Free KCSE Physics Topical Questions KNEC Standards

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

31/7/2020

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 2019PP2QN12

31/7/2020

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K.C.S.E Physics Q & A - MODEL 2019PP2QN12

Uranium decays as shown below.

Name the particle X that is emitted during this decay.

answer

Apha particle

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K.C.S.E Physics Q & A - MODEL 2019PP2QN11

31/7/2020

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K.C.S.E Physics Q & A - MODEL 2019PP2QN11

Figure 5 shows part of the lighting circuit in a house.

State two errors in the wiring circuit.

answers

Fuse in the neutral wire instead of the live wire
Switch to lamp A on the neutral wire instead of live wire.
Connection of lamp B on Live wires only

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K.C.S.E Physics Q & A - MODEL 2019PP2QN09

31/7/2020

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K.C.S.E Physics Q & A - MODEL 2019PP2QN09

Figure 4 shows the input and output signals on a CRO screen when two diodes are used during a full wave rectification.

Explain how the two diodes rectify the input signal.

answers

During the first half cycle of the input signal, current flows in the first diode
During the second half cycle of the input signal, current flows in the second diode
When the current through the two diodes are combined a fully rectified wave signal is obtained as the output signal.

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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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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 2019PP2QN19

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

K.C.S.E Physics Q & A - MODEL 2019PP2QN12

K.C.S.E Physics Q & A - MODEL 2019PP2QN12

K.C.S.E Physics Q & A - MODEL 2019PP2QN11

K.C.S.E Physics Q & A - MODEL 2019PP2QN11

K.C.S.E Physics Q & A - MODEL 2019PP2QN09

K.C.S.E Physics Q & A - MODEL 2019PP2QN09

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

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

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FORM I - PHYSICS SYLLABUS

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FORM III - PHYSICS SYLLABUS

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