## KCSE 2017 Physics Paper 3 with Marking Scheme

INSTRUCTIONS TO CANDIDATES

• Marks are 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 calculator may be used.
• Candidates should answer the questions in English
1. You are provided with the following:
• One dry cell in a cell holder
• One milliammeter
• A resistor labelled R1
• A chain of six resistors
• A switch
• Connecting wires

Proceed as follows:
1. Set up the circuit as shown in Figure 1 Switch on the circuit to obtain a positive deflection in the milliammeter. Record the reading I1 of the milliammeter.
I1 = ...................mA    (1 mark)
2. Remove the crocodile clips from the ends of the chain of resistors and connect them across two resistors in the resistance chain that add up to 3.0 kΩ. Record the reading of the milliammeter I2
I2 = ...................mA  (1 mark)
3. Repeat the procedure in (b) for other values of resistance R shown in Table 1 and complete Table 1.

(Hint: The values of R may be obtained by combining two or more resistors in the chain)

Table 1
(6 marks)

 R × 103 (Ω) 0.330 1.0 1.33 1.5 2.5 4.0 I(mA) I x 10−3 (A) 1/I (A−1)
4. Plot a graph of 1/I (y-axis) against R     (4 marks)
5.
1. Determine teh slope S of the graph. (3 marks)
2. Given the equation E = 1(R + R1) determine the values of:
1. E      (3 marks)
2. R1    (2 marks)
2. You are provided with the following:
• Triangular glass prism
• Four optical pins
• Some cellotape
• A soft board
• A plain sheet of paper ( provided by KNEC)
• A source of boiling water
• A 250ml beaker
• A thermometer
• A stopwatch

Proceed as follows:

PART A:
1. Fix the plain sheet of paper on the soft board using some cellotape. Place the triangular prism on the paper and trace its outline on the sheet of paper. Remove the prism and use a ruler to extend the three sides of the outline. See Figure 2. Measure angle A and the length l.
A = .......... (1 mark)
= .........cm 91 mark(
NB: The plain sheet of paper must be submitted together with the question paper.
2. At a point about a thirdway along one side of the outline from angle A, draw a normal.
(2 marks)
3. Draw a line at angle i = 40° to the normal. Stick two pins P1 and P2 vertically on this line. (see Figure 3). Place the prism accurately on the outline. By viewing through the opposite side, stick two other pins P3 and P4 vertically such that they are in line with the two images of pins P1 and P2
4. Remove the prism and the pins. Draw a line joining the marks made by P3 and P4 Extend lines P1 P2 and P3 P4 to intersect. Hence measure the angle of deviation D.
D = ............... (1 mark)
5. For two other values of angle i shown in Table 2 locate and measure the corresponding angles of deviation. Complete Table 2.

Table 2    (2 marks)

 i 40° 50° 60° D
6.
1. Determine the average value Dm of D.   (1 mark)
2. Determine the constant k using the equation;     (3 marks) PART B
(Read all the instructions before starting this part)
7. Using the thermometer measure and record the temperature of the room°
θ0 = ....................................... °c   (1 mark)
8. Using the 250 ml beaker, collect 200 ml of hot water from the boiling water source. Place the thermometer into the hot water and wait until the water cools to 80°C then start the stopwatch and record the time t, it takes the water to cool to 75°C.
t1 = .................... seconds   (1 mark)
9. Wait until the water cools to 70°C then start the stopwatch and record the time t2 it takes the water to cool to 65°C.
t2 = .................. seconds    (1 mark)
10. Determine the rate of temperature change X and Y in the two time intervals;
1. X = 77.5 − θ0      (2 marks)
t1
2. Y = 67.5 − θ0    (2 marks)
t2
11. State with a reason how the rate of change of temperature between 90°C to 85°C compares with X.     (2 marks)

## MARKING SCHEME

1.
1. I1 = 0.3mA  (1 mark)
2. I2 = 0.37mA  (1 mark)
3.
 R × 103 (Ω) 0.33 1 1.33 1.5 2.5 4 I(mA) 0.69 0.53 0.48 0.44 0.35 0.26 I x 10−3 (A) 0.69 0.53 0.48 0.44 0.35 0.26 1/I (A−1) 1.45 1.88 2.08 2.27 2.86 3.84
(6 marks)
4. attach graph of 1/I against R 5.
1. Slope = 2.5 − 1
2.5 − 0
=0.60   (3 marks)
2.
1. (I) 1/IR/ER1/E
1/I 1/E (R + R1)
∴ 1/E = Slope = 0.6
E = 1/0.6 = 1.67    (3 marks)
2. R1 =  R1 = y intercept
E     1.67     (2 marks)
2.
1. A = 60°    (1 mark)
l = 5.2cm    (1 mark)
2. Normal at 3rd way  1.5 from A  (2 marks)
(From the candidates outline)
3.
4.
5. D1 = 41°  (1 mark)
D2 = 39°   (1 mark)
D3 = 40°  (1 mark)
6.
1. Dm = 41° + 39° + 40° = 40° (1 mark)
3
2. = sin 50
sin 30
= 1.53   (3 marks)
7. θ0 = 24°C   (1 mark)
8. t1 = 1.59sec
9. t2 = 3.00sec
10.
1. X = 77.5 − 24  (2 marks)
1.59
= 33.65
2. Y = 67.5 − 24  (2 marks)
3.00
=14.5
11. It is greater than X because the cooling rate depends on the difference between the highest temperature and the room tempeature.   (2 marks)