# 2019 KCSE Physics paper 3 Past Paper-Free KCSE Past Papers with Answers.

## Practical

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 X

Proceed 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.

(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.

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