Free KCSE Physics Topical Questions KNEC Standards

Define Radio-activity

21/10/2021

(a) Define Radio-activity (2mks)

Radioactivity is the spontaneous disintegration of a nucleus releasing
alpha, beta and gamma radiations accompanied by the release of energy

(b) When carrying out experiments with radioactive substances the source should never be held with bare hands but with forceps. Explain? (1mk)

Radioactive substances are harmful to body cells when ingested

(i) Plot on the graph paper provided the graph of the count rate (y-axis) against time

A graph of count Rate against time(s)

(ii) From the graph, determine the half-life of Radon-220 (1mk)

Half-life of radon 220=54 sec + 2 (showing on graph a must)

(e) The diagram in the figure below shows paths taken by three radiations A,B and C from a radioactive isotope through an electric field.

(i) State the charge on plate Y (1mk)

Negative

(ii) Identify the radiations A and C (2mks)

A- Beta particles
B-Alpha particles

(iii) Give a reason why C deviates more than A (1mk)

C more massive than A

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A 240v mains transformer has 800 turns in the primary and N turns in the secondary. It is used to supply energy to a 12v/21w lamp

21/10/2021

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(a) A 240v mains transformer has 800 turns in the primary and N turns in the secondary. It is used to supply energy to a 12v/21w lamp.

(i) Calculate the number of turns in the secondary (2mks)

(ii) What is the efficiency of the transformer if the current drawn from the 240V mains is 100mA (2mks)

The circuit above shows a step-down transformer used to light a lamp of resistance.

Calculate.

(i) the reading of voltmeter, V, with, S, open (2mks)

(ii) the reading of the ammeter A with S closed (neglect the effective resistance of the secondary winding) (2mks)

(iii) the power dissipated in the lamp (2mks)

(iv) the primary current if the transformer is 90% efficient (3mks)

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State two advantages of a C.R.O as a voltmeter

21/10/2021

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(a) State two advantages of a C.R.O as a voltmeter

Measures both D.C and A.C (1mk)

Its accurate and does not take any current (1mk)

(b) A television tube is a cathode ray tube modified. State two modifications

Presence of magnetic coils
Incoming signal from the aerial is fed into the grid

(c) State the functions of the following parts of a C.R.O

(i) Grid

Grid controls brightness of the spot

(ii) X-plates

horizontal displacement
time base control

(iii) Fluorescent screen

Identify the position of the electron beam

(d) A modern X-ray tube is shown below

(i) Name the parts labeled A-D (2mks)

A

Copper Anode

B

Tungsten Target

C

Filament

D

Cooling fins

(ii) Give the functions of:- (1mk)

(i) Shielding with lead

Lead absorbs the radiation (1mk)

(ii) Evacuating the tube

Prevents collisions, avoid secondary electrons (1mk)

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Distinguish between a p-type and n-type semi conductors

21/10/2021

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(a) Define doping (1mk)

Process of introducing foreign element (impurity) into a pure semi-conductor,

(b) Distinguish between a p-type and n-type semi conductors (2mks)

(c) Using a diagram illustrate a forward P-N junction (2mks)

(d) The figure below shows a bridge circuit

A capacitor has been connected across the resistor as shown

(i) Sketch of the figure below the wave form when a CRO is connected across the resistor, R

(ii) On the same axes, sketch a wave form when C.R.O is connected across R when the capacitor has been removed (1mk)

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Explain why bulbs in along corridor are not wired in series

21/10/2021

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(a) Explain why bulbs in along corridor are not wired in series (2mks)

High resistance, dim light
When one goes off, all others go off

(b) An electric cooker has an oven rated 2500w, a grill rated 1500w and two plates each of 1000W. This cooker operates directly from 240v supply. What is the costs of operating all the parts at once for 30 minutes if electricity costs sh.10.00 per unit? (3mks)

(c) Study the figure below

(i) What name is given to the fitting in the diagram (1mk)

3 pin plug

(ii) Identify the parts labeled (2mks)

A

Neutral wire

B

Earth wire

C

Live wire

D

Fuse

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The diagram in the figure below represents a wheel and axle used as a machine, whose efficiency is 80% to raise 400N of building materials. The wheel and axles have diameters of 75cm and 15cm respectively.

19/10/2021

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(a) The diagram in the figure below represents a wheel and axle used as a machine, whose efficiency is 80% to raise 400N of building materials. The wheel and axles have diameters of 75cm and 15cm respectively.

The diagram in the figure below represents a wheel and axle used as a machine, whose efficiency is 80% to raise 400N of building materials. The wheel and axles have diameters of 75cm and 15cm respectively.

(i) Mark on the diagram the correct position and direction of the load to be lifted (1mk)

(ii) Name the principle on which this machine works (1mk)

The principle of moments

(iii) Calculate the effort needed to raise the load (3mks)

(iv) The machine is operated manually and raises the load to a height of 5m in 20 seconds. Calculate the power developed by the operator (2mks)

(b)
(i) State two factors that determines the efficiency of an inclined plane as a machine (2mks)

Smoothness of plane
angle of inclination

(ii) Explain how these factors affect efficiency (2mks)

Smoothness: Efficiency increases with smoothness since loses due to friction and minimized
Angle –efficiency increases with the angle of inclination since normal reaction decreases and so does friction.

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Explain what you understand by each of the following terms

19/10/2021

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Explain what you understand by each of the following terms:

(i) Angular velocity (1mk)

The angle covered in radians per second by an object in circular motion

(ii) Centripetal force (1mk)

The force that keeps an object in circular motion

b) A bicycle wheel with radius 28cm moves with a linear velocity of 8m/s, determine

(i) the angular velocity of the wheel (2mks)

(ii) the centripetal acceleration of a point on the rim of the wheel (2mks)

(c) To determine the relationship between angular velocity w and tension T, a student used a smooth disc with a hole at the centre, a string and cylindrical object of mass m, as shown below

To determine the relationship between angular velocity w and tension T, a student used a smooth disc with a hole at the centre, a string and cylindrical object of mass m, as shown above

Describe how the student went about determining the relationship, specifying any other necessary material or instrument not shown in the diagram (3mks)

The cylindrical mass was attached to a known weight, T, hanging freely below the hole. The disc was rotated with an increasing angular velocity w, till the hanging weight was steady. The experiment was repeated to obtain other values of w and their corresponding hanging weights

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A student set-up the apparatus as shown below to determine the power of an electric heater.

19/10/2021

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A student set-up the apparatus as shown below to determine the power of an electric heater

A student set-up the apparatus as shown above to determine the power of an electric heater

(a)
(i) Other than time, state the measurements that would be used to determine the quantity of heat P absorbed by ice in a unit time (2mks)

Current, voltage (p.d) mass of water collected temperature of the melt

(ii) Complete the circuit to show the connection of the essential circuit components (2mks)

(iii) Describe how the student would proceed to determine P (3mks)

Switch on the current and start the clock simultaneously
Record the steady venus current I and P.d.v
Note the temperature of the melt( should be 0oC)
Weighs the melt to obtain its mass m, collected over a known length of time , t

Apply Ivt=mlf

(iv) Give a reason why P may not be equal to the value indicated by the manufacturer (1mk)

It may not be operating at its optimum conditions of p.d and temperature, T. the heater also absorbs heat

(b) In another experiment, 100g of hot water at 90^oC was mixed with 20g of ice at 0^oC in a lagged plastics colorimeter. After stirring, all the ice melted and the temperature of the mixture was found to be 61.5^oC. Determine the latent heat of fusion of ice (3mks)

(Specific heat capacity of water = 4200Jkg^-1k^-1)

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The readings tabulated below shows how the length of a helical spring varied with the load hanging on it

18/10/2021

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The readings tabulated below shows how the length of a helical spring varied with the load hanging on it

(a)
(i) Complete the table to show the values of extension (2mks)

0,4.5,9.2,13.8,18.5,23.2 cm

(ii) Draw a graph of extension (y-axis) against load for the spring (5mks)

Graph

Labeling of axes
Straight line
Location of points
Scale used

(ii) Determining form the graph the proportionality constant of the spring (2mks)

(b) Two springs Q and R have proportionality constants 20N/M and 25N/M respectively. Q weighs 0.2 N while the weight of R is negligible. The two springs are arranged to support a load of 3.0N as shown in the diagram below

Determine the extension in
(i) Q……………………………………………..(1mk)

ii) R ……………………………………………(1mk)

(c) State two factors that determine the proportionality constant of a helical spring (2mks)

Diameter of spring, length of the spring/thickness of the wire coiled to make the spring
Diameter of wire used

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The diagram below shows two trolleys, A and B connected to each other by an elastic strip of negligible mass. The trolleys are pulled apart on a smooth plane till tension in the elastic strip is 4.0N and are then released suddenly

18/10/2021

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The diagram below shows two trolleys, A and B connected to each other by an elastic strip of negligible mass. The trolleys are pulled apart on a smooth plane till tension in the elastic strip is 4.0N and are then released suddenly

(a) State with reason the total momentum of the trolleys when they are just released (2mks)

Zero (0) –It is because their velocities are still zero/ They are still stationary

(b) Calculate the initial acceleration of trolley A when released (3mks)

(c) The velocity of the trolley B is 0.9ms^-1 just before it collides with A. Determine the velocity of A just before the collision

(d) Which trolley covers a longer distance before collision? Explain (2mks)

trolley A, because of it moves with high velocity

(e) Explain why the elastic strip may not stretch to the same original length after impact (2mks)

Friction force

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K.C.S.E Physics Q & A - MODEL 2019PP2QN19

15/10/2020

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K.C.S.E Physics Q & A - MODEL 2019PP2QN19

(a) Define half life as used in radioactivity.
(b) Figure 13 shows a device used to detect radioactivity by forming tracks when air is ionised.

(i) State the name of the device shown.
(ii) State how air in the device gets ionised.
(iii) Describe how tracks are formed
(c) (i) State two factors that determine the speed of the photoelectrons emitted from a metal surface
(ii) The energy of a photon of light is 2.21 eV. (electronic charge is 1.6x10^-19C and planks constant h is 6.63x10^-34Js)
I. Express this energy in joules.
II. Determine the frequency of the light that produces the photon.

answers

(a) Half life is the time taken for half the number of nuclides initially present in a sample to decay
(b). (ii) Expansion closed chamber
(ii) Due to collisions between the molecules from the radiations source and the air molecules
(iii) When the piston is pulled down air expands hence cools.
(c)(i) The work function of the metal
Energy of incident radiation frequency/wavelength

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K.C.S.E Physics Q & A - MODEL 2019PP1QN18

31/7/2020

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K.C.S.E Physics Q & A - MODEL 2019PP1QN18

(a) Figure 9 shows a graph of pressure against temperature for a fixed mass of gas at constant volume.

From the graph, determine the values of n arid e given that P = nT + c where n and c are constants.
(b) Explain why it is not possible to obtain zero pressure of a gas in real life situation.
(c) A fixed mass of a gas occupies 1.5 X 10^-3 m^-3 at a pressure of 760 mmHg and a temperature of 273 K. Determine the volume the gas will occupy at a temperature of 290K and a pressure of 720 mmHg.
(d) State any three assumptions made in kinetic theory of gases.

answers

(b) It is not possible to reduce the pressure of a gas to zero since by then most of the temperatures are very low hence the gas liquefies.

(d) Assumptions of the kinetic theory of gases:
Attraction of between the molecules is negligible.
Volume of the molecule is negligible compared to the volume of the container occupied by the gas.
The molecules undergo elastic collisions.
The length of time of a collision is negligible compared to the time between collisions.

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K.C.S.E Physics Q & A - MODEL 2019PP1QN17

31/7/2020

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K.C.S.E Physics Q & A - MODEL 2019PP1QN17

(a) State what ¡s meant by Brownian Motion.
(b) Figure 8 shows the graph of velocity against time For a small steel ball Falling in a viscous liquid.

(a) State what ¡s meant by Brownian Motion. (1 mark) (b) Figure 8 shows the graph of velocity against time For a small steel ball Falling in a viscous liquid. (i) Describe the motion of the steel ball as represented by part OA (ii) Explain why the velocity of A and B is constant (c)A student throws a tennis ball vertically upwards from the ground and it lands back after 8 seconds.( acceleration due to gravity g =10ms-2) Determine the: (i) maximum height reached by the ball iii) velocity with which the ball hits the ground. (3 marks)

(i) Describe the motion of the steel ball as represented by part OA
(ii) Explain why the velocity of A and B is constant
(c)A student throws a tennis ball vertically upwards from the ground and it lands back after 8 seconds.( acceleration due to gravity g =10m/s2)
Determine the:
(i) maximum height reached by the ball
iii) velocity with which the ball hits the ground.

answers

(a) Continuous random motion of particles.
(b) (i) It accelerates, velocity increases.
(ii) As the ball falls through the fluid, the Viscous drag increases until the sum of the Viscous drag and the upthrust becomes equal the weight of the steel ball, hence the resultant force becomes zero.

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K.C.S.E Physics Q & A - MODEL 2019PP1QN16

31/7/2020

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K.C.S.E Physics Q & A - MODEL 2019PP1QN16

(a) State the meaning of the term “heat capacity.”
(b) State how pressure affects the melting point of a substance.
(c)Figure 7 shows a set tip of apparatus that may be used to apparatus the specific latent heat of vaporization of steam

(I) Describe how the mass of condensed steam is determined.
(ii) Other than mass and time, state two other measurements that should be taken during the experiment.
(iii) Show how the measurements in (c)(ii) can be used to determine the specific latent heat of vaporization of water.
(iv) State the precaution that should be taken so that the mass of the condensed steam measured corresponds to the actual mass of steam collected during the time recorded in the experiment
(v) State why it is not necessary to measure temperature in in the set up

answers

(a) Heat capacity is the quantity of heat energy required to raise the temperature of a substance by 1K.
(b) - Increase in pressure lowers the melting point while decrease in (1 mark) pressure raises/increases the melting point.
(c) (i) - Measure the mass of the empty beaker M1.
Measure the mass of the beaker plus the condensed steam M2
Get the difference between the two masses (M2 —M1) = M
(ii) - Voltage
Current

(iv) - Start timing when the steam drops start forming out steadily and Stop immediately the beaker is withdrawn.
(V) Steam is produced at boiling point where temperature is constant.

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K.C.S.E Physics Q & A - MODEL 2019PP1QN15

31/7/2020

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K.C.S.E Physics Q & A - MODEL 2019PP1QN15

(a)Figure 6 shows n bottle top opener being used to open a bottle.

Indicate on the diagram the direction of the load and the effort.
(b) State two ways ¡n which an inclined plane can be made to reduce the applied effort when pulling a Load along the plane.
(c) A block and tackle system has three pulleys in the upper fixed block and two pulleys in the lower movable block.
(i) Draw a diagram to show how the system can be set up in order to lift a load arid indicate the position of the load and effort.
(ii) State the velocity ratio of the set up.
(iii) In such a block and tackle system an effort of 200N is required to lift a load of 600N. Determine its efficiency

answers

(b)Reducing the angle of inclination.
Reducing the friction — using rollers, lubricants etc.

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K.C.S.E Physics Q & A - MODEL 2019PP1QN14

31/7/2020

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K.C.S.E Physics Q & A - MODEL 2019PP1QN14

(a) A student is provided with five 20g masses, a meter rule, a spring with a pointer, a stand a boss and a clamp.
(i) In the space provided, sketch a labelled diagram of the set up that may be used in order to verify Hooke’s law using these apparatus.
(ii) State two measurements that should be recorded in order to plot a suitable graph so as to verify Hooke’s law.
(iii) Describe how the measurements made in (ii) can be used to determine the spring constant.

(b) A helical spring stretches by 0.6cm when Supporting a weight of 40 g. Determine the extension when the same spring Supports a weight of 65 g.

answers

(ii) Force due to total mass hung.
Extension produced by hanging masses.
(iii) — Plot a graph of force against extension.
Determines the slope of the graph

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K.C.S.E Physics Q & A - MODEL 2019PP2QN18

31/7/2020

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K.C.S.E Physics Q & A - MODEL 2019PP2QN18

(ii) Describe how a magnet can be demagnetised using the electrical method.
(b) You are provided with two iron bars P and Q. One of the bars is magnetized while the other is not. Explain how themagnetized bar can be identified without using a magnet or magnetic material.
(c)Figure 12 shows two identical copper coils X and Y placed close to each other. Coil X is connected to a DC power supply while coil Y is connected to a galvanometer.

Explain what is observed on the galvanometer When the Switch is closed.
(ii) State What is observed on the galvanometer when the switch is opened.
(iii) State what wou1d be observed if the number of turns in coil Y is doubled.

answers

(a) Place the bar magnet inside a solenoid placed in the an East-West direction then pass an alternating current through the solenoid
(b) Suspend each of the bars through its center of gravity and set it swinging in a horizontal plane shows a vertical axis through its centre
The magnetized bar will always come to rest in a north-south direction
(c) (i) The galvanometer pointer first deflects then moves back when the switch is closed a current builds up in a coil X and due to change influx linkage an emf is induced in coil Y making an induced current to flow through the galvanometer during the time current in coil X is rising. When current through coil X is steady no induced current flows through the galvanometer since there is no change in flux linkage
Therefore pointer deflects back
(ii) Pointer deflects in the opposite direction.
(iii) Magnitude of deflection increases

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K.C.S.E Physics Q & A - MODEL 2019PP2QN17

31/7/2020

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K.C.S.E Physics Q & A - MODEL 2019PP2QN17

(a) Figure 10 shows a ray of light travelling from glass to air.

Determine the:
(i) critical angle of the glass — air interface
(ii) refractive index of glass
(b) Apiece of metal is embedded at the centre of an ice block 15cm from the surface of the ice. Given that the refractive index of ice is 1.32, determine how far from the surface of the ice block the metal appears to be.
(c) Figure 11 shows, two rays of incident on a diverging lens.

Complete the ray diagram to show the path of the rays after passing through the lens.
(d) (i) State two differences between the human eye and a camera lens.
(ii) State the name of the part of the eye that enable the lens to focus images of objects at different distances.

ANSWERS

(d)(i) Eye has a variable focal length whole the focal length of camera lens is fixed
Image distance from the lens is almost constant in the eye while in a camera it can be varied
Eye lens is muscle while glass/clear plastic
(ii) Ciliary muscles

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K.C.S.E Physics Q & A - MODEL 2019PP2QN16

31/7/2020

2 Comments

K.C.S.E Physics Q & A - MODEL 2019PP2QN16

(a) Define the following terms as used in waves:
(I) Amplitude
(ii) Wavelength
(b) Figure 8 shows water waves approaching a straight reflector at a speed of 40 cm/s.

(I) Draw on the diagram the reflected waves.
(ii) Given that the distance between the source and the reflector is 15 cm determine:
I. the wavelength of the waves
II. the frequency of the waves
(c) Figure 9 Shows light rays from two coherent sources S1 and S2 falling on a screen.
Dark and bright fringes are observed between A and B

(i) State how:
I. bright fringes are formed
II. dark fringes are formed
(ii) State what is observed when light of a higher frequency is used.

ANSWERS

(a)(i)Amplitude is the maximum displacement of a particle from the mean position
(ii)Wavelength is the distance between two successive points in a wave which are in phase
OR
Distance between two successive crests or troughs in a transverse
Wave/between rarefaction or compressions in a longitudinal wave.

(c)(I) due to constructive interference
(II) due to destructive interference
(ii) The fringes get closer
OR
When the frequency is higher the wavelength reduces hence the fringe separation decreases

2 Comments

K.C.S.E Physics Q & A - MODEL 2018PP2QN19

29/7/2020

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K.C.S.E Physics Q & A - MODEL 2018PP2QN19

Figure 8 shows two waves of nearly equal frequency produced simultaneously.

On the space provided, sketch the resultant of the two waves (beats).
(b) Figure 9(a) and 9(b) show barriers placed in the path of plane waves.

On each figure, sketch the pattern of waves after they pass the barrier.
(c) Figure 10 shows a displacement—distance graph for a certain wave motion.

(i) Indicate on the figure with letters A and B any two points that are in phase.
(ii) Determine the:
(I) amplitude of the wave
(II) wavelength of the wave
(iii) Given that the frequency of the waves is 50 Hz, determine the:
(I) period
(II) speed of the wave

answers

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K.C.S.E Physics Q & A - MODEL 2018PP2QN18

29/7/2020

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K.C.S.E Physics Q & A - MODEL 2018PP2QN18

(a) (i) Draw a circuit diagram showing the depletion layer of a p—n junction diode connected in the reverse bias mode.
(ii) State the reason why increasing the external voltage in (i) makes the depletion layer wider.
(iii) State the meaning of breakdown voltage of a junction diode.
(iv) State one application of diodes.
(b) Figure 7 shows the output on a screen of a CR0 when an a.c. signal is connected to the Y-plates with the time base on.

(i) Given that the time control is 5 ms per division and the y-gain is 100 V per division determine the:
(I) frequency of the ac. signal
(II) peak voltage of the input signal
(ii) State the adjustment that may be made in order to halve the frequency of the a.c. signal.

answers

(ii) The holes and the electrons in their respective regions are attracted away from the junction by the external voltage.
(iii) The voltage at which the diode begins to conduct in the reverse bias mode.
(iv) In rectification circuits for changing a.c. to d. c.
In control of voltages of Zener diode.

(iii) Double the time control to 10ms per division.
Adjust the frequency of the source to half the value

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K.C.S.E Physics Q & A - MODEL 2018PP2QN17

29/7/2020

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K.C.S.E Physics Q & A - MODEL 2018PP2QN17

(a) Water waves from a certain Source move from the shallow end to the deep end. State the change that occurs at the deep end on the following:
(i) Frequency
(ii) Wavelength
(iii) Velocity

(b) (i) A biconvex lens forms an upright image twice the size of the object. If the focal length of the lens is 20cm, determine the object distance.
(ii) State two optical instruments which produce a magnified real image using a Convex lens.
(c) State one difference between the working of the human eye and the lens of a camera.
(d) A lens of focal length 2Ocm forms a virtual image when an object is placed 60cm from the lens. State with a reason the type of lens used.

answers

(a)(i) No change in frequency
(ii) Wavelength increases
(iii) Velocity increases

(ii) a film projector
A compound microscope
(c) In a camera focusing is done by changing the distance between the lens and the film. While in the eye focusing is done by changing the curvature of the lens.
d) Diverging lens
Forms a virtual image when the object distance is greater than the focal length.

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K.C.S.E Physics Q & A - MODEL 2018PP2QN16

29/7/2020

0 Comments

K.C.S.E Physics Q & A - MODEL 2018PP2QN16

(a) State the meaning of the following terms:
(i) Photoelectric effect
(ii) Threshold frequency
(b) Figure 5 shows some light incident on the cathode of a photocell. The photocell is connected in series with a battery, a variable resistor and a microammete

(î) Explain how the microammeter reading is affected when the intensity of the incident light is increased.
(ii) State the reason why the tube is evacuated
(c) Figure 6 shows a graph of maximum kinetic energy (KE max) of photoelectrons against the frequency of the incident radiation.

From the graph, determine:
(i) Plank’s constant h,
(ii)the threshold wavelength given that the speed of light C is 3.0 x 10⁸ms^-1

answers

(a)(i) The emission of electrons from a metal surface when light/electromagnetic radiations shine on it.
(ii) The minimum frequency of radiation required to eject electrons from a metal surface.
(b)(i) Increased intensity increases the number of electrons emitted hence a higher current reading on the microammeter.
(ii) To minimize collisions between electrons and air molecules which would cause loss of energy.

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K.C.S.E Physics Q & A - MODEL 2018PP2QN15

29/7/2020

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K.C.S.E Physics Q & A - MODEL 2018PP2QN15

(a) Electrical energy is transmitted at very high voltages and low current
(i) Describe how the high voltages are attained
(ii) State two reasons why thick aluminum wires are preferred to Copper Wires for transmission Over long distances
(b) Figure 4 shows an electric cooker connected to the mains supply, X,Y and Z are the mains wires

State with a reason the name of wire Y.
(c) A student has some coloured bulbs rated 60 W, 240 V to be connected for decorations.
(i) State the number of such bulbs that can be connected normally to a 240V supply through a 5A fuse.
(ii) If the cost of electric energy is Ksh 3.00 per kWh, determine the cost of running the bulbs in (c) (i) for 5 hours daily for 20 days.

answers

(a)(i) By use of step-up transformers low input voltages are stepped up to high voltages for transmission.
(ii) They are cheaper
They are lighter, lower density / lower weight
b) Y is the earth wire, it is connected to the casing of the cooker

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K.C.S.E Physics Q & A - MODEL 2018PP1QN18

29/7/2020

0 Comments

K.C.S.E Physics Q & A - MODEL 2018PP1QN18

(a) State two quantities that must be kept constant in order to verify Boyle’s law.
(b) An air bubble at the bottom of a beaker full of water becomes larger as it rises to the surface. State the reason why;
(i) the bubble rises to the surface,
(ii) It becomes larger as it rises.
(c) State two assumptions made in explaining the gas laws using the kinetic theory of gases.
(d) Figure 11 shows an incomplete experimental set up that was prepared by a student to verify one of the gas laws.

(i) State with a reason which one of the laws may be verified using the set up.
(ii) State what the student left out in the diagram of the set up.
(c) The volume of a fixed mass of a gas reduced from 500 cm³ to 300 cm³ at constant pressure. The initial temperature was 90K. Determine the final temperature

answers

(a) Mass
Temperature
(b)(i) The gas is less dense than the water.
(ii) As it rises the pressure around the bubble reduces and since the temperature is the same, the volume increases.
(c) The size of the molecules is assumed to be negligible.
Intermolecular forces are also assumed to be negligible.
Real gases can never have zero volume yet the gas laws assume presence of zero volume.
(d)(i) The pressure law.
Has ability to measure the temperature and the pressure while keeping the volume constant.
(ii) Source of heating for the temperature to be changed.

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<<Previous

​(a) Define Radio-activity (2mks)

​(b) When carrying out experiments with radioactive substances the source should never be held with bare hands but with forceps. Explain? (1mk)

​(i) Plot on the graph paper provided the graph of the count rate (y-axis) against time

​(ii) From the graph, determine the half-life of Radon-220 (1mk)

​(e) The diagram in the figure below shows paths taken by three radiations A,B and C from a radioactive isotope through an electric field.

​(i) State the charge on plate Y (1mk)

​(ii) Identify the radiations A and C (2mks)

​(iii) Give a reason why C deviates more than A (1mk)

(a) A 240v mains transformer has 800 turns in the primary and N turns in the secondary. It is used to supply energy to a 12v/21w lamp. ​

(i) Calculate the number of turns in the secondary (2mks)

(ii) What is the efficiency of the transformer if the current drawn from the 240V mains is 100mA (2mks)

​Calculate.

(i) the reading of voltmeter, V, with, S, open (2mks)

(ii) the reading of the ammeter A with S closed (neglect the effective resistance of the secondary winding) (2mks)

(iii) the power dissipated in the lamp (2mks)

(iv) the primary current if the transformer is 90% efficient (3mks)

​(a) State two advantages of a C.R.O as a voltmeter

​(b) A television tube is a cathode ray tube modified. State two modifications

​(c) State the functions of the following parts of a C.R.O

(i) Grid

(ii) X-plates

(iii) Fluorescent screen

​(d) A modern X-ray tube is shown below

​(i) Name the parts labeled A-D (2mks)

A

B

C

D

​(ii) Give the functions of:- (1mk)

(i) Shielding with lead

(ii) Evacuating the tube

​(a) Define doping (1mk)

​(b) Distinguish between a p-type and n-type semi conductors (2mks)

​(c) Using a diagram illustrate a forward P-N junction (2mks)

​(d) The figure below shows a bridge circuit

​(i) Sketch of the figure below the wave form when a CRO is connected across the resistor, R

​(ii) On the same axes, sketch a wave form when C.R.O is connected across R when the capacitor has been removed (1mk)

​(a) Explain why bulbs in along corridor are not wired in series (2mks)

​(b) An electric cooker has an oven rated 2500w, a grill rated 1500w and two plates each of 1000W. This cooker operates directly from 240v supply. What is the costs of operating all the parts at once for 30 minutes if electricity costs sh.10.00 per unit? (3mks)

​(c) Study the figure below

​(i) What name is given to the fitting in the diagram (1mk)

​(ii) Identify the parts labeled (2mks)

A

B

C

D

​(a) The diagram in the figure below represents a wheel and axle used as a machine, whose efficiency is 80% to raise 400N of building materials. The wheel and axles have diameters of 75cm and 15cm respectively.

​(i) Mark on the diagram the correct position and direction of the load to be lifted (1mk)

​(ii) Name the principle on which this machine works (1mk)

​(iii) Calculate the effort needed to raise the load (3mks)

​(iv) The machine is operated manually and raises the load to a height of 5m in 20 seconds. Calculate the power developed by the operator (2mks)

(b) ​(i) State two factors that determines the efficiency of an inclined plane as a machine (2mks)

​(ii) Explain how these factors affect efficiency (2mks)

​Explain what you understand by each of the following terms:

(​i) Angular velocity (1mk)

​(ii) Centripetal force (1mk)

​b) A bicycle wheel with radius 28cm moves with a linear velocity of 8m/s, determine

​(i) the angular velocity of the wheel (2mks)

​(ii) the centripetal acceleration of a point on the rim of the wheel (2mks)

​(c) To determine the relationship between angular velocity w and tension T, a student used a smooth disc with a hole at the centre, a string and cylindrical object of mass m, as shown below

​Describe how the student went about determining the relationship, specifying any other necessary material or instrument not shown in the diagram (3mks)

(a) ​(i) Other than time, state the measurements that would be used to determine the quantity of heat P absorbed by ice in a unit time (2mks)

​(ii) Complete the circuit to show the connection of the essential circuit components (2mks)

​(iii) Describe how the student would proceed to determine P (3mks)

​(iv) Give a reason why P may not be equal to the value indicated by the manufacturer (1mk)

(b) In another experiment, 100g of hot water at 90oC was mixed with 20g of ice at 0oC in a lagged plastics colorimeter. After stirring, all the ice melted and the temperature of the mixture was found to be 61.5oC. Determine the latent heat of fusion of ice (3mks)

(a) ​(i) Complete the table to show the values of extension (2mks)

​(ii) Draw a graph of extension (y-axis) against load for the spring (5mks)

​(ii) Determining form the graph the proportionality constant of the spring (2mks)

​(b) Two springs Q and R have proportionality constants 20N/M and 25N/M respectively. Q weighs 0.2 N while the weight of R is negligible. The two springs are arranged to support a load of 3.0N as shown in the diagram below

Determine the extension in (i) Q……………………………………………..(1mk)

ii) R ……………………………………………(1mk)

​(c) State two factors that determine the proportionality constant of a helical spring (2mks)

​(a) State with reason the total momentum of the trolleys when they are just released (2mks)

​(b) Calculate the initial acceleration of trolley A when released (3mks)

(c) The velocity of the trolley B is 0.9ms-1 just before it collides with A. Determine the velocity of A just before the collision

​(d) Which trolley covers a longer distance before collision? Explain (2mks)

​(e) Explain why the elastic strip may not stretch to the same original length after impact (2mks)

K.C.S.E Physics Q & A - MODEL 2019PP2QN19

K.C.S.E Physics Q & A - MODEL 2019PP1QN18

(a) Define Radio-activity (2mks)

(b) When carrying out experiments with radioactive substances the source should never be held with bare hands but with forceps. Explain? (1mk)

(i) Plot on the graph paper provided the graph of the count rate (y-axis) against time

(ii) From the graph, determine the half-life of Radon-220 (1mk)

(e) The diagram in the figure below shows paths taken by three radiations A,B and C from a radioactive isotope through an electric field.

(i) State the charge on plate Y (1mk)

(ii) Identify the radiations A and C (2mks)

(iii) Give a reason why C deviates more than A (1mk)

(a) A 240v mains transformer has 800 turns in the primary and N turns in the secondary. It is used to supply energy to a 12v/21w lamp.

Calculate.

(a) State two advantages of a C.R.O as a voltmeter

(b) A television tube is a cathode ray tube modified. State two modifications

(c) State the functions of the following parts of a C.R.O

(d) A modern X-ray tube is shown below

(i) Name the parts labeled A-D (2mks)

(ii) Give the functions of:- (1mk)

(a) Define doping (1mk)

(b) Distinguish between a p-type and n-type semi conductors (2mks)

(c) Using a diagram illustrate a forward P-N junction (2mks)

(d) The figure below shows a bridge circuit

(i) Sketch of the figure below the wave form when a CRO is connected across the resistor, R

(ii) On the same axes, sketch a wave form when C.R.O is connected across R when the capacitor has been removed (1mk)

(a) Explain why bulbs in along corridor are not wired in series (2mks)

(b) An electric cooker has an oven rated 2500w, a grill rated 1500w and two plates each of 1000W. This cooker operates directly from 240v supply. What is the costs of operating all the parts at once for 30 minutes if electricity costs sh.10.00 per unit? (3mks)

(c) Study the figure below

(i) What name is given to the fitting in the diagram (1mk)

(ii) Identify the parts labeled (2mks)

(a) The diagram in the figure below represents a wheel and axle used as a machine, whose efficiency is 80% to raise 400N of building materials. The wheel and axles have diameters of 75cm and 15cm respectively.

(i) Mark on the diagram the correct position and direction of the load to be lifted (1mk)

(ii) Name the principle on which this machine works (1mk)

(iii) Calculate the effort needed to raise the load (3mks)

(iv) The machine is operated manually and raises the load to a height of 5m in 20 seconds. Calculate the power developed by the operator (2mks)

(b)
(i) State two factors that determines the efficiency of an inclined plane as a machine (2mks)

(ii) Explain how these factors affect efficiency (2mks)

Explain what you understand by each of the following terms:

(i) Angular velocity (1mk)

(ii) Centripetal force (1mk)

b) A bicycle wheel with radius 28cm moves with a linear velocity of 8m/s, determine

(i) the angular velocity of the wheel (2mks)

(ii) the centripetal acceleration of a point on the rim of the wheel (2mks)

(c) To determine the relationship between angular velocity w and tension T, a student used a smooth disc with a hole at the centre, a string and cylindrical object of mass m, as shown below

Describe how the student went about determining the relationship, specifying any other necessary material or instrument not shown in the diagram (3mks)

(a)
(i) Other than time, state the measurements that would be used to determine the quantity of heat P absorbed by ice in a unit time (2mks)

(ii) Complete the circuit to show the connection of the essential circuit components (2mks)

(iii) Describe how the student would proceed to determine P (3mks)

(iv) Give a reason why P may not be equal to the value indicated by the manufacturer (1mk)

(b) In another experiment, 100g of hot water at 90^oC was mixed with 20g of ice at 0^oC in a lagged plastics colorimeter. After stirring, all the ice melted and the temperature of the mixture was found to be 61.5^oC. Determine the latent heat of fusion of ice (3mks)

(a)
(i) Complete the table to show the values of extension (2mks)

(ii) Draw a graph of extension (y-axis) against load for the spring (5mks)

(ii) Determining form the graph the proportionality constant of the spring (2mks)

(b) Two springs Q and R have proportionality constants 20N/M and 25N/M respectively. Q weighs 0.2 N while the weight of R is negligible. The two springs are arranged to support a load of 3.0N as shown in the diagram below

Determine the extension in
(i) Q……………………………………………..(1mk)

(c) State two factors that determine the proportionality constant of a helical spring (2mks)

(a) State with reason the total momentum of the trolleys when they are just released (2mks)

(b) Calculate the initial acceleration of trolley A when released (3mks)

(c) The velocity of the trolley B is 0.9ms^-1 just before it collides with A. Determine the velocity of A just before the collision

(d) Which trolley covers a longer distance before collision? Explain (2mks)

(e) Explain why the elastic strip may not stretch to the same original length after impact (2mks)

From the graph, determine:
(i) Plank’s constant h,
(ii)the threshold wavelength given that the speed of light C is 3.0 x 10⁸ms^-1