Free KCSE Physics Topical Questions KNEC Standards

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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Other than penetrating powers, state two differences between soft and hard X-rays

20/10/2021

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Other than penetrating powers, state two differences between soft and hard X-rays (2mks)

Hard X-ray have short wavelength and are produced at high voltages (1mk)
Soft X-rays have longer wavelength and are produced at lower voltages (1mk)

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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 2017PP2QN19

28/7/2020

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K.C.S.E Physics Q & A - MODEL 2017PP2QN19

(a) Figure 10 shows a block diagram of a cathode ray oscilloscope (CRO).

State the names of the parts labelled B₁ and B₂.
(ii) State and explain the function of the part marked A.
(b) Figure 11 shows a trace of a signal observed on the screen of a CRO. The time-base setting is 20 mscm^-2

Determine the frequency of the signal.
(c) Explain why tunsten is used as a target in an x-ray tube.

answers

a) (i) B1 — y deflecting plates
B2 — x deflecting plates
(ii) Grid; controls the intensity by controlling the number of electrons reaching the screen.
If made more negative less electrons pass through.

c) Tungsten has a high melting point.
It can with stand high temperatures.

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K.C.S.E Physics Q & A - MODEL 2015PP2QN12

24/7/2020

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K.C.S.E Physics Q & A - MODEL 2015PP2QN12

Figure 4 shows a cathode ray entering into a region between two charged plates.

Complete the diagram to show the path of the ray in the field.

answer

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K.C.S.E Physics Q & A - MODEL 2014PP2QN13

23/7/2020

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K.C.S.E Physics Q & A - MODEL 2014PP2QN13

The current of electrons hitting the screen of a cathode ray oscilloscope is 2.0 X 10^-4A
Determine the number of electrons that strike the screen each second. (take charge of an electron as 1.6 X 10 ^-19C).

answer

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K.C.S.E Physics Q & A - MODEL 2013PP2QN017

23/7/2020

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K.C.S.E Physics Q & A - MODEL 2013PP2QN017

(a) Figure 9 shows a cathode ray tube in which a beam of electrons is cast on the screen.

(i) state how the electrons are produced in the tube.
(ii) state how the electron beam is detected.
(iii) State the reason for having a variable potential difference (p.d.) at the:
(I) grid;
(II) anodes.
(b) Figure 10 shows the waveform of a signal applied at the y-plates of an oscilloscope whose time-base is switched to the scale of 2 milliseconds per centimeter.

Determine:
(i) the period of the signal;
(ii) the frequency of the signal.

ANSWERS

(a) (I) Thermionically by cathode
(ii) causing fluorescence on screen
(iii) (i) control brightness of fluorescence
(ii) to focus the electron beam

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K.C.S.E Physics Q & A - MODEL 2012PP2QN013

21/7/2020

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K.C.S.E Physics Q & A - MODEL 2012PP2QN013

Figure 11, shows an alternating current (a.c) connected across a diode D and a resistor R.

On the axes provided sketch the output as observed in the CRO connected across R.

answer

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K.C.S.E Physics Q & A - MODEL 2011PP2QN18

20/7/2020

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K.C.S.E Physics Q & A - MODEL 2011PP2QN18

(a) State two differences between cathode rays and electromagnetic radiations.
(b) Figure 10, shows the main features of a cathode ray oscilloscope (CRO)

(i) Name the parts labelled M and N.
M
N
(ii) Explain how electrons are produced in the tube.
(iii) When using the CRO to display waveforms of voltages, state where the following should be connected:
(I) the voltage to be displayed on the screen;
(II) the time base voltage.
(iv) state why the tube is highly evacuated.
(c) Figure 11, shows the waveform of a voltage displayed on the screen of a CRO.
The Y-gain calibration was 5V per cm.

(i) Determine the peak-to-peak voltage of the Y-input.
(ii) Sketch on the same figure the appearance of the waveform after the voltage of the input signal is halved and it’s frequency is doubled.

answers

(a) -Cathode rays have charge but e.m radiations don’t have charge;
-Cathode rays are particles and have a mass but e.m radiations are waves;
-Cathode rays travel at a speed depending on the accelerating voltage but e.m radiations
travel at the speed of light in vacuum;
- Different in the mode of production.
(b) (i) M - grid;
N - accelerating anode/anode/vacuum;
(ii) Cathode is heated by filament;
electrons are released from cathode;
by thermionic emission
(iii) (I) across Y-Y plates.
(Il) across X-X plates. (2 m
(iv) to reduce collisions, (hence ionization) with air molecules in the tube.
(c) (i) peak-to-peak voltage = 5 x 2 =10v

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K.C.S.E Physics Q & A - MODEL 2010PP2QN18

19/7/2020

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K.C.S.E Physics Q & A - MODEL 2010PP2QN18

Figure 14a, is a diagram of a cathode ray tube. M and N are parallel vertical plates.

(a) When switch S is open, a spot is seen at the centre of the screen as shown in figure 14(b).
(i) State what happens to the spot when S is closed.
(ii) State what would happen to the spot if the potential difference across MN is increased.
(iii) State what would be seen on the screen if the battery is replaced with an alternating emf of:
(I) a low frequency of about 1 Hz;
(II) a high frequency of about 50Hz.
(b) Explain the process by which electrons are produced at F.
(c) State with a reason how the brightness of the spot can be increased.
(d) The accelerating voltage of the tube is 1000V and the electron current in the beam is 1 .5mA. Determine the energy conveyed to the screen per second.

answers

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K.C.S.E Physics Q & A - MODEL 2008PP2QN12

16/7/2020

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K.C.S.E Physics Q & A - MODEL 2008PP2QN12

A narrow beam of electrons in a cathode ray oscilloscope (CRO) strike the screen producing a spot. State what is observed on the screen if a low frequency a.c source is connected across the y-input of the CRO

ANSWER

Spot moves up and down

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K.C.S.E Physics Q & A - MODEL 2007PP2QN18

15/7/2020

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K.C.S.E Physics Q & A - MODEL 2007PP2QN18

(a) Figure 14 shows the features of a cathode ray tube

(i) Name the parts labeled A and B
A …………………………………. B…………………………….
(ii) Explain how the electrons are produced in the tube
(iii) State two functions of the anodes
(iv) At what part of the cathode ray tube would the time be connected?
(v) Why is a vacuum created in the tube?
(b) The graph in figure 15 was obtained on a cathode ray oscilloscope (CRO) screen when the output of an a.c generator was connected to the input of the CRO. The time- base calibration of the CRO was set at 20 milliseconds per centimeter and the y- gain at 5 volts centimeter.

(i) Determine the pick voltage of the generator
(ii) Determine the frequency of the voltage
On the same grid, redraw the graph for the same voltage when the time base calibration is set at 40 milliseconds per centimeter and y- gain at 10 volts per centimeter. (Show at least one complete cycle)

answers

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K.C.S.E Physics Q & A - MODEL 2004PP1QN32

12/7/2020

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K.C.S.E Physics Q & A - MODEL 2004PP1QN32

Figure 17 shows the appearance of an alternating signal on a screen of a cathode ray oscilloscope.

On the same diagram, sketch the appearance of the signal when the frequency is doubled and the voltage halved.

answer

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K.C.S.E Physics Q & A - MODEL 2003PP1QN34

12/7/2020

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K.C.S.E Physics Q & A - MODEL 2003PP1QN34

Figure 18 shows the pattern produced by an A.C voltage on a CRO screen.

On the same figure, sketch the pattern produced by the same voltage when the time base is switched off.

ANSWER

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K.C.S.E Physics Q & A - MODEL 2002PP1QN29

10/7/2020

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K.C.S.E Physics Q & A - MODEL 2002PP1QN29

The circuit figure 14 represents a simple radio receiver.

On the axes provided, sketch the waveform observed on the CRO for the signal shown.

answer

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K.C.S.E Physics Q & A - MODEL 2001PP2QN04

9/7/2020

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K.C.S.E Physics Q & A - MODEL 2001PP2QN04

Fig 3 shows the main features of a cathode ray tube (CRT) of a cathode ray oscilloscope (CRO)

i) Describe how the electrons are produced in the tube.
ii) State and explain the function of the grid.
iii) State what would be observed on the screen if an a.c voltage is connected across the y-plates.
iv) State how the deflection system of a television differs fro that of a CRO.
v) Give the reason why it is possible to have a wider screen in the television set than on the C.R.O.
b) In an excited hydrogen atom. An electron moves from an energy level of -1.36 x 10 ^-19J. Determine the wavelength of the radiation emitted. (Planks constant h= 6.63 x 10^-34 Js and speed of light c= 3.0 x 108 ms^-1).

answers

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K.C.S.E Physics Q & A - MODEL 2001PP1QN31

9/7/2020

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K.C.S.E Physics Q & A - MODEL 2001PP1QN31

Fig. 22 shows an electric generator. The points P and Q are connected to a cathode ray oscilloscope (CRO)

Sketch on the axes provided the graph of the voltage output as seen on the CRO Given that when t = 0 the coil is at the position shown in the figure.

answer

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State two differences between the cathode ray tube (CRT) of a TV and the cathode ray oscilloscope (CRO)

6/7/2020

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K.C.S.E Physics Q & A - MODEL 1998PP1QN19

State two differences between the cathode ray tube (CRT) of a TV and the cathode ray oscilloscope (CRO)

answers

In TV (CRT) deflection is by magnetic field, while in CRO deflection is by electric field. X-Y plates.
ATV (CRT)has two time bases while a CRO has only one.
In CRT it produced 625 lines per second while CRO is 25 lines per second.

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The control grids in a cathode Ray Oscilloscope ( CRO) is used to control the brightness of the beam on the screen. How is this achieved?

5/7/2020

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K.C.S.E Physics Q & A - MODEL 1996PP1QN32

The control grids in a cathode Ray Oscilloscope ( CRO) is used to control the brightness of the beam on the screen. How is this achieved?

ANSWERS

Low negative voltage is applied on control grid, which control the number of electrons reaching the screen

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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)

​(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

​Other than penetrating powers, state two differences between soft and hard X-rays (2mks)

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

K.C.S.E Physics Q & A - MODEL 2017PP2QN19

State the names of the parts labelled B1 and B2. (ii) State and explain the function of the part marked A. (b) Figure 11 shows a trace of a signal observed on the screen of a CRO. The time-base setting is 20 mscm-2

K.C.S.E Physics Q & A - MODEL 2015PP2QN12

K.C.S.E Physics Q & A - MODEL 2014PP2QN13

The current of electrons hitting the screen of a cathode ray oscilloscope is 2.0 X 10-4A Determine the number of electrons that strike the screen each second. (take charge of an electron as 1.6 X 10 -19C).

K.C.S.E Physics Q & A - MODEL 2013PP2QN017

K.C.S.E Physics Q & A - MODEL 2012PP2QN013

K.C.S.E Physics Q & A - MODEL 2011PP2QN18

K.C.S.E Physics Q & A - MODEL 2010PP2QN18

K.C.S.E Physics Q & A - MODEL 2008PP2QN12

K.C.S.E Physics Q & A - MODEL 2007PP2QN18

K.C.S.E Physics Q & A - MODEL 2004PP1QN32

K.C.S.E Physics Q & A - MODEL 2003PP1QN34

K.C.S.E Physics Q & A - MODEL 2002PP1QN29

K.C.S.E Physics Q & A - MODEL 2001PP2QN04

K.C.S.E Physics Q & A - MODEL 2001PP1QN31

State two differences between the cathode ray tube (CRT) of a TV and the cathode ray oscilloscope (CRO)

The control grids in a cathode Ray Oscilloscope ( CRO) is used to control the brightness of the beam on the screen. How is this achieved?

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FORM I - PHYSICS SYLLABUS

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FORM III - PHYSICS SYLLABUS

FORM IV - PHYSICS SYLLABUS

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(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)

Other than penetrating powers, state two differences between soft and hard X-rays (2mks)

State the names of the parts labelled B₁ and B₂.
(ii) State and explain the function of the part marked A.
(b) Figure 11 shows a trace of a signal observed on the screen of a CRO. The time-base setting is 20 mscm^-2

The current of electrons hitting the screen of a cathode ray oscilloscope is 2.0 X 10^-4A
Determine the number of electrons that strike the screen each second. (take charge of an electron as 1.6 X 10 ^-19C).