SUKELLEMO JOINT MOCK
Kenya Certificate of Secondary Education
PHYSICS PAPER 2
2 hours
Instructions to Candidates
- Answer all the questions in the spaces provided.
- This paper consists of 2 sections: Section A and B
- All working must be clearly shown.
- Non-programmable silent electronic calculators and KNEC mathematical tables may be used.
SECTION A: (25 MARKS)
Answer ALL questions in this section in the spaces provided:
- State two conditions under which a pinhole camera may form an image on its screen which has the same size as the object. (2mks)
- The figure below shows a ray of light incident on the surface of one plane mirror.
Sketch the path of the ray on the diagram after striking mirror 2 indicating all the angles.(2 marks) - A steel is to be magnetized by electrical method as shown below. Identify the pole P and Q of the resulting magnet. (1mk)
P:
Q: - A small chain is often seen hanging at the back of a petrol carrying lorry. State and explain its significance. (2mks)
- The figure below shows two waveforms representing the same wave motion.
Determine the velocity of the wave. (3mks) - An object O is placed in front of a concave mirror and on the principal axis, as shown in the figure below. Complete the light ray diagram to locate the position of the image. (3mks)
- Arrange the following radiations in order of increasing wavelengths. (1mk) Infrared, blue light, ultraviolet, radiowaves, x-rays.
- The figure below shows a block diagram of a p-n junction diode.
On the same diagram, show how a cell may be connected so that it is reverse biased. (1mk) - A girl standing at a distance claps her hands and hears an echo from a tall building 2 seconds later. If the speed of sound in air is 340m/s, determine how far the building is. (3mks)
- What do you understand by polarization as used in a simple cell? (1mk)
- State how the defect mentioned in question 10 above is minimized in a simple cell. (1mk)
- A current-carrying conductor AB is in a magnetic field as shown in the figure below.
- Indicate the direction of force F acting on the conductor. (1mk)
- State two factors that determine the direction of the force F. (2mks)
- You are given three resistors of values 5Ω, 8Ω and 12Ω. Show in a circuit diagram how you would connect them so as to give:
- an effective resistance of 9.8Ω. (2mks)
- the least effective resistance. (2mks)
SECTION B: (55 MARKS)
Answer ALL questions in this section in the spaces provided.
-
- Define refractive index. (1mk)
- The critical angle of a certain material medium is 43.2º. Determine the refractive index of the material. (2mks)
-
- What do you understand by the term accommodation? (1mk
- The diagram below shows a certain defect of vision. Name the defect. (1mk)
- On the figure below show how the defect can be corrected. (2mks)
- An object is placed 40cm in front of a concave lens of focal length 20cm; determine the position of the image. (3mks)
-
-
- State Lenz’s a law of electromagnetic induction. (1mk)
- A bar magnet is moved into a coil of insulated copper wire connected to a centre-zero galvanometer, as shown in the figure below.
- Show on the diagram the direction of induced current in the coil. (1mk)
- State and explain clearly what is observed on the galvanometer when the S-pole of the magnet is moved into and then withdrawn from the coil. (4mks)
- A transformer has 800 turns in the primary and 40 turns in the secondary winding. The alternating e.m.f connected to the primary is 240V and the current is 0.5A.
- Determine
- the secondary e.m.f (2mks)
- the power in the secondary if the transformer is 95% efficient. (2mks)
- Explain how energy losses in a transformer are reduced by having:
- a soft-iron core. (2mks)
- a laminated core. (1mk)
- Determine
-
-
-
- Distinguish between thermionic emission and photoelectric emission. (2mks)
- State one factor which affects the rate of each of the above types of emission.
- Thermionic emission. (1mk)
- Photoelectric emission. (1mk)
- Sodium has a work function of 2.3eV. Given that: Planck’s constant h = 6.63 x10-34JS, velocity of light in vacuum, C = 3.0 x 108m/s, 1 electron-volt (1eV) = 1.6 x 10-19 C and mass of an electron, me = 9.1 x 10-31kg, calculate:
- its threshold frequency. (2mks)
- the maximum velocity of the photoelectrons produced when the sodium is illuminated by light of wavelength 5.0 x 10-7m. (4mks)
- the stopping potential V, with the light of this wavelength. (2mks)
-
-
- State two advantages of using a Cathode Ray Oscilloscope (C.R.O) as a voltmeter over the ordinary voltmeter. (2mks)
- An X-ray operates at 30000V and the current through it is 2mA. Given that the charge of an electron is 1.6 x 10-19C, h = 6.63 x 10-34JS, speed of light, C = 3.0 x 108m/s, calculate:-
- the maximum kinetic energy of the electrons when hitting the target. (2mks)
- the number of electrons hitting the target per second. (2mks)
- the minimum wavelength of the X-rays emitted. (2mks)
-
- A radioactive carbon-14 decays to nitrogen by beta particles as shown below.
146C = x7N+0ey
Determine the values of x and y. (2mks) - The graph below shows radioactive decay of iodine.
Use the graph to determine the:-- Fraction of the amount remaining after 16.2 days. (2mks)
- Determine the half – life of iodine. (2mks)
- Mass remaining after 17 days.
- The figure below shows the cross-section of a diffusion cloud chamber used to detect radiation from radioactive sources.
- State the function of the following:
- Alcohol. (1mk)
- Solid CO2. (1mk)
- Explain briefly how the diffusion cloud chamber can be used to detect and identify alpha particles. (3mks)
- State the function of the following:
- A radioactive carbon-14 decays to nitrogen by beta particles as shown below.
MARKING SCHEME
SECTION A: (25 MARKS)
Answer ALL questions in this section in the spaces provided:
- State two conditions under which a pinhole camera may form an image on its screen which has the same size as the object. (2mks)
- When the object distance from the pinhole is equal to the image distance.
- When the screen is as large as the object.
- When the object distance from the pinhole is equal to the image distance.
- The figure below shows a ray of light incident on the surface of one plane mirror.
Sketch the path of the ray on the diagram after striking mirror 2 indicating all the angles.(2 marks)-
X= 2Ө
= 2 × 15
30º
-
- A steel is to be magnetized by electrical method as shown below. Identify the pole P and Q of the resulting magnet. (1mk)
P:South Pole
Q:North Pole - A small chain is often seen hanging at the back of a petrol carrying lorry. State and explain its significance. (2mks)
- Friction generates charges on the lorry the chain discharges the lorry to prevent sparks which may lead to explosion
- Friction generates charges on the lorry the chain discharges the lorry to prevent sparks which may lead to explosion
- The figure below shows two waveforms representing the same wave motion.
Determine the velocity of the wave. (3mks)- λ= 0.4m
- T = 0.06m
V = λf
= 0.4 × 0.06
= 0.24m/s
- An object O is placed in front of a concave mirror and on the principal axis, as shown in the figure below. Complete the light ray diagram to locate the position of the image. (3mks)
Answer - Arrange the following radiations in order of increasing wavelengths. (1mk) Infrared, blue light, ultraviolet, radiowaves, x-rays.
- X-ray → Ultraviolet → Blue light → Infrared → Radio waves
- X-ray → Ultraviolet → Blue light → Infrared → Radio waves
- The figure below shows a block diagram of a p-n junction diode.
On the same diagram, show how a cell may be connected so that it is reverse biased. (1mk)
Answer - A girl standing at a distance claps her hands and hears an echo from a tall building 2 seconds later. If the speed of sound in air is 340m/s, determine how far the building is. (3mks)
- V=2s/t
S=Vt/2
=340 x 2/2
340m
- V=2s/t
- What do you understand by polarization as used in a simple cell? (1mk)
- Process by which hydrogen gas bubbles form an insulating layer on the positive copper plate
- Process by which hydrogen gas bubbles form an insulating layer on the positive copper plate
- State how the defect mentioned in question 10 above is minimized in a simple cell. (1mk)
- Adding potassium dichromate powder/depolarizing agent/oxidizing agent which oxidizes hydrogen to water
- Adding potassium dichromate powder/depolarizing agent/oxidizing agent which oxidizes hydrogen to water
- A current-carrying conductor AB is in a magnetic field as shown in the figure below.
- Indicate the direction of force F acting on the conductor. (1mk)
- State two factors that determine the direction of the force F. (2mks)
- Direction of magnetic field
- Direction of magnetic field
- Indicate the direction of force F acting on the conductor. (1mk)
- You are given three resistors of values 5Ω, 8Ω and 12Ω. Show in a circuit diagram how you would connect them so as to give:
- an effective resistance of 9.8Ω. (2mks)
- the least effective resistance. (2mks)
- an effective resistance of 9.8Ω. (2mks)
SECTION B: (55 MARKS)
Answer ALL questions in this section in the spaces provided.
-
- Define refractive index. (1mk)
- Refractive index is ratio of sine of angle of incidence to the sine of angle of refraction for a given pair of media
- Refractive index is ratio of sine of angle of incidence to the sine of angle of refraction for a given pair of media
- The critical angle of a certain material medium is 43.2º. Determine the refractive index of the material. (2mks)
- 1.4608
-
- What do you understand by the term accommodation? (1mk)
- Accommodation is the fine adjustment of focal length of the eye so as to fit images of objects of different distances on the retina
- Accommodation is the fine adjustment of focal length of the eye so as to fit images of objects of different distances on the retina
- The diagram below shows a certain defect of vision. Name the defect. (1mk)
- Long sightedness or (hypermetropia)
- Long sightedness or (hypermetropia)
- On the figure below show how the defect can be corrected. (2mks)
Answer
- What do you understand by the term accommodation? (1mk)
- An object is placed 40cm in front of a concave lens of focal length 20cm; determine the position of the image. (3mks)
- 1/-f = 1/V + 1/U
-1/20 = 1/V + 1/U
1/V = 1/20 - 1/40 = -2-1/40 = 3/40
V= -40/3 = 13.3cm
- 1/-f = 1/V + 1/U
- Define refractive index. (1mk)
-
-
- State Lenz’s a law of electromagnetic induction. (1mk)
- Lenz’s law – The direction of the induced current is such that the induced current which it causes to flow produces a magnetic effect that oppose the change producing it.
- Lenz’s law – The direction of the induced current is such that the induced current which it causes to flow produces a magnetic effect that oppose the change producing it.
- A bar magnet is moved into a coil of insulated copper wire connected to a centre-zero galvanometer, as shown in the figure below.
- Show on the diagram the direction of induced current in the coil. (1mk)
- State and explain clearly what is observed on the galvanometer when the S-pole of the magnet is moved into and then withdrawn from the coil. (4mks)
- S-Pole of magnet moved into the coil.
-Galvanometer deflects to the left (on one side) momentarily. -Induced current in the coil flows so as to form a South Pole at the end of the coil near the magnet. - S-Pole of magnet withdrawn.
-Galvanometer reverses its direction of deflection/deflects to the right momentarily.
-Changing the direction of motion reverses the direction of induced current so that the end of the coil tends to form a N-Pole so as to oppose the motion of the magnet out of the coil.
- S-Pole of magnet moved into the coil.
- Show on the diagram the direction of induced current in the coil. (1mk)
- State Lenz’s a law of electromagnetic induction. (1mk)
- A transformer has 800 turns in the primary and 40 turns in the secondary winding. The alternating e.m.f connected to the primary is 240V and the current is 0.5A.
- Determine
- the secondary e.m.f (2mks)
Vp = 240V
Ip = 0.5A
Ns/Np = Vs/Vp
40/800 = Vs/240
Vs= (40 x 240)/800
=12V - the power in the secondary if the transformer is 95% efficient. (2mks)
- VsIs = 95% VpIp
95/100 x 240 x0.5
=114W
- VsIs = 95% VpIp
- the secondary e.m.f (2mks)
- Explain how energy losses in a transformer are reduced by having:
- a soft-iron core. (2mks)
- Soft iron is easily magnetized and easily demagnetized; this reduces heat loss due magnetization and demagnetization (hysteresis loss)
- Soft iron is easily magnetized and easily demagnetized; this reduces heat loss due magnetization and demagnetization (hysteresis loss)
- a laminated core. (1mk)
- Laminated core increases resistance of the core which reduces the size of eddy currents thus reducing heating due to the eddy currents.
- a soft-iron core. (2mks)
- Determine
-
-
-
- Distinguish between thermionic emission and photoelectric emission. (2mks)
- Thermionic emission – Is the escape or evaporation of electrons from a metal surface when heated
- Photoelectric emission – Is the escape or evaporation of electrons from a metal surface when light of suitable frequency falls on the metal surface.
- State one factor which affects the rate of each of the above types of emission.
- Thermionic emission. (1mk) - Temperature of metal/ type of metal
- Photoelectric emission. (1mk) - Frequency of incident light/ Work function/ threshold frequency of the metal
- Distinguish between thermionic emission and photoelectric emission. (2mks)
- Sodium has a work function of 2.3eV. Given that: Planck’s constant h = 6.63 x 10-34JS, velocity of light in vacuum, C = 3.0 x 108m/s, 1 electron-volt (1eV) = 1.6 x 10-19 C and mass of an electron, me = 9.1 x 10-31kg, calculate:
- its threshold frequency. (2mks)
- hfo = wo
6.63 x 10-34fo=2.3 x 1.6 x10-19
fo = 5.55 x 1014HZ
- hfo = wo
- the maximum velocity of the photoelectrons produced when the sodium is illuminated by light of wavelength 5.0 x 10-7m. (4mks)
- hf = wo + 1/2MV2
hc/λ = Wo + 1/2MV2
6.63 x 10-34 x 3.0x108 = 2.3 x 1.6 x 10-19 + 1/2MV2
5.0 x 10-7
3.978 x 10-19 = 3.68 x 10-19 + 1/2MV2
1/2MV2 = 0.298 x 10-19
- hf = wo + 1/2MV2
- the stopping potential V, with the light of this wavelength. (2mks)
- eVs = 1/2MV2
1.6 x 10-19Vs = 0.298 x 10-19
Vs= 0.298 x 10-19
1.6 x 10-19
=0.186Volts
- eVs = 1/2MV2
- its threshold frequency. (2mks)
-
-
- State two advantages of using a Cathode Ray Oscilloscope (C.R.O) as a voltmeter over the ordinary voltmeter. (2mks)
- Has no coil to burn out
- Has instantaneous response.
- Has nearly infinite resistance, therefore draws very little current.
- Can measure both AC and DC voltages.
- An X-ray operates at 30000V and the current through it is 2mA. Given that the charge of an electron is 1.6 x 10-19C, h = 6.63 x 10-34JS, speed of light, C = 3.0 x 108m/s, calculate:-
- the maximum kinetic energy of the electrons when hitting the target. (2mks)
- Ke = ½MV2 = eV
= 1.6 × 10-19 × (30,000)2
= 1.44 × 10-10J
- Ke = ½MV2 = eV
- the number of electrons hitting the target per second. (2mks)
- I=ne
2 x 10-3 = n x 1.6 x 10-19
n= 2x 10-3
1.6 x 10-19
=1.25 x 1016 electrons
- I=ne
- the minimum wavelength of the X-rays emitted. (2mks)
- hfmax = eV But fmax= e/λmin
h e/λmin = eV
λmin =hc/eV
= 6.63 x 10-34 x 3 x 108
1.44 x 10-10
= 1.38 x 10-15m
- hfmax = eV But fmax= e/λmin
- the maximum kinetic energy of the electrons when hitting the target. (2mks)
- State two advantages of using a Cathode Ray Oscilloscope (C.R.O) as a voltmeter over the ordinary voltmeter. (2mks)
-
- A radioactive carbon-14 decays to nitrogen by beta particles as shown below.
146C = x7N+0ey
Determine the values of x and y. (2mks)- 14=x+0
x=14
6=7+y
y=-1
- 14=x+0
- The graph below shows radioactive decay of iodine.
Use the graph to determine the:-- Fraction of the amount remaining after 16.2 days. (2mks)
- Determine the half – life of iodine. (2mks)
- T½ = 7500 -2500 = 5000 years
- T½ = 7500 -2500 = 5000 years
- Mass remaining after 17 days.
- No of halflifes = 15000/5000
N1 =No(½)3
100(½)3
=12.5g
- No of halflifes = 15000/5000
- The figure below shows the cross-section of a diffusion cloud chamber used to detect radiation from radioactive sources.
- State the function of the following:
- Alcohol. (1mk)
- Alcohol condenses around the ions formed by the radiation to form the narrow tracks
- Alcohol condenses around the ions formed by the radiation to form the narrow tracks
- Solid CO2. (1mk)
- Cools the bottom of the chamber and also condenses alcohol below its normal temperature
- Cools the bottom of the chamber and also condenses alcohol below its normal temperature
- Alcohol. (1mk)
- Explain briefly how the diffusion cloud chamber can be used to detect and identify alpha particles. (3mks)
- Sold CO2 cools the bottom of the chamber alcohol vapourises and spreads through the chamber. It is cooled below its normal temperature in case of a radiation, air around the path of the radiation is ionized. Alcohol condenses around these ions to form a narrow cloud.
- State the function of the following:
- A radioactive carbon-14 decays to nitrogen by beta particles as shown below.
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