Physics Paper 3 Kenya High Post Mock Exams 2020 with Confidentials - Questions and Answers

INSTRUCTIONS

• Answer all the questions in this paper
• You are supposed to spend the first 15 minutes of the 2 1/4hours allowed for this paper reading the whole paper carefully before starting your work.
• Marks are given for clear record of the observations made, their suitability and accuracy and the use made of them.
• Candidates are advised to record observations as soon as they are made
• Mathematical table and electronic calculators may be used.

Question 1

You are provided with the following apparatus

• Two dry cells
• A cell holder
• A bulb
• A voltameter
• An ammeter
• A switch
• Amounted resistance wire labelled AB

1. Set up the apparatus as shown in the circuit below.
   
2. With the crocodile clip at A (ie L = 100cm) take the voltameter reading (V) and the ammeter reading (I). Record V and I in the table below.
   

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

   (7 marks)
3. Repeat the procedure in (b) above for the lengths shown and complete the table above.
4. State the changes you observe on the bulb as L decrease from A. (2 marks)
5. Plot a graph of voltage against length (cm) (5 marks)\
6. What physical quantity does the slope of the graph represent at any given point. (2 marks)
7. From your graph determine the value of voltage at length L = 70cm. (2 marks)
8. Use your graph to describe how the physical quantity in (e) above is affected as the current increases. Explain why. (2 marks)

Question 2

You are provided with the following apparatus

• A complete stand
• Copper wire (wire length about 30cm)
• A stop watch
• A protractor
• A meter rule
• Corked optical pin

Procedure

1. Measure the length L of the copper wire.
   L = .................................................. m (1 mark)
2. Bend the wire to form an angle O of 60°, suspend it from the corked optical pin as shown in the diagram below.
   
3. Give it a small displacement so that it oscillates about a point on the pin. Measure the time, t(s) for 10 oscillations of the wire.
   t = ................................................. (s) (1 mark)
4. Repeat the procedure (b) above for the values of O = 70°, 80°, 90°, 100°, 110°.
5. Record and complete the results in the table below.
   

   θ (°)	60	70	80	90	100	110
   Cos ½θ
   Time for 10 oscillations, t (s)
   Periodic time T (s)
   T 2 (s2)
   1/T2 (s-2)

   (7 marks)
6. On the grid provided, plot a graph of  ¹/_T² (s^-2) against Cos ½θ. (5 marks)
7. Determine the slope. (3 marks)
8. Given that the graph is related by the equation ¹/_T² = 8π²LCos ½θ, determine the value of constant g.
                                                                                     g                                        (3 marks) 

CONFIDENTIAL

Question 1
Each candidate should have the following.

• Two dry cells (1.5v) D - size
• Cell holder(s) to enable parallel connection
• A bulb (1.5v)
• A voltameter
• An ammeter
• A switch
• Mounted resistance wire labelled AB
  (The wire is SWG 32 mounted on a metre rule on a mm sale.)

Question 2

• Complete stand
• Copper wire (length of about 30cm)
• A stop watch
• A protractor
• A meter rule
• Corked optical pin

MARKING SCHEME

1.  
   1.  
   2. 
      

      Length l(cm)	100	80	60	40	20	0
      Voltage (V)	0.10	0.15	0.20	0.2	0.45	1.00
      Current I (A)	0.04	0.05	0.07	0.09	0.12	0.16

   4. The bulb lights more brightly. (2 marks)
   5. Graph should be a smooth curve with positive slope
      A - 1mk
      S - 1mk
      P - 2 mks
      C - 1 mk
      Total (5 mks)
   6. The resistance of the bulb. (2 marks)
   7. Voltage at length L = 70cm
      Candidate value from the his/her graph.
      showing how to get it ....(1 mark) 0.75 ±.1
      Writing the value ...............1 mark
   8. as the current increases, the resistance also increases hence the bulb glows more brightly
2. 1. L = 0.3m (1 mark)
   3. t = 5.82s ( 1 mark)
   5. 
      

      θ (°)	60	70	80	90	100	110
      Cos ½θ	5.82	6.42	6.96	7.54	8.28	10.59
      Time for 10 oscillations, t (s)	0.582	0.642	0.696	0.754	0.828	1.059
      Periodic time T (s)	0.3387	0.4122	0.4844	0.5685	0.6856	1.1215
      T 2 (s2)	2.9525	2.4260	2.0644	0.5685	1.4586	0.8917
      1/T2 (s-2)	0.8660	0.8192	0.7660	0.7071	0.6428	0.5736

   6. graph is a straight line graph with a positive gradient (slope)
      A............. 1mk
      S ..............1mk
      P.............. 2 mks
      L.............. 1 mk
      5 mk