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PHYSICS
PAPER 3
MARCH, 2015
TIME: 2 ½ HOURS.
CHEPALUNGU SUB- COUNTY FORM FOUR JOINT EXAMINATION
Kenya Certificate of Secondary Education (K.C.S.E)
232/3
PHYSICS
PAPER 3
MARCH, 2015
TIME: 2 ½ HOURS.
Instructions:
o Write your name in the spares provided above
o Attempt all questions in the spaces provided
o You are to use 15 minutes of the 2 ½ hrs reading and confirming the apparatus provided
o Working must be clearly shown
o Non programmable silent calculator may be used
This paper consists of 8 printed pages.
Candidates should check the question paper to ascertain that all pages are printed as indicated
and that no question is missing.
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Question 1
Part A
You are provided with the following apparatus
•
a candle
•
a cross wire fixed on a screen
•
a wooden screen
•
a convex lens
•
a convex mirror
•
a metre rule -
•
2 lens/mirror holders.
proceed as follows;
a.
determine the focal length fi of the lens by focusing a distant object.
Fl………………………………..
b.
lmk
place the lens at a distance of x=30cmfrom the cross wire and move the screen A
until a sharp image of the cross wire is focused on it as shown in the diagram
below
c.
without moving lens and the screen A, place the convex mirror as shown in diagram above
and move it until a sharp image of the cross wire is formed on the screen next to the
crosswire.
d.
measure the distance d between the lens and the mirror and record on the table below
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Distance x of lens from crosswire(cm)
Distance y(cm)
Distance, d (cm)
y-d (cm)
30
40
3mks
e.
repeat procedure b to d for the value of x = 40cm
f.
calculate the mean value of y-d(cm)
g.
calculate the quantity f2 of the convex mirror from equation below.
F2 
lmk
mean of  y  d 
2
2mks
Part B
You are provided with the following apparatus
•
A triangular prism
•
A piece of soft card board
•
Four optical pins
•
A plain sheet of paper
•
Thumb pins
Proceed as follows;
a.
Place the plain sheet of paper on the soft board. Trace the triangular outline of the prism on the
sheet of paper. Remove the prism and use a ruler to extend the three sides of the outline
Use a protractor to measure the refracting angle R of the prism.
R = …………………………………………………………………………
b.
lmk
on the side AB of the triangular prism outline,draw a normal at a point halfway between A and B.
(this normal will be used for the rest of the experiment).
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c.
Draw a line at an angle i=300 to the normal. Stick two pins p1 and p2 vertically on this line see
figure below
d.
Place the prism accurately on the outline .By viewing through the prism from side AC. Stick two
pins p3 and p4 vertically such that they are in line with the images of pins p1 and p2
Remove the pins and the prism. Draw a line joining marks made by p3and p4. Extend this line to
meet AC. see figure below.
e,
Repeat the procedures in( c) and (d)above for other values of I as shown in the table below.
Complete the table.
Angle of incidence i
30
35
40
45
50
55
60
Angle 
Angle of emergence E = 90 - 
f.
i.
On the grid provided plot the graph of the angle of emergence E( y-axis) against the angle
of incidence I
ii.
5mks
use the graph to find I at which i=E
(forward the work sheet together with the answer script)
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Question 2
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You are provided with the following apparatus
•
100g masses(2)
•
A metre rule
•
2 pieces of thread
•
A beaker
•
A knife edge
•
A vernier caliper
•
Liquid I
Proceed as follows
a. Using the vernier caliper, determine the volume of the 100g mass provided.
b.
3mks
Arrange the apparatus as shown in the diagram below such that x=100mm from pivot (cog of
metre rule) with 100g mass completely immersed in the liquid I and hang the other mass from the
metre rule and adjust its position until the system is equilibrium
i.
Record the position of the cog……………………………………………
ii.
Determine the distance y in mm
Y = ………………………………………………………………………
iii.
given that
1mk
1mk
y wx

where Wx is the apparent weight of the mass in the liquid L and Wy, is
x wy
the actual weight Calculate the value of Wx and the up thrust U of the liquid
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c.
Arrange the apparatus as in the diagram such that x=5cm from the pivot. With the 100g mass
completely immersed in the liquid L, hang the other 100g mass on the metre rule and adjust its
position until the system is in equilibrium as shown in the diagram.
Repeat the procedure above with the following values of x and fill the table (ensure the pivot is
changed throughout the experiment)
x(cm)
5
10
15
20
25
30
y(cm)
d.
plot a graph of y against x 4mks
e.
determine the slope s of the graph 2mks
f.
given that s 
f
w
where f is the apparent weight of the mass in the liquid Land w is the action weight, calculate the
value of:
g.
i.
f
1mk
ii.
U
1mk
hence determine the density of liquid L
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