Physics Paper 3 Questions and Answers with Confidential - Sunrise Pre Mock Exams 2023

INSTRUCTIONS TO CANDIDATES

•  Answer ALL the questions in the spaces provided in the question paper.
• You are supposed to spend the first 15 minutes of the 2½ hours allowed for this paper reading the whole paper carefully before commencing your work.
• Marks are given for clear record of observations made, their suitability, accuracy and the use made of them.
• Candidates are advised to record their observations as soon as they are made.
• Non-programmable silent electronic calculators and KNEC mathematical table may be used.

QUESTION 1 (PART A)

You are provided with the following apparatus:

• A rectangular glass block.
• Four optical pins.
• A soft board.
• A protractor.
• 30cm ruler.
• 2 white plain papers.
• A plane mirror.
• A vernier calipers (to be shared)

PROCEDURE

1. Trace the outline of the glass block on the white paper.
2. Draw a normal ON, 2cm from point X on side XY.
3. Measure an angle (i) 10º from the normal.
4. Place back the glass block on the outline and fix a plane mirror vertically along the length of the glass block on the opposite side of XY using a cello tape as shown in the figure below.
   
5. Fix two pins P₁ and P₂ as shown in the figure.
6. By observing image of P₁ and P₂ , locate two pins P₃ and P₄ such that they appear to be in line with images of P₁ and P₂ .
7. Remove the pins and the block. Join P₃P₄ and produce the line to meet line P₁P₂ produced
8. Measure the perpendicular distance y.
9. Repeat the same for angles of 15º, 20º, 25º, 30º, 35º and 40º and record the results in table 2 below.
   (NB: The paper work must be submitted together with the question paper).
   Table 2
   

   Angle i	10°	50°	20°	25°	30°	35°	40°
   y(cm)

   (6marks)
10. Plot a graph of y(cm) against angle i. (5marks)
    1. Use the graph to determine y o the value of y when i = 0º
       y_o = ……………… cm (1mark)
    2. Measure and record the breadth (b) of the glass block
       b = ……………. Cm (1mark)
    3. Determine the value of η given that.        (1marks)
       η =  b 
              y_o

PART B

You are provided with the following:-

• A boiling tube.
• Some dry sand.
• A liquid in a measuring cylinder labelled L.
• Half metre rule.
• A vernier calipers (to be shared).
• A weighing machine (to be shared).
• Tissue paper.
• A measuring cylinder.

Proceed as follows:

1. Measure the length of the boiling tube.
   h = ……………………. cm (1mark)
2. Put a little amount of sand in the boiling tube and place it in the measuring cylinder which is almost filled with liquid L. Add sand, little by little until the tube floats upright as shown in figure below.
   
   Measure the length, d, of the boiling tube which is above the liquid using half metre rule
   d = …………… cm (1mark)
3. Determine the length, t, of the boiling tube which is immersed in the liquid using half metre rule
   t = ………….. cm (1mark)
4. Remove the boiling tube from the measuring cylinder, wipe it dry (on the outside) and measure its mass, m, including the sand inside.
   m = ………….. g (1mark)
5. Measure the external diameter, D, of the boiling tube.
   D = ………….. cm (1mark)
6. Determine the external radius, R.
   R = …………… cm (1mark)
7. Using the formula m = 12ρπR², determine ρ for the liquid.         (1marks)

QUESTION 2

You are provided with the following:

• An ammeter (0 – 1 A)
• A voltmeter (0 – 3 V or 0 – 5 V)
• A variable resistor
• A 10Ω carbon resistor
• A piece of resistance wire
• Two new dry cells
• A cell holder
• A switch
• Seven connecting wires

Proceed as follows:

1. Take the resistant wire and coil it around the biro pen to make a coil.
2. Set up the apparatus as shown Figure 5 below such that the 10Ω carbon resistor and the coil are in parallel connection.
   
3. Close the switch and the adjust the variable resistor such that the ammeter read a current of
   I₁ = 0.08A and record the corresponding voltmeter reading V₁
   1. V₁ =………………… (1mark)
   2. Calculate resistance R₁ = V₁  (1mark)
                                                 I₁
4. Repeat (c) above for current of I₂ = 0.16A and record the corresponding voltmeter reading V₂
   1. V₂ =………………… (1mark)
   2. Calculate resistance R₂ = V₂  (1mark)
                                                 I₂
5. Find the average value of resistance R (1mark)
6. Determine the resistance, C of the coil (2marks)
7. Now set up the apparatus as shown in Figure 6 below such that the voltmeter is connected across the cells, 10Ω carbon resistor and the coil are in parallel connection.
   
8. Close the switch and the adjust the variable resistor such that the ammeter reads a current of 0.04A and note the corresponding voltmeter reading. Record the value in the Table 4 below.
9. Repeat (h) above for other values of current and voltage and complete the Table 4 below
   Table 4
   

   Current, I (A)	0.04	0.08	0.12	0.16	0.20	;0.24
   Voltage, V(V)

   (4marks)
10. On the grid provided plot a graph of Voltage, V (V) against Current, I (A).   (5marks)
11. Determine the slope of the of the graph (2marks)
12. Given that graph is related to equation E=V+Ir where E and r are the emf and internal resistance of the cells respectively, use your graph to determine the value of:
    1. E =…………………… (1mark)
    2. r =……….…………. (1mark)

CONFIDENTIAL

Question 1

1. Rectangular glass block.
2. Optical pins.
3. Soft board.
4. Protractor
5. 30cm ruler.
6. Plain paper
7. Plane mirror
8. Some dry sand.
9. Water in a measuring cylinder labelled L.
10. Vernier calipers. (To be shared).
11. Half metre rule.
12. Tissue paper.
13. Weighing machine (to be shared).
14. A boiling tube

Question 2

• A cell and cell holder
• Switch
• A resistance wire mounted on a millimeter scale( Gauge 28 or 32)
• Six connecting wires each with a crocodile clip on one end.
• An ammeter (0 − 1A)
• A voltmeter ( 0 − 2.5V or 5V)
• A micrometer screw gauge( May be shared)

MARKING SCHEME

QUESTION 1

 PART A

(i) Table 1

                        (Check trend)
 6 marks – max 6 correct.
1 mark – Each correct 

(J) Graph (5 marks)

1. y_o = 4.9cm ✓¹ (y – intercept of student)
2. b = 6.1cm ± 0.1 ✓¹
3. η = b  = 6.1
         y_o    4.9
      = 1.245 ✓¹

PART B

1. h = 15cm ± 1cm ✓1(must be to 1.d.p)
2. d = 2cm± 1cm  ✓ [Use students value] (must be to 1.d.p)
3. t = h – d
    = 15 – 2(must be to 1.d.p)
   = 13cm ✓ [Use students substitution of c and d]
4. M = 61.2 ± 10g✓ [Use students value]
5. D = 2.53cm ± 0.1cm  ✓(must be to 2.d.p)
6. R = 2.53 = 1.265cm ✓
            2
7. M = 12ρπR²
   ρ =    M     
         12πR^2.   ✓Correct substitution
   = 1.014gcmˉ³ ✓

QUESTION 2

(C)
i) V₁ =    0.35 V +  0.10V      at least 1d.p                                                     (1mark)
ii)                                            (1mark)
Correct substitution                                                            ½ mk
Correct evaluation to 4 s.f or exact                                  ½ mk
If missing unit deny            ½mk
If wrong units Penalize      ½mk   

d) i) V₂ =     0.70 V+ 0.10V              at least 1d.p                                                     (1mark)

ii)       (1mark)
Correct substitution                                                            ½ mk
Correct evaluation to 4s.f or exact                                   ½ mk
If missing unit deny            ½mk
If wrong units Penalize      ½mk   

e)                                 (1mark)
Principle of averaging shown                                ½ mk
Correct evaluation to 4s.f or exact                                   ½ mk
If missing unit deny ½mk
If wrong units Penalize      ½mk

f)                         (2marks)
Application of the formula  ¹/_R = ¹/₁₀ + ¹/_C or R = 10C   1mk
                                                                                 10+C
Correct evaluation of C to 4s.f or exact                                       1mk
If missing unit deny                        1mk
If wrong units Penalize      1mk

h) 

(4marks)

j)                                                                                                                                  (5marks)

k)                                                                                                                                (2marks)
Change in y                                                    ½mk
Change in x                                                   ½mk
Correct evaluation to 4s.f or exact                       1mk
If missing unit deny            ½mk
If wrong units Penalize      ½mk

l) E =   y – intercept.                                                                         (1mark)
To be read from the graph, so graph should be extrapolated. 
If missing unit deny ½ mk
fully if graph not extrapolated
r =       Slope                                                                                     (1mark)
Ignore sign
If missing unit deny ½mk