KCSE Past Papers 2019 Physics Paper 3 (232/3)

2019 Physics paper 3

Question 1

You are provided with the following:

• A stirrer
• A stond, a boss rind a clump
• A themionieter
• An aninieter
• A voltmeter
• A beaker
• A source of boiling water
• Two dry cells in a cell holder
• A switch
• Seven connecting wires
• A component labelled XProceed as follows:

  (a) Set up the circuit as shown in figure 1.

  

  Close the switch, read and record the current I through component X and the potential difference V across it. (l mark)I =……………………..

  V =……………………….

  Open the switch.

  Determine the resistance R of component X given that: R = V/I

  (b) Pour hot water into the beaker and set up the apparatus as in figure 2, so that component X afid the llieriiioirieter bulb are fully immersed.

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• (c) Stir the water from time to time, when the temperature falls to 80°, switch on the circuit, read and record the current I and the potential difference V in table 1. Then open the switch.(d) Repeat (c) as the temperature falls to the oÎher values shown in table 1. Complete the table. Table 1 (8 marks)
• 
• (e) ( i) On the axis provided, plot a graph of Log R against log T. (4 marks)
• (ii) Determine the slope S of the graph. (3 marks)(ii) Given that R and T are related by the equation Log R = Log K + n Log T (4 marks)

  (i) n…………………………..(1 marks)

  (ii) k…………………………..(2 marks)

  Question 2

  You are provided with the following:

   

• A metre rule
• A stand, boss and clamp A piece of string
• A 20 g mass
• A 50 g mass
• A measuring cylinder containing water
• A concave mirror
• A screen
• A candle
• Pieces of sewing threads
• A mirror holder (Lens holder)Proceed as follows:

  PART A

  (a) Using a string, suspend the metre rule on the stand so that it balances horizontally at its center of gravity.

  Record the centimetre mark at which the metre rule balances.

  Centimetre mark =………………….cm (1 mark)

  (b) With the metre rule balanced at its centre of gravity, suspend a 20 g mass at a distance of 30 cm from the centre of gravity.

  Suspend the 50 g mass on the other side of the centre of gravity and adjust its position until the rule is balanced. See figure 3.

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• Record the distance d of the 50 g ninss from the centre of gravity.d = ……………………….

  d = ……………………… (1 mark)

  Record the volume of the water in the measuring cylinder provided.

  V=……………………………….(1 mark)

  (ii) Immerse the 20 g mass fully into the water and adjust the position of the 50 g mass so that the rule balances horizontally.

  Record the volume V₁ of the water plus 20 g mass and the distance d₁ of the 50 g mass from the centre of gravity.

  (iii) (I) Determine the volume of the water displaced (1 mark)

  (II) Determine the weight of the water displaced. (density of water — I gcm(^-3) (3 marks)

  (d) (i) Use the principle of moments to determine the apparent weight of the 20 g mass when fully immersed in water. g — 10 Nkg^-1 (2 marks)

  (ii) Calculate the weight of the 20 g mass in air (g = 10 Nkg^-1)

  (iii) Determine the apparent loss in weight of the 20 g mass. (l mark)

  PART B

  (e) Light the candle and place it at distance u = 20 cm in front of the concave mirror. Adjust the position of the screen until a sharp image of the candle flame is obtained. See figure 4.

  

• (i) Read and record the distance v between the screen and the mirror.v=………………………………(1 mark)

  (ii) Determine:

  I. The magnification m of the mirror given that: m = v/u (1 mark)

  II. the value f₁ given that: f₁ = mu/m+1

  (f) Repeat part (e) for distance u₁ = 18 cm.

  (i) Read and record the distance v₁ between the screen and the mirror. (ii) Determine the magnification m₁ of the mirror. (1 mark )

  (iii) Hence determine f₂.

  (g) Determine the average value of f. ₁