Physics Paper 3 Questions and Answers - Momaliche Joint Pre Mock Exams 2022

• Answer all the questions in the spaces provided in this question paper.
• You are supposed to spend the first 15 minutes of the 2 ½ hrs allowed for this paper reading the whole paper carefully before commencing your work.
• Marks will be given for clear record of the observations actually 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 tables may be used.

Question 1 (20 marks)

You are provided with the following

• Two dry cell
• One bulb
• Voltmeter (0 – 3V)
• Ammeter (0 – 1A)
• Amounted nicrome wire mounted on a millimeter scale
• Switch
• Seven connecting wire at least two with crocodile clips
• Micrometer screw gauge

Proceed as follows:

1.  
   1. Set up the circuit as shown in the figure 1 below.
      
   2. With the crocodile clip at p, take the voltmeter reading and ammeter reading. Record v and 1 repeat the readings for L=80, 60, 40, 20 and 0cm respectively and complete the table below.                    (5mks)
      

      Length, L(cm)	100	80	60	40	20	0
      Voltage, V(V)
      Current, I (A)

   3. What changes do you observe on the bulb as L decreases from p? (1mrk)
   4. Plot a graph of ammeter reading (y=axis) against voltmeter readings. (5mrks)
   5. Determine the slope of the graph at V=1 volt. (2mrks)
   6. What physical quantity is represented by the slope of the graph at any given point?           (1mrk)
2.  
   1. Given the apparatus in a (i) above, draw a diagram of the circuit you would use to determine the current through the resistant wire and the potential difference across.     (1mrk)
   2. Set up the circuit you have drawn. Record the ammeter reading I and the wire reading V when       L=100cm       (2mks)
      V=…………………… I=………………………………………..
   3. Using a micrometer screw gauge, measure the diameter of the wire.          (1mrk)
      d=……………………………………………m
   4. Calculate the quantity:
      p= 0.785 (V) d² and give its units, where L is one meter.          (2mrks)
                        I   L

Question 2

• Vernier callipers
• Micrometer screw gauge
• Masses; 10g, 20g, 50g and 100g
• A helical spring
• Metre rule or half metre rule

Proceed as follows

1. Determine the number of complete turns of the helical spring.
   N = _______________________ (1 Mark)
2. Measure the external diameter of the spring using the vernier callipers
   D = _______________________ m (1 Mark)
3. Use the micrometer screw gauge to determine the diameter of the wire of the spring.
   d = ______________________ m (1 Mark)
4. Determine the value of m (2 Marks)
   N = 0.4D
           dm
5. Suspend the helical spring vertically alongside the clamped half metre rule as shown in figure 1 below. Determine the length L₀, of the spring before loading it.
   
6. Load the spring with a mass of 20g and determine the new reading on the metre rule. (L) Record this in the table below.
7. Calculate the extension e = L – L₀ due to the mass of 20g and record the value in the table given below. Repeat step f for other masses and complete the table.
   

   Mass (g)	0	10	20	30	40	50	60	70	80	90	100
   Weight (N)
   Reading (L) (cm)
   Extension e (cm)
   1/e (cm-1)

   (6 Marks)
8. Plot a graph of weight (N) against ¹/_e (cm^-1) (4 Marks)
9. Determine the slope (s) of the graph at a mass of 45g (2 Marks)
10. Given that m = −255T  
                             (S+60)² 
    Determine the value of T where (S) is the slope at 45g (3 Marks)

CONFIDENTIAL

QUESTION 1

Each candidate will require the following.

• A milliammeter.
• A voltmeter (0 – 3V) or (0 – 5V).
• A wire mounted on a mm scale (Nichrome wire SWG 32)
• A switch.
• A long wire with a crocodile clip at one end (crocodile clip to be used as a slider or jockey).
• A micrometer screw gauge (may be shared).
• 5 connecting wires, two with crocodile clips at the end.
• One new dry cell size D.
• Cell holder.

QUESTION 2
EACH STUDENT REQUIRES

• Micrometer screw gauge (shared between 4 students)
• Vernier callipers
• Masses
  
  • 10g
  • 2 – 20g
  • 50g
  • 100g
• Helical spring (K = 0.08N/cm)
• Metre rule or half metre rule
• Complete retort stand

MARKING SCHEME

Question 1 –(20 marks)

(a)

(ii)

Length, L(cm)	100	80	60	40	20	0
Voltage, V(V)	0.25	0.45	0.55	0.75	1.15	1.60
Current, I (A)	0.12	0.14	0.15	0.16	0.18	0.21

( ½ mk each –max5)

iii) Brightness increase.      1

 

iv) Axes -1

     Scale – 1

      Plotting – 2 at least four each ½ mark.

       Curve – 1

v) Tangent at the point

     Slope = 0.16 − 0.14       1 correct intervals
                    1.4 − 0.3

               = 0.02

                   1.1
              = 0.018Ω⁻¹

       1 correct evaluation.

vi)  Reciprocal of resistance 1

(b)
(i)

NB – ammeter in cell switch in series voltmeter parallel to wire.

ii) V=1.8V       1

    I=  0.14A     1

iii) d = 3.6x10^-4m   1

NB: Every teacher is expected to perform the experiment and adjust values given as appropriate.

 

Question 2.

a)N = 83✓

b)D = 0.0116M(4d.p) ± 0.0002✓1

c)d = 6.3 x 10^-4 m ✓1

d)N = 0.4D  ✓½

           dm

M = 0.4D =  0.4 x 0.0116    ✓1=0.0887  ✓½ (4d.p)
        dN      6.3×10−4×83

e)L_o = 50.0

f) Reading (L)
g)

 

Mass (g)	0	10	20	30	40	50	60	70	80	90	100
Weight (N)	0	0.01	0.02	0.03	0.04	0.05	0.6	0.7	0.8	0.9	1N
Reading (L) (cm)	50	51.2	52.4	53.6	54.8	56.0	57.2	58.4	59.6	60.8	62.0
Extension e (cm)	0	1.2	2.4	3.6	4.8	6.0	7.2	8.4	9.6	10.8	12.0
1/e (cm-1)	0	0.8333	0.4166	0.2777	0.2083	0.1666	0.1389	0.1190	0.1042	0.0926	0.0833

 h)

 Axes = ½mk well labelled unit a must.

    Scale = ½mk appropriate scale

     Plots = 2mks 8-11 plots correctly plotted

    4-7 correctly plotted 1mk

     Less than 4 - 0mks

    Smooth curve -1mk

i)Slope = 5.5 −  3.5 = 2.0 = 2.5NCM
               2.2     1.4    0.8

j)T = mx(5+60)²  ✓
           −255

      =  0.0887 x (2.5+60)²  ✓
                     −255

T=1.3588N²CM²  ✓