(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)
(ii) Identify the radiations A and C (2mks)
(iii) Give a reason why C deviates more than A (1mk)
C more massive than A
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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(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
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)
(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)
The following is a part of a radio-active series
Identify the radiation r, find the values of c and d (3mks)r
r is βeta particle
c
c is 206
d
d is 82
Other than penetrating powers, state two differences between soft and hard X-rays (2mks)
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
A u-tube vertically holds two liquids L1 and L2 as shown in the figure above
(a) Mark accurately the point in liquid L2 that is at the same pressure as point P (1mk)
AT the same level as O in the right limb
(b) Determine the number of times L1 is denser than L2 (2mks)
The bob in the figure above is deflected then released to oscillate. State and explain one factor that will determine whether the string breaks or not (2mks)
An object weighs 2.6 N in air and 2.2N when completely immersed in water. Determine the relative density of the object (2mks)Solution
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.
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