Free KCSE Physics Topical Questions KNEC Standards

K.C.S.E Physics Q & A - MODEL 2019PP2QN14

31/7/2020

K.C.S.E Physics Q & A - MODEL 2019PP2QN14

Figure 6 shows radiation from the sun passing through glass in a greenhouse onto the floor. The floor then emits radiation

State the name of the radiation emitted by the floor.

answer

Infrared

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

29/7/2020

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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 2017PP2QN16

28/7/2020

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K.C.S.E Physics Q & A - MODEL 2017PP2QN16

(a) Figure 7 shows a set up that may be used to observe photoelectric effect. A radiation is incident on the cathode. it is observed that the microammeter registers a current.

(i) Explain how the current is produced.
(ii) State with a reason what must be done for a higher current to be registered.
(iii) It was observed that for a certain incident radiation, no current was registered.
Explain this observation.
(b)A monochromatic light of wavelength 4.50 X 10^-7 m is incident on a metal surface of threshold frequency 5.5 X 10¹⁴ Hz. (Speed of light c is 3.0 X 10⁸ms and planks constant h is 6.63 X 10^-34Js).
Determine
(i) the work function of the metal surface,
(ii) average kinetic energy of the emittal photoelectrons.

answers

a)i. Radiations cause photo electrons to be ejected from the metal surface (cathode), the electrons are attracted by the anode hence current flows.
ii)Source is made moved closer! increase anode voltage/accelerating voltage.
iii. The frequency of the incident radiation is below the thrsio1d frequency of the surface hence no emission can take place.

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K.C.S.E Physics Q & A - MODEL 2015PP2QN14

24/7/2020

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K.C.S.E Physics Q & A - MODEL 2015PP2QN14

(a) State two factors that affect photoelectric emission.
(b) Light of wavelength 4.3 x 10^-7m is incident on two different metal surfaces, nickel and potassium. (Take speed of light as 3.0 x 10⁸ ms^-1 and planks constant h as 6.63 x 10^-34Js).

(i) Determine the energy of the incident radiation.
(ii) If the work function of nickel is 8.0 x 10^-19J and that of potassium is 3.68 x 10^-19J, state with a reason from which of the two metals the given light will eject electrons.
(iii) Determine the velocity of the emitted electrons from the metal surface in b(ii).
(Take the mass of an electron as 9.1 x 10^-31 kg).

answers

(a) Energy of incident radiation
Work function of the metal
Intensity of the radiation

(ii) Potassium
The work function of potassium is less than the energy of the incident radiation

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State one application of thermionic emission.

24/7/2020

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K.C.S.E Physics Q & A - MODEL 2015PP2QN11

State one application of thermionic emission.

answer

.Production of cathode rays / x-rays.

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K.C.S.E Physics Q & A - MODEL 2013PP2QN12

23/7/2020

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K.C.S.E Physics Q & A - MODEL 2013PP2QN12

A photon of ultraviolet light having energy E falls on a photoemissive surface whose work function is T. Write an expression for the maximum kinetic energy of the resulting photoelectron in terms of E and T.

answer

K= E-T

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State the meaning of the term “threshold frequency” as used in photoelectric emission.

20/7/2020

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K.C.S.E Physics Q & A - MODEL 2011PP2QN14

State the meaning of the term “threshold frequency” as used in photoelectric emission.

answer

The minimum frequency of an incident radiation to cause emission of photo electrons.

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K.C.S.E Physics Q & A - MODEL 2010PP2QN19

19/7/2020

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K.C.S.E Physics Q & A - MODEL 2010PP2QN19

(a) State the property of radiation that determines the number of electrons emitted when a radiation falls on a metal surface.
(b) Figure 15 is a graph of the stopping potential Vs against frequency in an experiment on photoelectric effect.

(i) What is meant by stopping potential?
(ii) Given that the stopping potential Vs is related to the frequency by the equation

answers

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K.C.S.E Physics Q & A - MODEL 2010PP2QN13

19/7/2020

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K.C.S.E Physics Q & A - MODEL 2010PP2QN13

The wavelength of a radio wave is 1km. Determine its frequency.
(Take the speed of light as 3.0 x 108 ms^-1)

answer

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K.C.S.E Physics Q & A - MODEL 2009PP2QN18

17/7/2020

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K.C.S.E Physics Q & A - MODEL 2009PP2QN18

(a) It is observed that when ultra- violet radiation is directed onto a clean zinc plate connected to the cap of a negatively charged leaf electroscope, the leaf falls
(i) Explain this observation
(ii) State why this observation does not occur if the electroscope is positively Charged
(iii) Explain why the leaf of the electroscope does not fall when infra- red radiation is directed onto the zinc plate

(b) State the effect on the electrons emitted by the photoelectric effect when:
(i) The intensity of incident radiation is increased
(ii) The frequency of the incident radiation is increased
(c) The maximum wavelength required to cause photoelectric emission on a metal surfaces is 8.0 x 10^-7m. The metal surface is irradiated with light of frequency 8.5 x 10¹⁴ Hz.
Determine:
(i) The threshold frequency
(ii) The work function of the metal in electron volts
(iii) The maximum kinetic energy of the electrons
Take: leV= 1.6 x 10^-19J.
Speed of light = 3.0 x 108 ms^-1
Plank's constant, h = 6.63 x 10^-34 Js

answers

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K.C.S.E Physics Q & A - MODEL 2007PP2QN11&12

15/7/2020

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K.C.S.E Physics Q & A - MODEL 2007PP2QN11&12

The graph in figure 8 shows the variation of photoelectric current with applied voltage when a surface was illuminated with light of a certain frequency. Use the information in the figure to answer questions 11 and 12

On the same axes, sketch the graph when light of higher intensity but same frequency is used to illuminate the surface.
Explain your answer in 11 above

ANSWERS

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K.C.S.E Physics Q & A - MODEL 2006PP2QN12&13

14/7/2020

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K.C.S.E Physics Q & A - MODEL 2006PP2QN12&13

Figure 6 shows a tube for investing the properties of a beam of electrons. Use the information in the figure to answer questions 12 and 13

12. What property of the beam of electrons show that the electrons are traveling at a very high speed?
13. The beam of electrons is subjected to a strong magnetic field which is perpendicular to the path and into the paper. Sketch on the same figure, the new path of electrons.

ANSWER

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K.C.S.E Physics Q & A - MODEL 2006PP2QN10&11

14/7/2020

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K.C.S.E Physics Q & A - MODEL 2006PP2QN10&11

What is meant by the term work function?
If the frequency of the illuminating radiation is just equal to the threshold frequency of the surface explain why no photoelectric effect is observed

ANSWERS

Work function of a metal is the minimum energy required to set free (release) an electron from the surface of the metal
Threshold frequency K.E of electron = 0 hence velocity of the electron would be zero; (No motion) thus photo electric effect cannot be observed

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K.C.S.E Physics Q & A - MODEL 2004PP2QN07

12/7/2020

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K.C.S.E Physics Q & A - MODEL 2004PP2QN07

a) i) What is photoelectric effect?
ii) You are provided with the following:
a photocell, a source uv light, a rheostat, a source of e.m.f, a milliammeter, a voltmeter and connecting wires. Draw a circuit diagram to show how photoelectric effect may be demonstrated in the laboratory.
b) In a photoelectric effect experiment, a certain surface was illuminated with radiation of different frequencies and the stopping potential determined for each frequency
Table 2 shows the results obtained.

(i) Plot the graph of the graph of stopping potential (y-axis) against frequency.
(ii) Determine Planks Constant, h, and the work function,of the surface given that eVs = hf- hfo where e= 1.6x 10^-19 coulomb and hf = 0(thita)fo is the lowest frequency that can cause photoelectric effect.
c) A surface whose work function = 6.4 x 10^-19 joules is illuminated with light of frequency 3.0 x 10 ¹⁵HZ
Find the maximum Kinetic energy of the emitted photoelectrons (Use the Value of H obtained in b(ii)

answers

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K.C.S.E Physics Q & A - MODEL 2003PP1QN35

12/7/2020

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K.C.S.E Physics Q & A - MODEL 2003PP1QN35

The minimum frequency of radiation necessary to cause photoelectric effect on a certain metal surface in 9.06 x 10¹⁴ Hz. Determine the work function fo the metal.(planks constant h = 6.63 x 10^-34

ANSWER

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Light of a certain wavelength strikes the surface of a metal. State what determines the maximum kinetic energy of the electron emitted.

10/7/2020

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K.C.S.E Physics Q & A - MODEL 2002PP1QN34

Light of a certain wavelength strikes the surface of a metal. State what determines the maximum kinetic energy of the electron emitted.

answer

Work function of metal / min energy required to eject e-1 for excess energy work function.

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K.C.S.E Physics Q & A - MODEL 1999PP2QN07

7/7/2020

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K.C.S.E Physics Q & A - MODEL 1999PP2QN07

a) Figure 7 shows a photoelectric cell cirucuit:

The intensity of the light can be varied.
i) Describe how the circuit may be used to show how the current I varies with the potential difference V across the cell.
ii) Sketch on the same axis graphs of I versus V for three different values of light intensity E1E2 and E3 such that E3>E2>E1
b) Using a circuit similar to the one in figure 7. with the polarity of the batteries reversed, the frequency, of the light was varied at constant intensity. For each frequency, the potential difference was varied until the current was equal to zero. The value of this voltage, Vco was noted. The graph in figure 8 shows the relation between Vco and the frequency , of the incident light.Feom the graph, determine the:
i) Value of planks constant, h (charge an electron e = 1.6 x 10-19Colubomb)
ii) Work function, of the cathode surface of the cell . (Give your answers to 2 decimal places.)

answers

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K.C.S.E Physics Q & A - MODEL 1996PP2QN07

5/7/2020

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K.C.S.E Physics Q & A - MODEL 1996PP2QN07

(a) Describe with the aid of a diagram an experiment set up for observing photoelectric effect
(b) Table 2 shows the relationship between the wavelength, of a radiation falling on the surface and the energy, k of the emitted electrons

(i) Plot a graph of energy k ( y – axis) against the frequency, f, of the incident light
(ii) Determine the work function Φ of the surface used

(Speed of light, c = 3.00 * 108 ms^-1 planks constant h = 6.663 * 10^-34JS)

answers

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FORM I - PHYSICS SYLLABUS

Introduction to Physics (4 Lessons)
Measurements 1 (12 Lessons)
Force (16 Lessons)
Pressure (24 Lessons)
Particulate Nature of Matter (12 Lessons)
Thermal Expansion (12 Lessons)
Heat Transfer
Rectilinear Propagation of Light and Reflection at Plane Surface (16 Lessons)
Electrostatics (12 Lessons)
Cells and Simple Circuits (12 Lessons)

FORM II - PHYSICS SYLLABUS

Magnetism (12 Lessons)
Measurements II (16 Lessons)
Turning Effect of Force (10 Lessons)
Equilibrium Centre of Gravity (12 Lessons)
Reflection at Curved Surfaces (16 Lessons)
Magnetic Effect of Electric Current (18 Lessons)
Hooke's Law (8 Lessons)
Waves (14 Lessons)
Sound (12 Lessons)
Fluid Flow (14 Lessons)

FORM III - PHYSICS SYLLABUS

Linear Motion (20 Lessons)
Refraction of Light (20 Lessons)
Laws of Motion (15 Lessons)
Energy, Power and Machines (20 Lessons)
Current Electricity (20 Lessons)
Waves II(10 Lessons)
Electrostatics II (15 Lessons)
Heating Effect of Electric Current (10 Lessons)
Quantity of Heat (20 Lessons)
Gas Laws (15 Lessons)

FORM IV - PHYSICS SYLLABUS

Thin Lenses (20 Lessons)
Uniform Circular Motion (10 Lessons)
Floating and Sinking (15 Lessons)
Electromagnetic Spectrum (15 Lessons)
Electromagnetic Induction (20 Lessons)
Mains Electricity (10 Lessons)
Cathode Rays and Cathode Ray Tube (10 Lessons)
X-rays (8 Lessons)
Photoelectric Effect (15 Lessons)
Radioactivity (15 Lessons)
Electronics (10 Lessons)

K.C.S.E Physics Q & A - MODEL 2019PP2QN14

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

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

K.C.S.E Physics Q & A - MODEL 2017PP2QN16

K.C.S.E Physics Q & A - MODEL 2015PP2QN14

(a) State two factors that affect photoelectric emission. (b) Light of wavelength 4.3 x 10-7m is incident on two different metal surfaces, nickel and potassium. (Take speed of light as 3.0 x 108 ms-1 and planks constant h as 6.63 x 10-34Js).

State one application of thermionic emission.

K.C.S.E Physics Q & A - MODEL 2013PP2QN12

State the meaning of the term “threshold frequency” as used in photoelectric emission.

K.C.S.E Physics Q & A - MODEL 2010PP2QN19

K.C.S.E Physics Q & A - MODEL 2010PP2QN13

The wavelength of a radio wave is 1km. Determine its frequency. (Take the speed of light as 3.0 x 108 ms-1)

K.C.S.E Physics Q & A - MODEL 2009PP2QN18

K.C.S.E Physics Q & A - MODEL 2007PP2QN11&12

K.C.S.E Physics Q & A - MODEL 2006PP2QN12&13

K.C.S.E Physics Q & A - MODEL 2006PP2QN10&11

K.C.S.E Physics Q & A - MODEL 2004PP2QN07

K.C.S.E Physics Q & A - MODEL 2003PP1QN35

The minimum frequency of radiation necessary to cause photoelectric effect on a certain metal surface in 9.06 x 1014 Hz. Determine the work function fo the metal.(planks constant h = 6.63 x 10-34

Light of a certain wavelength strikes the surface of a metal. State what determines the maximum kinetic energy of the electron emitted.

K.C.S.E Physics Q & A - MODEL 1999PP2QN07

K.C.S.E Physics Q & A - MODEL 1996PP2QN07

(Speed of light, c = 3.00 * 108 ms-1 planks constant h = 6.663 * 10-34JS)

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FORM I - PHYSICS SYLLABUS

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FORM III - PHYSICS SYLLABUS

FORM IV - PHYSICS SYLLABUS

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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

(a) State two factors that affect photoelectric emission.
(b) Light of wavelength 4.3 x 10^-7m is incident on two different metal surfaces, nickel and potassium. (Take speed of light as 3.0 x 10⁸ ms^-1 and planks constant h as 6.63 x 10^-34Js).

The wavelength of a radio wave is 1km. Determine its frequency.
(Take the speed of light as 3.0 x 108 ms^-1)

The minimum frequency of radiation necessary to cause photoelectric effect on a certain metal surface in 9.06 x 10¹⁴ Hz. Determine the work function fo the metal.(planks constant h = 6.63 x 10^-34

(Speed of light, c = 3.00 * 108 ms^-1 planks constant h = 6.663 * 10^-34JS)