not touch the base or sides of the beaker. Tie the 100g mass with the thread securely and gently lower it into the water as shown below;
           
        2. Weigh the mass of the empty calorimeter and record it.
           Mass (M_c)= _________________g (½ mark)
        3. Measure 90ml of water and gently transfer it into the calorimeter. Measure and record the temperature of the water in the calorimeter.
           θ₁ = ________________ºc (½ mark)
        4. Determine the mass of water in the calorimeter by weighing both the water and the calorimeter.
           M_w = ________________ g (1mark)
        5. When the water with the 100g mass has started to boiling note and record the temperature
           θ_s of the solid.
           θ_s = ________________ ºc (½ mark)
        6. Quickly transfer the hot solid into the water in the calorimeter and cover it. Ensure that the calorimeter is well lagged. Stir gently and note the final steady temperature of the mixture.
           θ₂ = ________________ºc (½ mark)
        7. Given that M_sC_s (θ_s−θ₂)=(M_cC_c+M_wC_w)(θ₂−θ₁)
           Where:
           M_s =Mass of the solid
           M_c =Mass of the calorimeter
           M_w =Mass of water in the calorimeter
           C_w =Specific heat capacity of water = 4200J/Kg/K
           C_c =Specific heat capacity of the calorimeter =400J/Kg.
           Find the value of Cs the specific heat capacity of the solid. (3marks)
   2. PART B
      You are provided with:
      • Two dry cells size D
      • One voltmeter
      • One ammeter
      • Six connecting wires with crocodile clips
      • A potentiometer
      • A switch
      • A cell holder to hold two cells
      • A bulb and bulb holder
        1. Set up the circuit as shown below:
           
        2. Close the switch S and adjust the potentiometer till the bulb lights brightest. Record the ammeter and voltmeter readings
           I = ______________________A (1 mark)
           V = ______________________V (1 mark)
        3. By adjusting the potentiometer, obtain the corresponding readings of current for the values of the voltmeter readings given in the table below.
           

           Voltmeter Reading V(V)	0.1	0.3	0.5	0.8	1.0	1.2	1.5	1.7
           Ammeter Reading I(A)

           (4marks)
        4.    
           1. Plot a graph of voltmeter reading (V) against ammeter reading (A) (5 marks)
           2. From your graph, determine the resistance of the bulb when the voltmeter reading is 0.5V. (3marks)
2. You are provided with the following;
   • An optical bench or metre rule
   • A convex lens and lens holder
   • A candle stick
   • Screen I with a hole and crosswires at its centre
   • Screen II
   • A wooden block
   • A vernier calipers (to be shared)
   • Weighing balance (to be shared)
     
     Proceed as follows:
     1. PART A
        1. By focussing on a distant object e.g a window, obtain an estimate for the focal length of the convex lens.
           Focal length = _____________________cm (1 mark)
        2. Place the screen I at the zero mark of the metre rule on the optical bench (It should remain at this point throughout the experiment). Then place screen II at the distance L = 45cm. Light the candle and stand it in position to light up the cross wires. Put the convex lens on the lens holder and adjust its position between the two screens such that you obtain a sharp magnified image of the cross wires on screen II. (See figure 1)
           Figure 1
           
        3. Read the mark for the position of the lens holder on the metre and hence record the distance in table 1.
        4. Repeat the procedure above for other values of L and complete table 1.
           Table1
           

           L (cm)	U (cm)	(L – U) (cm)	P=U(L – U) cm2
           45
           50
           60
           70
           90
           100

           (5 marks)
           
           
        5. On the grid provided, plot a graph of P (y-axis) against L (5 marks)
        6. Determine the slope of the graph. (3 marks)
           
           
     2. PART B
        1. Take the wooden block and using the vernier callipers provided measure and record the;
           Length = ___________________ cm = ________________m (1 mark)
           Width = ___________________ cm = ________________m (1 mark)
           Thickness = ___________________ cm = ________________ m (1 mark)
        2. Take the same wooden block in (g) above and using the weighing balance determine its mass
           Mass = ___________________g = ________________kg (1 mark)
        3. Using the values obtained in (g) and (h) above, determine the density of the wooden block giving the answer in SI units. (2 marks)

CONFIDENTIAL

QUESTION 1
Each candidate will require the following

• A retort stand, clamp and boss
• A spiral spring (k= 10 N /m)
• A stop watch
• Three 100g masses
• Three 50g masses
• 5 optical pins
• A rectangular glass block (100x 60x 18 mm)
• A white plain paper
• A soft board
• 4 thumb pins

QUESTION 2
Each candidate should be provided with

• two retort stands
• a metre rule
• some cotton thread (approximately 1.2m long)
• a ball of plasticine
• a stop watch
• a protractor
• half metre rule

MARKING SCHEME

1.    
   1. PART A
      2. Mc = 60g ✔½ (work with the students value)
      3. θ1=27 ± 1oC ✔½
      4. Mw = 90g ✔1
      5. s = 98oC or 100oC ✔½
      6. 2 = 34oC 1oC ✔½
      7. Cs = 0.06 ×400×7+(0.09 ×4200 ×7)
                         0.1 ×66✔1
         = 2.8146.6✔1
         = 426.36 J/kgk✔1
         
         
   2. PART B
      10. 
          

          Voltmeter Reading V(V)	0.1	0.3	0.5	0.8	1.0	1.2	1.5	1.7
          Ammeter Reading I(A)	0.08	0.14	0.16	0.18	0.19	0.2	0.23	0.25

          ½ mk each correct value. Maximum 4 marks
      11.    
          1. Graph
             
          2. Slope = ^1-0/_0.2-0.12 ✔1 (correct substitution)
             = 10.08
             = 12.5 Ω ✔1 (Correct evaluation with correct unit)
2.     
   1. PART A
      1. Focal length estimate = (9.5 – 10.5)cm ✔
      2.   
      3.      
      4.   
         

         L (cm)	U (cm)	(L – U) (cm)	P=U(L – U) cm2
         45	16.0	29.0	464.0
         50	14.3	35.7	510.5
         60	13.5	46.5	627.8
         70	12.4	57.6	714.2
         90	12.2	77.8	949.2
         100	12.0	88.0	1056.0
         	@½mk total 3mks	> 4 correct 1 mark	> 4 correct 1 mark

      5.      
         
      6. Taking points (40, 410) and (89, 940) ✔
         (Check indication on the graph)
         Slope = 940-41089-40 ✔
         = 108 cm
         (9.0 – 11.0)cm✔
         
         
   2. PART B
      1. Length = 5.14 cm ✔½ = 0.0514m ✔½
         Width = 3.42cm ✔½ = 0.0342 m✔½
         Thickness/ height = 1.04cm✔½ = 0.0104m ✔½
         Total 3 marks
         Values should be recorded to correct degree of accuracy
         
         
      2. Mass = 15.8g✔½ = 0.0158kg ✔½
         Total 1 mark
      3. Volume = 0.0514 x 0.0342 x 0.0104
         = 1.828 x 10-5 m3✔
         Density = ^mass/_volume
         = ^0.0158/_1.828 × 10^-5
         = 864.24 kg / m^-3
             Range ±10