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 |
1-13 |
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 U-shaped 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 x108 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 N-pole and end at the S-pole
-
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 U-shaped 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=1/10-1/8
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/(40-10) =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)-
anw sin Ꝋ1 =ang Sin Ꝋ 2 Sin r = 1.33 sin 55/1.5
1.33 Sin 55 = 1.5 Sin r Sin r=0.7263
r=46.580
-
- 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)-
CT= +2 =2.4 + 2 =4.4µF
Q=CV
=4.4 X10-6X 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)
-
hi=3cm x 5 =15cm
-
- Image distance (2marks)
- V=7.5cm x 5 =37.5cm
- Magnification (2marks)
-
M =V/U OR M=HI/HO
=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 =(0.75-1.125)/(1.0-0.5)
=-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)-
RE = 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)
-
VS/VP =NS/NP
VS=400 X 120/1200
VS=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 x108 m/s). (2marks)
-
C=λf λ=C/f
=3.0 x 108/100x 103
=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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