INSTRUCTIONS TO CANDIDATES
 Answer all the questions in sections A and B
 Non programmable silent electronic calculators may be used.
FOR EXAMINER’S USE ONLY.
SECTION 
QUESTION 
MAXIMUM SCORE 
CANDIDATE’S SCORE 
A 
113 
25 

B 
14 
10 

15 
12 

16 
11 

17 
12 

18 
10 

TOTAL 
80 
QUESTIONS
SECTION A (25MARKS)
 A ray of light is incident on a plane mirror as shown in the figure below.
If the mirror is rotated anticlockwise through angle of 8o what will be the angle of rotation of the reflected ray? (1mark)  State two uses of a charged gold leaf electroscope (2marks)
 The table below shows part of the electromagnetic spectrum in order of decreasing wavelength.
A
B
Infrared
RadiationVisible
LightC
D
 Name the radiation C (1mk)
 Give one use of the wave D in medicine (1mark)
 A current of 0.5A flows in a circuit. Calculate the amount of charge that crosses a point in the circuit in 4 minutes. (2marks)
 Give two properties of magnetic field lines around a bar magnet. (2marks)
 The diagram below shows a displacement position graph for a slinky spring as it is continually vibrated at one end.
What is the Amplitude of the displacement? (1mark)
 Wavelength of the waves (1mark)
 The critical angle for a ray travelling from glass to air is 42 o. Determine the refractive index of the glass. (2marks)
 The diagram below shows a current – carrying wire wound on a Ushaped soft iron.
Draw the magnetic field patterns at P and Q (2marks)  An electrical heater rated 240V, 3000W is to be connected to a 240V mains supply through a 10 A fuse. Determine whether the fuse is suitable or not. (3marks)
 State one cause of power loss in long distance transmission wire and how this loss can be minimized. (1mark)
 Explain why walls of the studio are padded with woolen materials. (1mark)
 An object is placed 8cm from a concave mirror whose radius of curvature is 20cm. Determine the position of the image. (3marks)
 The figure below shows a pair of parallel plates of a capacitor connected to battery. The upper plate is displaced slight to the left.
State with a reason the effect of this movement on the capacitance. (2marks)
SECTION B (55 MARKS )

 Define the term critical angle. (1mark)
 The figure below shows an object O at the bottom of a beaker full of a liquid. An observer above the beaker sees its image at point X inside a liquid
Determine the refractive index of the liquid (3marks)  The diagram below shows a ray of light travelling from water to glass. Given that the refractive index of water and glass are 1.33 and 1.5 respectively.
Find the angle of refraction r in the glass (3marks)  The diagram below shows a simple network of capacitor.
If the potential difference between X and Y is 6V, calculate the total charge stored by the capacitors. (3marks)

 Define the term principal focus of a convex lens (1mark)
 State two characteristics of image formed by the diverging lens. (2marks)
 An object of height 10cm is placed 25cm from a converging lens of focal length 15cm.
 On the grid provided draw a ray diagram to locate the position of the image. (3marks)
 From the graph determine the;
 Image height (2marks)
 Image distance (2marks)
 Magnification (2marks)
 On the grid provided draw a ray diagram to locate the position of the image. (3marks)

 what is meant by electromotive force E.m.f of a cell (1mark)
 Name one factor that affect resistance of a metallic conductor. (1mark)
 In an experiment to determine E.m.f ,E and the internal resistance r of a cell, a student obtained the values of voltage V and current I . He then plotted the graph of voltage V against current below.
 Sketch the circuit that could be used to obtained the plotted results. (2marks)
 Given that V=E – Ir determine
 E.m.f, E of the battery (2marks)
 Internal resistance r of the battery (2marks)
 What causes electrical resistance in conductors (1mark)
 The combined resistance of the resistors in the circuit below is 8Ω.
Find the value of R (2marks)

 State the Lenz’s law of electromagnetic induction (1mark)
 In the figure below show the direction of the induced current in the circuit (1mk)
 Give two factors that determine the magnitude of emf induced in a coil. (2marks)
 A transformer has 1200 turns in the primary circuit and 120 turns in the secondary circuit has its primary circuit connected to a 400V a.c source.
 Name the type of the transformer. (1mark)
 Determine the secondary voltage (2marks)
 Determine the efficiency of the transformer given that the current in the primary coil is 0.10A and in the secondary coil is 0.80A (3marks)
 One of the primary ways in which power is lost in a transformer is through eddy currents. State how eddy currents can be minimized (1mark)
 State one property of soft iron that makes it suitable for use as a transformer core. (1mark)

 Give two conditions neccessary for the formation of stationary waves (2marks)
 The figure below shows progressive wave crossing from a deep to shallow region.
 On the diagram show how the waves proceed in the shallow region. (1mk)
 State the property of the waves illustrated in the diagram you have drawn above in b(i) (1mark)
 Calculate the wavelength of a radio wave of frequency 100 kHz (Take C=3.0 x10^{8} m/s). (2marks)
 The diagram below shows light rays from two coherent sources S1 and S2 falling on the screen. Dark and bright fridges are observed between M and N.
Explain how Bright fridges are formed (1mark)
 Dark fridges are formed (1mark)
 State and explain what is observed when light of a higher frequency is used (2marks)
MARKING SCHEME
SECTION A (25MARKS)
 A ray of light is incident on a plane mirror as shown in the figure below.
If the mirror is rotated anticlockwise through angle of 8º what will be the angle of rotation of the reflected ray? (1mark)
Angle of rotation of the reflected ray=angle of rotation X 2
= 8X2 =16 ^{o}

 State two uses of a charged gold leaf electroscope (2marks)

To identify type of charge

To identify conductors and insulators.

 The table below shows part of the electromagnetic spectrum in order of decreasing wavelength.
A
B
Infrared
RadiationVisible
LightC
D
 Name the radiation C (1mk)

U.V Radiation

 Give one use of the wave D in medicine (1mark)

Radiography

Cancer therapy

 Name the radiation C (1mk)
 A current of 0.5A flows in a circuit. Calculate the amount of charge that crosses a point in the circuit in 4 minutes. (2marks)

Q=It
=0.5X4X60=120C

 Give two properties of magnetic field lines around a bar magnet. (2marks)

Originate from Npole and end at the Spole

The field lines do not intersect.

 The diagram below shows a displacement position graph for a slinky spring as it is continually vibrated at one end.
What is the Amplitude of the displacement? (1mark)

20cm

 Wavelength of the waves (1mark)

60cm

 Amplitude of the displacement? (1mark)
 The critical angle for a ray travelling from glass to air is 42 o. Determine the refractive index of the glass. (2marks)
 n=1/sin C n=1/sin42 =1.494
 The diagram below shows a current – carrying wire wound on a Ushaped soft iron.
Draw the magnetic field patterns at P and Q (2marks)  An electrical heater rated 240V, 3000W is to be connected to a 240V mains supply through a 10 A fuse. Determine whether the fuse is suitable or not. (3marks)

1=P/V =3000/240 =12.5A fuse not suitable since 12.5 > 10A

 State one cause of power loss in long distance transmission wire and how this loss can be minimized. (1mark)

High resistance in cables – use thicker cables to reduce resistance

High current I in the cables stepping up the voltage before transmission.

 Explain why walls of the studio are padded with woolen materials. (1mark)

To absorb incident sound waves preventing the formation of echo.

 An object is placed 8cm from a concave mirror whose radius of curvature is 20cm. Determine the position of the image. (3marks)

1/f=1/U+1/V 1/V=1/101/8
1/10=1/8+1/V 1/V=2/80 V=40cm

 The figure below shows a pair of parallel plates of a capacitor connected to battery. The upper plate is displaced slight to the left.
State with a reason the effect of this movement on the capacitance. (2marks)
Area of overlap decreases hence causing decrease in capacitance

SECTION B (55 MARKS )

 Define the term critical angle. (1mark)

The angle of incidence in the optically denser medium for which the angle of refraction in the less dense medium is 90^{ o}

 The figure below shows an object O at the bottom of a beaker full of a liquid. An observer above the beaker sees its image at point X inside a liquid
Determine the refractive index of the liquid (3marks)
n=real depth /apparent depth =40/(4010) =1.333

 The diagram below shows a ray of light travelling from water to glass. Given that the refractive index of water and glass are 1.33 and 1.5 respectively.
Find the angle of refraction r in the glass (3marks)
_{a}n_{w} sin Ꝋ_{1} =_{a}n_{g} Sin Ꝋ_{ 2} Sin r = 1.33 sin 55/1.5
1.33 Sin 55 = 1.5 Sin r Sin r=0.7263
r=46.58^{0}

 The diagram below shows a simple network of capacitor.
If the potential difference between X and Y is 6V, calculate the total charge stored by the capacitors. (3marks)
C_{T}= +2 =2.4 + 2 =4.4µF _{ }Q=CV
=4.4 X10^{6}X 6
=26.4 µC

 Define the term critical angle. (1mark)

 Define the term principal focus of a convex lens (1mark)

Point on the principal axis where rays parallel and close to the principal axis converge after refraction by the lens.

 State two characteristics of image formed by the diverging lens. (2marks)

Virtual upright/erect
Diminished

 An object of height 10cm is placed 25cm from a converging lens of focal length 15cm.
 On the grid provided draw a ray diagram to locate the position of the image. (3marks)
 From the graph determine the;
 Image height (2marks)

h_{i}=3cm x 5 =15cm

 Image distance (2marks)
 V=7.5cm x 5 =37.5cm
 Magnification (2marks)

M =V/U OR M=H_{I}/H_{O}=37.5/25 =15/10
=1.5 =1.5

 Image height (2marks)
 On the grid provided draw a ray diagram to locate the position of the image. (3marks)
 Define the term principal focus of a convex lens (1mark)

 what is meant by electromotive force E.m.f of a cell (1mark)

This is the total voltage across the terminals of a cell in an open circuit.

 Name one factor that affect resistance of a metallic conductor. (1mark)
 length ,thickness of the conductor,temperature.
 In an experiment to determine E.m.f ,E and the internal resistance r of a cell, a student obtained the values of voltage V and current I . He then plotted the graph of voltage V against current below.
 Sketch the circuit that could be used to obtained the plotted results. (2marks)
 Given that V=E – Ir determine
 E.m.f, E of the battery (2marks)

Extrapolate

Emf E =1.5V

 Internal resistance r of the battery (2marks)

r = slope =(0.751.125)/(1.00.5)
=0.375/0.5
=0.75
r=0.75Ω

 E.m.f, E of the battery (2marks)
 Sketch the circuit that could be used to obtained the plotted results. (2marks)
 What causes electrical resistance in conductors (1mark)

The collisions between the charge/electrons flowing and atoms or impurities in the conductor.

 The combined resistance of the resistors in the circuit below is 8Ω.
Find the value of R (2marks)
R_{E} = R1R2 / R1+ R2 8= 12 x R / 12 + R 96+8R=12R 4R=96 R =24Ω

 what is meant by electromotive force E.m.f of a cell (1mark)

 State the Lenz’s law of electromagnetic induction (1mark)

The direction of induced emf is such that the current which it causes to flow produces a magnetic effect that opposes the change producing it.

 In the figure below show the direction of the induced current in the circuit (1mk)
 Give two factors that determine the magnitude of emf induced in a coil. (2marks)

Rate of change of magnetic flux

Number of turns in the coil

 A transformer has 1200 turns in the primary circuit and 120 turns in the secondary circuit has its primary circuit connected to a 400V a.c source.
 Name the type of the transformer. (1mark)

Step down transformer

 Determine the secondary voltage (2marks)

V_{S}/V_{P} =N_{S}/N_{P}
V_{S}=400 X 120/1200
V_{S}=40V

 Determine the efficiency of the transformer given that the current in the primary coil is 0.10A and in the secondary coil is 0.80A (3marks)

Efficiency= power output / power input x100%
= (40 x 0.8) / )400 x 0.1) x 100%
= 32/40 x100% =80%

 One of the primary ways in which power is lost in a transformer is through eddy currents. State how eddy currents can be minimized (1mark)

Core is made of laminated sheets

 State one property of soft iron that makes it suitable for use as a transformer core. (1mark)

Iron is easily magnetized and demagnetized

 Name the type of the transformer. (1mark)
 State the Lenz’s law of electromagnetic induction (1mark)

 Give two conditions neccessary for the formation of stationary waves (2marks)

Same speed

Same frequency

Same amplitude (NB:Deny nearly equal Amplitude)

 The figure below shows progressive wave crossing from a deep to shallow region.
 On the diagram show how the waves proceed in the shallow region. (1mk)
 State the property of the waves illustrated in the diagram you have drawn above in b(i) (1mark)
 Refraction
 Calculate the wavelength of a radio wave of frequency 100 kHz (Take C=3.0 x10^{8} m/s). (2marks)

C=λf λ=C/f
=3.0 x 10^{8}/100x 10^{3}=3000m

 The diagram below shows light rays from two coherent sources S1 and S2 falling on the screen. Dark and bright fridges are observed between M and N.
Explain how Bright fridges are formed (1mark)

They are formed as a result of constructive interference of the two waves from the two sources

 Dark fridges are formed (1mark)

They are formed as a result of destructive interference of the waves from the two sources.

 State and explain what is observed when light of a higher frequency is used (2marks)

The bright and dark fridges become more closely spaced.This is because increase in frequency causes decrease in wavelength, hence it takes shorter intervals of distance for the path difference.

 Bright fridges are formed (1mark)
 Give two conditions neccessary for the formation of stationary waves (2marks)
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