PHYSICS
PAPER 3: PRACTICAL
QUESTION 1 (20 marks)
You are provided with the following
 A rectangular glass block.
 Four optical pins.
 Soft board.
 A plain paper.
 4 thumb tacks.
Proceed as follows:
 Place the glass block on the plain paper and trace it out using a pencil.
 Remove the glass block and construct a normal at B (a third of the outline from left edge) towards the edge as shown in the set up above.
 Construct an incident ray AB of an angle of incidence i equal to 15°. Fix two optical pins P_{1} and P_{2} along ray AB.
 Replace the glass block and trace the ray ABCD by locating Positions of P3 and P4 on the opposite side of the glass block such that P_{1}, P_{2}, P_{3} and P_{4} appear to lie on a straight line.
 Remove the glass block and draw the path of the ray ABCD using pencil.
 Measure length L (B to C) using a ruler and record it on the table below
 Complete the table below for the values i = 25°,35°,45° and 55°.
iº L(cm) L^{2}(cm^{2}) ^{1}/_{L²}(cm^{2}) Sin i Sin^{2}i 15 25 35 45 55  Plot a graph of ^{1}/_{L²}(y – axis) against Sin^{2} i (5mks)

 Determine slope S, from the graph (3mks)
 the intercept C, of the ^{1}/_{L} axis (1mk)
 Given that C= Sn^{2}, determine the value of constant n (Use the absolute value of S). (3mks)
 Complete the table below for the values i = 25°,35°,45° and 55°.
QUESTION 2 (20 marks)
PART A
You are provided with;
 A cell and a cell holder
 A resistance wire on millimeter scale
 Six connecting wires with crocodile clips eac
 An Ammeter (0 – 1 A)
 A voltmeter (0  3 V)
 A micrometer screw gauge
 A switch

 Measure diameter of the wire at two different points using micrometer screw gauge. (2mks)
d_{1}=
d_{2}=  Calculate the average diameter d, in metres. (2mks)
 Measure diameter of the wire at two different points using micrometer screw gauge. (2mks)
 Connect the cell, the ammeter and the 1.0 m length of resistance wire PQ in series.
 Measure the p.d (Vo) across 1.0 m length resistance wire and the current Io. (2mks)
V_{o} = …………..
I_{o} = ……………  Calculate the resistance of the wire Ro. (1mks)
Ro =  Calculate the crosssection area of the wire. (1mk)
A =π(^{d}/_{2})^{2}  Determine the value of quantity ρ of the wire given the relation ρ=(R_o A)/L where L is length of the wire PQ. (2mks)
 Measure the p.d (Vo) across 1.0 m length resistance wire and the current Io. (2mks)
PART B
Apparatus
 A metre rule
 One 50 g mass and one 100 g mass
 A stand with bosses
 Some water in a beaker
 Three threads
 Liquid L in a beaker, tissue paper
Procedure
 Balance the metre rule on the knife edge and record the reading at this point.
Balancing Point = ………………. (1mk)
(For the rest of the experiment the ruler must be balanced at this point)  Set the apparatus as shown in the figure below. Use the thread provided to hang the masses such that the positions of support can be adjusted.
 The balance is attained by adjusting the position of the 100 g mass. Note that the distance x and D are measured when the 50 g mass is fully submerged in water. Record X and D
X = …………………………………………………... cm. (1mk)
D = …………………………………………………... cm. (1mk)  Applying the principle of moments, determine the weight W1 of the 50 g mass in water and hence determine the upthrust Uw in water
W_{1} = …………………………………………………………….…N. (2mks)
U_{w} =……………………………………………………………… N. (1mk)  Remove the 50 g mass from the water and dry it using the tissue paper. Balance the metre rule when the mass of 50 g is fully submerged in the liquid L while maintaining distance D. Record the value of the distance X.
X = …………………………………………………….. cm. (1mk)  Apply the principle of moments to determine the weight W2 of the 50 g mass in the liquid L and hence determine the upthrust UL in the liquid.
W_{2} = ……………………………………………………………….. N. (1mk)
U_{L} = ………………………………………………………………… N. (1mk)  Determine the relative density R.D of the liquid, given that (1mks)
R.D=^{UL}/_{UW}
CONFIDENTIAL
QUESTION 1
 A rectangular glass block.
 Four optical pins.
 Soft board.
 A plain paper.
 4 thumb tacks.
 Ruler and protractor
QUESTION 2
 A metre rule.
 One 50 g mass and one 100 g mass
 A stand with bosses
 90 cm^{3} of water in a 100 ml beaker
 Three threads
 90 cm^{3} of paraffin labelled liquid L in a 100ml beaker
 Tissue paper
 A cell and a cell holder
 A resistance wire on millimeter scale
 Six connecting wires with crocodile clips each
 An Ammeter (0 – 1 A)
 A voltmeter (0  3 V)
 A micrometer screw gauge
 A switch
MARKING SCHEME
QUESTION 1 (20 marks)
You are provided with the following
 A rectangular glass block.
 Four optical pins.
 Soft board.
 A plain paper.
 4 thumb tacks.
Proceed as follows:
 Place the glass block on the plain paper and trace it out using a pencil.
 Remove the glass block and construct a normal at B (a third of the outline from left edge) towards the edge as shown in the set up above.
 Construct an incident ray AB of an angle of incidence i equal to 15°. Fix two optical pins P_{1} and P_{2} along ray AB.
 Replace the glass block and trace the ray ABCD by locating Positions of P3 and P4 on the opposite side of the glass block such that P_{1}, P_{2}, P_{3} and P_{4} appear to lie on a straight line.
 Remove the glass block and draw the path of the ray ABCD using pencil.
 Measure length L (B to C) using a ruler and record it on the table below
 Complete the table below for the values i = 25°,35°,45° and 55°.
iº L(cm) L^{2}(cm^{2}) ^{1}/_{L²}(cm^{2}) Sin i Sin^{2}i 15 6.5 42.25 0.02367 0.2588 0.06698 25 6.6 43.56 0.0230 0.4226 0.1786 35 6.9 47.61 0.02100 0.5736 0.3290 45 7.3 53.29 0.01877 0.7071 0.5 55 7.7 59.29 0.01687 0.8192 0.6710  All values to 1dp
Each correct value
(1mk up to max of 4
points(max 4mks)Correct conversion to
4sf or exact of all
values=1mkCorrect conversion to
4sf or exact of all
value= 1mkCorrect conversion
to 4sf or exact for
all values=1mkCorrect conversion
to 4sf or exact for
all values = 1mk  Plot a graph of ^{1}/_{L²}(y – axis) against Sin^{2} i (5mks)

 Determine slope S, from the graph (3mks)
S=(∆^{1}/_{L² })/∆Sin^{2}i
=0.0240.016cm^{2}
0.10.75=0.008 cm^{2}
0.65=0.012308 cm^{2 }
 the intercept C, of the ^{1}/_{L} axis (1mk)
C=0.012308 cm^{2 }
 Given that C= Sn^{2}, determine the value of constant n (Use the absolute value of S). (3mks)
n^{2}= 0.0252 cm^{2}
0.012308 cm^{2}=2.0475
n=1.4309
 Determine slope S, from the graph (3mks)
 Complete the table below for the values i = 25°,35°,45° and 55°.
QUESTION 2 (20 marks)
PART A
You are provided with;
 A cell and a cell holder
 A resistance wire on millimeter scale
 Six connecting wires with crocodile clips eac
 An Ammeter (0 – 1 A)
 A voltmeter (0  3 V)
 A micrometer screw gauge
 A switch

 Measure diameter of the wire at two different points using micrometer screw gauge. (2mks)
d_{1}= 0.29 mm (+ or – 0.02 mm)
d_{2}= 0.31 mm (+ or – 0.02 mm)  Calculate the average diameter d, in metres. (2mks)
d=d1+d2
2
=0.29+0.31 =0.30 mm
2
= 0.30 =0.00030 m
1000
 Measure diameter of the wire at two different points using micrometer screw gauge. (2mks)
 Connect the cell, the ammeter and the 1.0 m length of resistance wire PQ in series.
 Measure the p.d (Vo) across 1.0 m length resistance wire and the current Io. (2mks)
V_{o} = 0.81 V (+ or – 0.1 V)
I_{o} = 0.1 A (+ or – 0.02 A)  Calculate the resistance of the wire Ro. (1mks)
Ro = =^{0.81 V}/_{0.1 A}
=8.1 Ω  Calculate the crosssection area of the wire. (1mk)
A =π(^{d}/_{2})^{2}A =π0.0003^{2}
2
=7.069 ×10^{8} m^{2}  Determine the value of quantity ρ of the wire given the relation ρ=^{RoA}/_{L} where L is length of the wire PQ. (2mks)
ρ =8.1 Ω ×7.069 ×10^{8} m^{2}
1 m
ρ =5.726 ×10^{7} m
 Measure the p.d (Vo) across 1.0 m length resistance wire and the current Io. (2mks)
PART B
Apparatus
 A metre rule
 One 50 g mass and one 100 g mass
 A stand with bosses
 Some water in a beaker
 Three threads
 Liquid L in a beaker, tissue paper
Procedure
 Balance the metre rule on the knife edge and record the reading at this point.
Balancing Point = 50.2 cm (+ or 1 cm) (1mk)
(For the rest of the experiment the ruler must be balanced at this point)  Set the apparatus as shown in the figure below. Use the thread provided to hang the masses such that the positions of support can be adjusted.
 The balance is attained by adjusting the position of the 100 g mass. Note that the distance x and D are measured when the 50 g mass is fully submerged in water. Record X and D
X = 18.0 cm. (1mk)
D = 40.2 cm. (1mk)  Applying the principle of moments, determine the weight W1 of the 50 g mass in water and hence determine the upthrust Uw in water
W_{1} =sum of clockwise moments=sum of anticlockwise moments
U_{w} =
40.2 × W1 = 18 × 1
100 100
W1=^{18}/_{100} × 1 × ^{100}/_{40.2 }
W1=0.4478 NUw=Real weightApparent weight
Uw=0.5 N0.4478 N
=0.0522 N  Remove the 50 g mass from the water and dry it using the tissue paper. Balance the metre rule when the mass of 50 g is fully submerged in the liquid L while maintaining distance D. Record the value of the distance X.
X =X = 68.8 – 50.2
= 18.4 cm.  Apply the principle of moments to determine the weight W2 of the 50 g mass in the liquid L and hence determine the upthrust UL in the liquid.
W_{2} =sum of clockwise moments=sum of anticlockwise moments
^{40.2}/_{100} × W2 = ^{18.4}/_{100} × 1
U_{L} =
W2=^{18.4}/_{100} × 1 × ^{100}/_{40.2 }
W2=0.4577 NUw=0.5 N0.4577 N
=0.0423 N  Determine the relative density R.D of the liquid, given that (1mks)
R.D=^{UL}/_{UW}=^{0.0423}/_{0.0522}=0.8103
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