# Physics Paper 3 Questions and Answers - Catholic Diocese of Kakamega Mock Exams 2023

INSTRUCTIONS TO CANDIDATES

1. Write your Name and Index Number in the spaces provided above
2. Sign and write the date of examination in the spaces provided above
3. Candidates are advised to record their observations as from as they are made
4. Non-programmable silent electronic calculators may be used

QUESTION

You are provided with the following apparatus.

• Rectangular glass block
• Four optical pins
• Metre rule
• Protractor
• Soft board
• White plain paper
• Cellotape
• 4 thumb tacks
• Plane mirror

Proceed as follows:-

1.
1. Measure and record the breadth b of the glass block b =           cm (1mk)
2. Using cellotape, fix the mirror on one side (length) of the glass block and trace the outline on the plain paper.
3. Draw the normal NK to the side AB and measure angle i = 10° from the normal.
4. Draw the line representing the incident ray and fix pins P1 and P2 as shown in figure 1.
5. By observing the images of the pins P1 and P2 locate the positions P3 and P4 such that they appear in a line (no-parallax) using other pins.
6. Join the points P3 and P4 and extend them to intersect line P1 P2 produced. Measure the perpendicular distance Y.

7. Repeat the steps for different values of i and record your results in the table below.
Table
 i (º) 10 20 30 40 45 y (cm)
(5mks)
8. Plot a graph of y against i
(5mks)
9. Given that kyo = b where yo is the y-intercept determine the value of k
(2mks)
10. What is the significance of k
(1mk)
2.
3. Now remove the mirror, place the rectangular glass block on the plain paper and draw its outline again.
1. Remove the block and draw a perpendicular line NX on one of the longer sides as shown in figure 2
2. Draw an incident ray at angle of 30° to NX
3. Fix pins P1and P2 along the line for the incident ray then replace the block in its position.
4. By viewing through side AD, fix P3 and P4 in line with images of P1 and P2.
5. Remove the block and draw the line P3P4 to touch AD of the block. Join Y to X and  measure the angle of refraction r.
6. Record your results and complete the table
Table 2
 i (º) r (º) Sin i Sin r 30
(3mks)
7. Determine the value of t given that
Sin r =   1
2t
NOTE: Submit the white plain paper

QUESTION

SECTION

You are provided with the following

• A watch glass
• A small piece of plasticine
• Marble
• Stop watch
• Vernier calipers (To be shared)
• An electronic balance (To be shared)
Proceed as follows:-
1. Measure and record the mass of the marble m =                  g
(2mks)
2. Place the watch glass flat on the table with a small piece of plasticine to fix it firmly on  the bench at the one place it touches.
(1mk)
3. Release the marble from one end of the watch glass and time 5 complete oscillations with a stop watch
(1mk)
4. Repeat this three times
5. Fill the table below
 Time for 5 ocillations Periodic Time (s) 1 2 3
(3mks)
6. Find the average periodic time T(s)
(1mk)
7. Measure the diameter of the Marble with Vernier Calipers and hence find its radius.
Diameter d                    cm
(1mk)
(1mk)
8. Determine the volume of the Marble given that
V = 4/3 π r 3 where π = 3.142
(2mks)
9. Calculate the inner radius of curvature of the watch glass R from the formular (2mks)
R - r =   gT
4 π 2
where g = 10N/kg
π = 3.142 and
R is in metres.
10. Determine the density of the marble in SI units.

SECTION B

You are provided with the following:-

• Voltmeter (0-5v)
• 100cm bare nichrome wire fixed on a mm scale
• Micrometer screw gauge
• Two size D dry cells in a holder
• Connecting wires
Proceed as follows:-
1. Using a micrometer screwgauge, measure the Diameter of the nichrome wire.
D =                   mm
(1mrk)
2. Determine the cross sectional area A given that
A = 11D2 where D is in metres
14
(2mks)
3. Set up the apparatus as shown below

4. Measure the emf E of the cells where the jockey is not connected to Q
5. Connect the Jockey to Q (Length L = 100m) and record the value of V
V =                   V
(1mk)
6. Given that 1/v = rA/fLe + 1/E where r is the internal resistance of and f is the resistivity of the nichrome wire, determine the value of r if f = 1.0 x 10-6 Ωm
(2mks)

MARKING SCHEME
QUESTION 1

1.
1. b = 6.3 ± 0.2cm 1d.p
(1mk)
2. Diagram
(1/2mk )
3.  iº 10 20 30 40 50 Y (cm) 4.1 4 3.9 3.8 3.7
1 mark each
(5mks)
4. Graph
S-1
P-2
L-1
A-1
5
(5mks)
5. Ky0 = b
K =  b
y0
K = 6.3
4.2
K = 1.5 (1.4 - 1.6)
No Units
(1mk)
6. K is the refractive index of glass.
(1mk)

1. Diagram
(1⁄2 mk)
2.  iº Rº Sin i Sin r 30 18-21 0.5000 0.3256

No d.p 4s.f or exact
1mk each
(3mks)
3. Sin r = 1
2t
0.3256 =  1
2t
Rt =    1
0.3256
2t = 3.071

t = 3.071
2
t = 1.536
Substitution (1mk)
4s.f (1mk) or exact No units
(2mk)

QUESTION 2
SECTION A.

1. M = 5.0g ± 1.0 (1mk) 1 or 2 dip
(1mk)
2.  Time for S oscillations Periodic time T(s) 1 4.02 0.8040 2 4.04 0.8080 3 4.00 0.8000
Use student's value                                                               correct evaluation
2mk (2d.p)                                                                              4s.f or exact (1mk)
(3mks)
any two correct
3. Average T = 0.8040 +0.8080 +0.8000 (1⁄2 mk)
3
= 0.804 sec (12 mk) current units
4s.f or Exact
4. Diameter = 1.60 ± 0.01cm (1mk) 2d.p
correct evaluation
5. V = 4/3 π r3
4/3  x 3.142 x 0.0083 1mk
V = 6.435 x 10-6 m3 (1mk)
evaluation
(2mks)
6. R - r= gT2
4Π2
R-r=0.1637
R-0.8 = 0.1637 + 08
R = 0.9637m - (1mk) Use students' correct evaluation
4s.f or exact
Units a must.
7. Density =  mass
volume
5.0 x 10-3      correct substitution using students values
6.435x10-6    correct evaluation Units a must
= 777 kg/m3

SECTION B

1. D = 0.36 ± 0.01mm 2d.p
(1mk)
2. A = 11D 2
14
A = 11 x (3.6 x10-4)-2  (1mk)    substitution
14
A = 1.018 x 10-7 m2 (1mk)   correct Evaluation
units a must
3. E = 3.1 ± 0.1 V   (1mk)  1 d.p
4. V (2.0 - 2.8) V  (1mk)  1 d.p
5. 1  =  rA    +
v      fLe         E
1/2 =     1.018 x 10-7xr        (1mk) correct
1.0 x 10-6 x 1 x 3.0         3.0
1/2 = (0.0339)r + 0.3333    substitution
0.339r = 0.167              4s.f or exact
R = 4.926Ω  (1mk)           unit is a must
Use student's evaluation

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